3DM-GX4-45 - Hoskin Scientifique

3DM-GX4-45 - Hoskin Scientifique
LORD USER MANUAL
3DM-GX4-45™
Miniature GPS-Aided Inertial Navigation System (GPS/INS)
© 2014 LORD Corporation
MicroStrain® Sensing Systems
459 Hurricane Lane
Suite 102
Williston, VT 05495
United States of America
Phone: 802-862-6629
Toll Free: 800-449-3878
Fax: 802-863-4093
http://www.microstrain.com
[email protected]
[email protected]
Copyright © 2014 LORD Corporation
IEPE-Link™, Torque-Link™, 3DM-RQ1™, Strain Wizard® , DEMOD-DC® , DVRT ® , DVRT-Link™, WSDA® , HSLink® , TC-Link® , G-Link® , V-Link® , SG-Link® , ENV-Link™, Watt-Link™, Shock-Link™, LXRS® , Node
Commander ® , SensorCloud™, Live Connect™, MathEngine® , EH-Link® , 3DM® , FAS-A® , 3DM-GX1® , 3DMGX3® , 3DM-GX4™, 3DM-DH® , 3DM-DH3™, EmbedSense® , MicroStrain® , and Little Sensors, Big Ideas.® are
trademarks of LORD Corporation.
Document 8500-0041 Revision A
Subject to change without notice.
3DM-GX4™-45™ Inertial Navigation System User Manual
Table of Contents
1.
System Overview
6
2.
Sensor Overview
7
3.
2.1 Components
8
2.2 Interface and Indicators
9
Basic Setup and Operations
3.1 Software Installation
11
3.2 System Connections
12
3.3 Software Interface
13
3.3.1 Interactive Help Menu
13
3.4 Sensor Communication
14
3.5 GPS Link
15
3.6 Sensor Settings
15
3.6.1 Saving Configurations
4.
10
17
3.7 Data Monitoring and Recording
18
3.8 Viewing Data
21
Sensor Measurements
22
4.1 Direct Sensor Measurements (IMU Outputs)
23
4.2 Global Positioning System (GPS) Outputs
25
4.3 Computed Outputs (Estimation Filter/PVA)
27
4.4 Sensor Reference Frames
30
4.4.1 Geodetic Frame
30
4.4.2 North East Down (NED) Frame
31
4.4.3 Sensor Frame
32
4.4.4 Platform Frame
33
3DM-GX4™-45™ Inertial Navigation System User Manual
5.
6.
7.
Performance Optimization
35
5.1 Magnetometer Calibration
35
5.2 Gyroscope Bias
38
5.3 Heading Drift and Compensation
39
5.4 Angular Rate and Acceleration Limits
40
5.5 Bandwidth
40
5.6 Platform Frame Transformation
40
5.7 GPS Parameters
40
5.8 GPS Antenna Offset
41
5.9 Vehicle Dynamics Mode
42
5.10 Estimation Filter Operation
43
5.11 Estimation Filter Convergence
45
5.11.1 Initial Convergence
45
5.11.2 Bias Convergence
45
5.11.3 Output Uncertainty
45
5.12 Vibration Isolation
46
5.13 IMU Sensor Calibration
46
5.14 Temperature Compensation
46
Sensor Installation
47
6.1 Sensor Mounting
47
6.2 GPS Antenna Installation
48
OEM System Integration
49
7.1 Data Communications Protocol (DCP)
49
7.1.1 Packet Builder
50
7.1.2 Sensor Direct Mode
51
7.1.3 GPS Direct Mode
52
3DM-GX4™-45™ Inertial Navigation System User Manual
7.2 Sensor Wiring
53
7.3 Alternate GPS Equipment
54
7.3.1 GPS External Receiver
54
7.4 Sampling on Start-up
56
7.5 Connecting to a Datalogger
56
7.6 Using Wireless Adapters
56
8.
Troubleshooting
57
8.1 Troubleshooting Guide
57
8.2 Repair and Calibration
62
8.3 Technical Support
63
9.
Maintenance
10.
64
Parts and Configurations
65
10.1 Standard Configurations
65
10.2 Accessories
67
10.3 Warranty Information
68
10.4 Sales Support
69
11.
Safety Information
70
12.
References
71
12.1 Reference Documents
71
12.2 Glossary
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3DM-GX4™-45™ Inertial Navigation System User Manual
1.
System Overview
System Overview
The LORD MicroStrain ® 3DM-GX4 ™ family of industrial grade inertial sensors provides a wide
range of orientation measurements including; acceleration, angular rate, magnetic field, and
atmospheric pressure (IMU) as well as computed solutions for attitude and heading (AHRS) and
position and velocity (GPS-INS) systems. All devices include a sophisticated Extended Kalman
Filter (EKF) providing high accuracy attitude, heading, position, and velocity outputs. The IMU and
AHRS Kalman filter provide Adaptive EKF technologies to compensate for magnetic and linear
acceleration anomalies. The Kalman Filter provides sensor bias tracking, auto- zero update
options (ZUPT), and use adjustable sensor noise factors. All sensors are fully temperature
compensated and calibrated over the full operating temperature range
The use of Micro-Electro-Mechanical System (MEMS) technology allows for small, lightweight
devices. Sensors are integrated into customer systems using serial communication protocols such
as RS232 and USB. Each device comes with the LORD MicroStrain® MIP Monitor software that
can be used for device configuration, real time measurement monitoring, and data recording. The
LORD MicroStrain® MIP Data Communications Protocol that is used to communicate with LORD
MicroStrain® inertial sensors is also available for users who want to develop customized software
solutions. Because of the unified set of commands across the sensor families, it is easy to migrate
code from one inertial sensor to another.
Common applications of LORD MicroStrain ® inertial sensor products include vehicle health
monitoring, platform stabilization, down- hole and drilling operations, and inertial navigation
systems such as unmanned air and ground vehicles and personal navigation systems.
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3DM-GX4™-45™ Inertial Navigation System User Manual
2.
Sensor Overview
Sensor Overview
The 3DM- GX4- 45 ™ is a high- performance, miniature Inertial Navigation System (INS) that
combines micro inertial sensors and a high- sensitivity embedded Global Positioning System
(GPS) receiver for use in a wide range of industrial grade applications such as unmanned vehicle
navigation, robotic control, platform stabilization, motion tracking and analysis, vehicle health
monitoring, and device aiming.
The 3DM-GX4-45 ™ utilizes the strengths of integrated multi-axis gyroscopes, accelerometers,
and magnetometers in combination with GPS, temperature, and pressure readings to provide high
accuracy attitude, heading, and inertial measurements. Each of the integrated sensors is
especially good at certain tasks, and it is the weighted combination of their outputs that provides
the best estimations for AHRS and PVA systems . All measurements are temperature
compensated and are mathematically aligned to an orthogonal coordinate system. The
combination of sensors, environmental compensation and dual on- board processing with an
Extended Kalman Filter (EKF) allow the 3DM -GX4 -45 ™ to perform well in a wide variety of
applications that require ultra low noise, drift, gain, and offset errors. Settings for sensor filtering,
sensor noise, sensor bias, bias estimation, scale factor estimation, and more offer many
adjustments for specific application needs.
The 3DM-GX4-45™ communicates through a serial communications cable and is monitored by a
host computer. A detachable GPS antenna is plugged into the sensor and positioned with
unobstructed line of sight to the sky to obtain GPS satellite links. Sensor measurements and
computed outputs can be viewed and recorded with the LORD MicroStrain® MIP Monitor software
that is provided with system starter kits or available as a free download from the LORD
MicroStrain® website. Alternatively, users can write custom software with the LORD MicroStrain®
open source data communication protocol. The data is time-aligned and available by either polling
or continuous stream.
Figure 1 - 3DM-GX4-45™ Sensor
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3DM-GX4™-45™ Inertial Navigation System User Manual
2.1
Sensor Overview
Components
The 3DM-GX4-45™ can be purchased by itself or in a starter kit that include everything needed
to begin using it. The starter kits include the 3DM - GX4 - 45 ™ inertial sensor, a serial
communications cable (either RS232 or USB), a power supply with country plug adapter
(RS232 kits only), an external GPS antenna with a three meter cable, a non-magnetic GPS
antenna adapter cable, and all software, drivers, and documentation. This manual covers all
items included in the starter kits. For a complete list of available configurations, accessories,
additional system products and ordering information see Parts and Configurations on page 65.
Item
A
B
C
D
E
--
--
Description
3DM-GX4-45™ Inertial Sensor
Communications cable (USB or RS232)
Power supply and country plug adapters (for RS232 only)
GPS antenna with attached cable (3m SMA)
GPS antenna cable adapter (non-magnetic MMCX-to-SMA)
MIP Monitor Software Suite
User Manual, Quick Start Guide and Calibration Certificate
Table 1 - Components List
8
Quantity
1
1
1
1
1
1
1
3DM-GX4™-45™ Inertial Navigation System User Manual
2.2
Sensor Overview
Interface and Indicators
The 3DM-GX4-45 ™ sensor interfaces include a dual use communications and power input
connector and a GPS antenna port. The sensor is mounted using the mounting and alignment
holes as needed (see Sensor Mounting on page 47).
The indicators on the 3DM - GX4 - 45 ™ include a device status indicator and the device
information label. Table 2 - Indicator Behaviors describes the basic status indicator behavior.
The device information label includes the sensor frame diagram (axis orientation) which will be
critical during device installation (see Sensor Frame on page 32).
Figure 2 - Interface and Indicators
Indicator
device status
indicator
Behavior
OFF
rapid flash
steady blink
slow pulse
Device Status
no power applied
streaming data with no GPS lock
streaming data with GPS lock
idle mode, awaiting commands
Table 2 - Indicator Behaviors
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3DM-GX4™-45™ Inertial Navigation System User Manual
3.
Basic Setup and Operations
Basic Setup and Operations
Do not bring the inertial sensor into contact or close proximity
with magnets. Magnets may disrupt the sensor operation and
cause magnetization of internal components, which can
affect magnetometer performance. If magnetization is
suspected, use a degaussing tool to demagnetize.
To acquire sensor measurements and computed outputs, the 3DM-GX4-45™ is used with a host
computer capable of serial communication, and a software interface. The LORD MicroStrain ®
MIP Monitor software is provided with the system and includes all functions needed for sensor
configuration and data acquisition. Users may also utilize the LORD MicroStrain ® MIP Data
Communications Protocol to write custom software applications with expanded or specific feature
sets needed for the application. MIP Monitor includes a message building tool that can be used to
streamline this process. For more information see OEM System Integration on page 49.
In this section hardware and software setup is described, including an overview of the MIP Monitor
software menus required to configure a sensor and begin data acquisition. It is intended as a quick
start guide and is not a complete demonstration of all system or software features and capabilities.
Figure 3 - Acquiring Sensor Data with MIP Monitor
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3DM-GX4™-45™ Inertial Navigation System User Manual
3.1
Basic Setup and Operations
Software Installation
NOTE
The MIP Monitor Software Suite includes hardware drivers required for all
3DM-GX4™ sensors. Sensors will not be recognized without these drivers.
To install MIP Monitor Software Suite on the host computer, complete the following steps:
1. Launch the software installation menu by inserting the software CD or thumb drive
into the host computer or by running the Autorun.exe file from the software directory
in Windows® Explorer.
2. In the software installation menu select Install MIP Monitor Software and follow the on
screen prompts to completion.
3. If the sensor has internal magnetometers, select Install MIP Hard and Soft Iron
Calibration Software and follow the on screen prompts to completion. This is used for
magnetometer field calibration.
4. Select Install Inertial Drivers to install the hardware drivers required for operating the
sensors, and follow the on screen prompts to completion.
5. Install Inertial Manuals, if desired, and reboot the host computer.
Figure 4 - Software Installation Menu
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3DM-GX4™-45™ Inertial Navigation System User Manual
3.2
Basic Setup and Operations
System Connections
Power is applied to the sensor either through a host computer
USB port or an external power supply, such as the one
provided in the RS232 starter kit. Use only power supplies
within the operating range of the sensor or damage or injury
could result. Once power is applied the sensor is on and
active.
To acquire sensor data the following components are needed: 3DM - GX4 - 45 ™ sensor,
communication cable, power cable, as applicable for RS232 communications, GPS antenna,
GPS antenna adapter cable, and a host computer with access to the data acquisition software,
such as LORD MicroStrain® MIP Monitor.
Figure 5 - System Connections
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3DM-GX4™-45™ Inertial Navigation System User Manual
3.3
Basic Setup and Operations
Software Interface
The MIP Monitor software includes a main window with system information and menus, a
device settings window ( see Sensor Settings on page 15 ), and several data monitoring
windows (see Data Monitoring and Recording on page 18).
The main window provides an overview of connected devices. Devices are selected by clicking
on them. A device menu is available by right clicking on the device name, and includes the most
used items from the header row menus ( Figure 6 - Main Window ). The header row menu
includes selections for data sampling, recording, device settings, opening windows, selecting
which open window to view, and advanced features such as selecting the communications
mode. The icon toolbar includes buttons for help menu access, device refresh, and data
sampling and recording (see Data Monitoring and Recording on page 18).
Figure 6 - Main Window
3.3.1
Interactive Help Menu
MIP Monitor also features context-sensitive help menus that provide explanations of the
information and settings as they are hovered over with the computer cursor. This feature is
enabled by selecting the question mark icon or Help button in any window.
Figure 7 - Context Sensitive Help Menu
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3DM-GX4™-45™ Inertial Navigation System User Manual
3.4
Basic Setup and Operations
Sensor Communication
Once power has been applied to the sensor, it is on. The sensor selects the appropriate serial
communication (USB or RS232) on power- up based on which cable is connected. If the
hardware drivers have been installed, communication can be established using the
MIP Monitor software interface.
1. Verify the sensor device status indicator is on. GPS lock is not required to establish
sensor communication.
2. Open the MIP Monitor software.
3. The sensor should appear in the device list automatically when the software is
opened, and includes the device information and communication port assignment
(Figure 8 - Sensor Communication ). If it is not automatically discovered, use the
refresh button to search for the sensor.
Figure 8 - Sensor Communication
NOTE
If data is not actively being exchanged between the sensor and host computer
the status message may display Not Connected. This indicates the port status,
not the sensor availability. When commands are sent to the sensor, the
software will automatically connect to it before sending the message.
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3DM-GX4™-45™ Inertial Navigation System User Manual
3.5
Basic Setup and Operations
GPS Link
NOTE
The GPS antenna requires unobstructed line of sight with the sky in order to
achieve communication with the GPS satellites.
Communication between the GPS receiver and GPS satellites is initiated when the 3DM-GX445 ™ is first powered on. The status indicator on the device will blink differently to show if a
satellite link has been established ( see Interface and Indicators on page 9 ). If no link is
established, the receiver will stop searching and enter an idle state. It will not try to establish the
link again until a GPS data output is enabled and data acquisition is started. At that time the
receiver will attempt to reestablish communication in order to provide the requested GPS data.
The GPS Monitor window in the MIP Monitor software will display the satellite and link statistics
(see Global Positioning System (GPS) Outputs on page 25).
Communication with the satellites is required for proper sensor operation, although some
measurement outputs will be available without them.
3.6
Sensor Settings
Device settings are stored in the sensor memory. Only the configuration options that are
available for the type of sensor being used will be available in the configuration menus.
To enter the settings menu, right-click on the sensor name, and select Device Settings from the
menu (Figure 9 - Device Settings Menu).
NOTE
When selecting sensor and estimation outputs to be recorded,
communications bandwidth considerations should be taken into account,
especially when using RS232 communications. Lower baud rates equate to
lower communications bandwidth which can be consumed quickly by selecting
a large number of measurements at high sample rates. Overrunning the
communications bandwidth will result in dropped communications packets and
lost data.
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3DM-GX4™-45™ Inertial Navigation System User Manual
Basic Setup and Operations
1. The following describes the Device Settings interface:
a. Main menu tabs: The main tabs break up the setting into broad
functional groups for the types of measurement available. For the 3DMGX4-45 ™ these will include calculated measurements (Estimation Filter),
GPS metrics (GPS), and direct inertial sensor measurements (IMU).
b. Message Format (first sub-menu tab): Under each main menu tab
there are additional sub-menu tabs, including the Message Format tab.
The Message Format tabs allows the user to select the measurement type
to be displayed and recorded (b1), and the data rate (rate at which data is
sent to the host computer) in samples/second (b2).
c. Measurement parameters (other sub- menu tabs): Available submenu tabs besides the Message Format tab depend on the selected main
menu tab. These tabs include the configurable settings for each
measurements.
d. Scrolling arrows: are used to navigate to additional sub-menus.
e. Help menu: Enable the context sensitive help menu for explanations of
specific settings (see Interactive Help Menu on page 13).
Figure 9 - Device Settings Menu
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3DM-GX4™-45™ Inertial Navigation System User Manual
3.6.1
Basic Setup and Operations
Saving Configurations
Sensor settings are saved temporarily in the device memory by selecting the OK button in
the Device Setup window. To save the settings for future use, select Settings > Save
Current Settings from the main window (Figure 10 - Save Sensor Settings). If the settings
are not saved in this manner they will be lost when the sensor is powered off. If the sensor
settings are saved as described, the setting will remain intact when the sensor is powered
on again.
Previously saved settings can be recalled by selecting the sensor in the device list and the
selecting Settings > Load Startup Settings.
Figure 10 - Save Sensor Settings
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3DM-GX4™-45™ Inertial Navigation System User Manual
3.7
Basic Setup and Operations
Data Monitoring and Recording
NOTE
During viewing and recording, only the outputs that are selected in the
Message Format tabs in the Device Setup menu are displayed and recorded
(see Sensor Settings on page 15).
Throughout the MIP Monitor menus the same icons are used to control data streaming
(sampling) and recording, shown in Table 3 - Sampling and Recording Controls. These icons
can be found in the MIP Monitor main window icon toolbar and in each data monitoring window.
The same commands are also found in the main window Control menu.
Figure 11 - Main Window Controls
Icon
Command
Run: start data streaming
Stop: end data streaming
Step: sample single set of data
Record: start and stop data recording
Table 3 - Sampling and Recording Controls
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3DM-GX4™-45™ Inertial Navigation System User Manual
Basic Setup and Operations
There are several data monitoring views available depending on what measurements are
desired for monitoring and recording. Each view corresponds to one of the main categories in
the Device Settings window. For example, the 3DM - GX4 - 45 ™ includes Sensor Data
Monitoring for the IMU measurements, GPS Monitoring for the GPS metrics, and
EF Monitoring for the Estimation Filter outputs (Figure 12 - Data Monitoring and Streaming ).
During viewing and recording only the outputs that are selected in the Message Format tab of
the Device Settings menu are displayed and recorded (see Sensor Settings on page 15).
Data streaming must be started before data can be recorded, however it is not necessary to be
viewing it in a data monitoring window. Data monitoring is used primarily to confirm the system
is operating correctly or to view the outputs in near real time. If sensor setup has already been
confirmed, streaming and recording can be initiated from the main window.
Figure 12 - Data Monitoring and Streaming is an example of Sensor Data Monitoring, which
displays the selected IMU measurements. In data monitoring windows, no data will be
displayed until data streaming is started, and no data will be recorded (even if it is being viewed)
until data recording is initiated (armed). In this example, the y-axis of the graph indicates data
points and the x-axis is the measurement units, and there is a tab for each measurement.
1. Right-click on the device in the main window and select Sensor Data Monitoring.
2. Press the Start Streaming icon to start sampling.
Figure 12 - Data Monitoring and Streaming
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3DM-GX4™-45™ Inertial Navigation System User Manual
Basic Setup and Operations
3. To record data, select the Arm Recording icon at any time.
4. Select the type of data file to generate, Binary or CSV. The CSV file is the most
common and can be viewed and processed by data editors such as Microsoft Excel ®.
NOTE
If the data is recorded in Binary format it will require a translation program that
utilizes the LORD MicroStrain ® MIP Data Communications Protocol to make it
user-readable.
Figure 13 - Record Data
5. To end recording press the Arm Recording button again, and select OK to the
confirmation prompt.
6. Select the Stop Streaming icon to end sampling.
7. Use the red "X" in the upper right of the sensor monitoring window to exit the
monitoring mode.
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3DM-GX4™-45™ Inertial Navigation System User Manual
3.8
Basic Setup and Operations
Viewing Data
Acquired data is stored in either Binary (.bin) or Comma Separated Values (.CSV) format,
depending on what was selected at the initiation of data recording. The files can be found in the
directory specified at that time or in the default directory on the host computer desktop.
CSV files can be viewed with Microsoft Excel, Quattro Pro, Open Office, or other CSV editors
and spreadsheet programs. Data recorded in Binary format will require a translation program that utilizes the LORD
MicroStrain® MIP Data Communications Protocol to make it user-readable.
Figure 14 - Exploring Data
NOTE
Data in the data files are displayed in time sequence. If measurements are set
to different data rates, not all time intervals will include a reading from each
output that is being recorded.
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3DM-GX4™-45™ Inertial Navigation System User Manual
4.
Sensor Measurements
Sensor Measurements
The 3DM-GX4-45 ™ block diagram (Figure 15 - 3DM-GX4-45™ Block Diagram ) describes its
primary hardware components and internal configuration. Integrated Micro-Electro-Mechanical
System (MEMS) sensors within the 3DM - GX4 - 45 ™ are collectively known as the Inertial
Measurement Unit (IMU) and include tri-axial gyroscopes (gyros), tri-axial accelerometers, tri-axial
magnetometers, and a pressure altimeter. This technology provides direct measurements of
acceleration, angular rate, magnetic field, pressure, delta-Theta (change in acceleration), and
delta- v (change in velocity). Temperature and pressure sensors provide environmental
information for measurement compensation and altitude estimations. GPS information can be
read directly and is also used in the computed navigation estimations.
Computed estimations for position, velocity, and attitude (PVA), and attitude and heading
reference systems (AHRS) are available outputs on the 3DM- GX4 - 45 ™ . To achieve these
estimations, the MEMS sensors are processed by a Navigation (NAV) Estimation Filter (EF)
microprocessor with an Extended Kalman Filter (EKF) . All measurements are temperature
compensated and are mathematically aligned to an orthogonal coordinate system. Additional user
settings such as measurement filtering, biasing, and tolerance values offer adjustments for specific
applications.
Figure 15 - 3DM-GX4-45™ Block Diagram
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3DM-GX4™-45™ Inertial Navigation System User Manual
4.1
Sensor Measurements
Direct Sensor Measurements (IMU Outputs)
The sensors in an Inertial Navigation System (INS), from which measurements for navigation
and orientation are obtained, are collectively know as the Inertial Measurement Unit (IMU).
These sensors are arranged on the three primary axes (x, y, and z) to sense angular rate,
acceleration, and the local magnetic field . The gyroscopes are used to adjust the current
attitude estimate when an angular rate is sensed. The accelerometers sense gravity as well as
linear acceleration. The magnetometers sense the Earth’s magnetic field along with local
magnetic anomalies.
The IMU sensors can be read directly to report stand alone inertial measurements. Because
the sensor system is digital, the analog voltage readings from the sensors are converted into a
digital equivalent value based on the volt-to-bit scale of the internal analog to digital voltage
converter (A/D converter). For example, a 16-bit system will have 65536 A/D values (bits)
applied over the output voltage range of the sensor, typically splitting it in the middle for positive
and negative going signals (+/- 32768 bits). In the MIP Monitor software the conversion values
are not configurable, but there are user settable options for how the measurement is made.
These setting are available in the Settings > Device > IMU (tab). The context sensitive Help
menus (accessed with the Help button) provides explanations of the settings when hovered
over (Figure 16 - IMU Settings).
Figure 16 - IMU Settings
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3DM-GX4™-45™ Inertial Navigation System User Manual
Sensor Measurements
Table 4 - IMU Measurements lists the IMU measurements available for the 3DM-GX4-45 ™ .
Engineering units are temperature compensated, A/D bit readings are not.
Calibration of the 3DM-GX4-45™ IMU sensors is performed at the factory when the device is
manufactured. Calibration values are saved in the device memory (see IMU Sensor Calibration
on page 46).
To view and record IMU outputs, see Basic Setup and Operations on page 10.
Measurement
Units
Gyroscope
gravitational force (g)
Magnetometer
Gauss (G)
Angular Rate
Delta Angle (theta)
degrees/second
radian/second
degrees
radians
Delta Velocity
g*seconds
GPS Correlation Timestamp
weeks, seconds, and
status indicators
Ambient Pressure
milli-bars
Description
three axis acceleration readings in
engineering units
three axis magnetic field readings in
engineering units
three axis rotational velocity reading
from gyroscope in engineering units
time integral of angular rate with
configurable time period
time integral of acceleration with
configurable time period
time metrics from the GPS receiver for
tracking IMU sensor data
air pressure reading from
pressure sensor (displayed in EF data
monitor, see Computed Outputs (Estimation Filter/PVA) on page 27)
Table 4 - IMU Measurements
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3DM-GX4™-45™ Inertial Navigation System User Manual
4.2
Sensor Measurements
Global Positioning System (GPS) Outputs
The Global Positioning System (GPS) receiver in the 3DM - GX4- 45 ™ uses its own GPS
positioning engine to process GPS metrics from a minimum of four satellites. Accuracy and
reliability of the GPS readings are highly dependent on the quality of the satellite fix, and
information is provided to determine an appropriate confidence level. External aiding systems,
such as Wide Area Augmentation System (WAAS) in the US, help compensate for certain
error sources that can affect GPS accuracy. Position of the antenna is also an important
consideration (see GPS Antenna Installation on page 48)
Readings and information are available directly from the GPS receiver. Table 5 - GPS Outputs
describes the available outputs. GPS reporting and recording can be enabled in the
MIP Monitor software through the Settings > Device > GPS (tab) (Figure 17 - GPS Settings).
To view and record GPS outputs, see Basic Setup and Operations on page 10.
Figure 17 - GPS Settings
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3DM-GX4™-45™ Inertial Navigation System User Manual
Measurement
Units
Position (LLH)
degrees (position)
meters (accuracy)
GPS Time
meters/second
(velocity)
meters (accuracy)
weeks & seconds
Position (ECEF)
meters
Velocity (NED)
Velocity (ECEF)
Speed
meters/second
(velocity)
meters (accuracy)
meters/second
(speed)
meters (accuracy)
Description
position reported by GPS module only,
expressed in Latitude, Longitude, and Height
(LLH) with accuracy estimation
velocity measurement reported by GPS module
only, with reference to North, East, Down
coordinate system and with accuracy estimation
time acquired from the satellites
position reported by GPS module only, with reference to the Earth Centered, Earth Fixed
(ECEF) Cartesian coordinate system
velocity reported by GPS module only, with reference to the Earth Centered, Earth Fixed
(ECEF) Cartesian coordinate system
speed along direction of travel in 2D and 3D
space as reported by GPS module only
---
Dilution of Precision (DOP) ratings for accuracy
of GPS readings
Coordinated Universal Time (UTC) to fractional
seconds with leap year seconds adjustment and
confidence indicator. Also week number, month,
date and year.
clock accuracy metrics
information about the type, quantity and quality
of the satellite connections
referred to as Satellite Info, includes satellite
number and signal strength
operational status of GPS receiver and antenna
Individual satellite signal strength indicator
--
(future use)
DOP Data
--
UTC Data
time and date
Clock Information
GPS Fix
Information
Space Vehicle
Information (SVI)
Hardware Status
DGPS Information
DGPS Channel
Status
seconds
-N/A
Height
meters
Heading (NED)
degrees
elevation or altitude relative to average sea level
(MSL reading) or height relative to WSG-84
Ellipsoid (AE reading)
heading reported by GPS module only, with
reference to the North, East, Down coordinate
system and with accuracy estimation
Table 5 - GPS Outputs
26
Sensor Measurements
3DM-GX4™-45™ Inertial Navigation System User Manual
4.3
Sensor Measurements
Computed Outputs (Estimation Filter/PVA)
The computed outputs are measurements from the 3DM-GX4-45 ™ IMU sensors and GPS
receiver that are processed through an Extended Kalman Filter (EKF) algorithm. Together they
produce high accuracy position, velocity, and attitude (PVA) outputs at high data rates. Refer to
Table 6 - Estimation Filter Outputs for a complete list of outputs.
All computed outputs are determined with reference to the sensor frames ( see Sensor
Reference Frames on page 30). Heading is the direction of travel derived from the GPS and
velocity or magnetometer readings. Position is the coordinate location of the sensor, and
velocity is the rate of change from that position. Attitude is an estimation of the sensor’s
orientation in space and is generated from the sensed acceleration and magnetic field vectors,
and gyroscope outputs. Attitude is reported as roll, pitch, and yaw. All output estimates
represent the orientation of the device relative to the local North, East, Down (NED) frame at a
particular point on the Earth’s surface.
In the MIP Monitor software there are user settable options for how the estimations are made.
These setting are available in the Settings > Device > EF (tab). The context sensitive Help
menus (accessed with the Help button) provides explanations of the settings when hovered
over (Figure 18 - Estimation Filter Settings).
Figure 18 - Estimation Filter Settings
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Sensor Measurements
EF outputs can be viewed and recorded with bias, scale, and uncertainty metrics. Other
information, such as GPS time and device status, are available for reference ( Table 6 Estimation Filter Outputs).
To view and record Estimation outputs, see Basic Setup and Operations on page 10.
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Measurement
Units
Filter Status
--
GPS Time
weeks & seconds
Position (LLH)
degrees (position)
meters (uncertainty)
Velocity (NED)
meters/second
(velocity)
meters (uncertainty)
Attitude
(Euler RPY)
radians
Attitude
(Matrix)
radians
Attitude
(Quaternion)
radians
Acceleration
(Linear and
Compensated)
meter/second2
Angular Rate
(Gyro)
radians/second
Description
indicates the current state of the EF, such
as running or initializing
the GPS time from the GPS receiver
estimated position based on combined
sensors inputs and EF, expressed in Latitude, Longitude, and Height (LLH) with
uncertainly estimation available
estimated velocity based on combined
sensor inputs and EF, with reference to
North, East, Down coordinate system and
with uncertainty estimation available
Euler angles representation of
orientation expressed as roll, pitch and
yaw (RPY), with one-sigma uncertainly
estimation available
Transformation matrix that describes
orientation with reference to the Earth
Centered Earth Fixed (ECEF)
coordinate system
Unit quaternions representation of
orientation with one-sigma uncertainly
estimation available
absolute or linear acceleration readings
with reference to either the sensor or
vehicle frame (depending on settings),
with bias and scale readings, and onesigma uncertainty estimations also available.
angular rate readings with reference to
either the sensor or vehicle frame
(depending on settings), with gyro bias
and scale readings, and one-sigma
uncertainty estimations also available.
3DM-GX4™-45™ Inertial Navigation System User Manual
Measurement
Units
Gravity Vector
meter/second2
WSG-84 Local
Gravity Magnitude
meter/second2
Heading Update
radians
WMM (Magnetic
Model Solution)
Gauss
Pressure Altitude
meters (altitude)
pressure (milli-bars)
temperature (°C)
density (kg/m3)
Antenna Offset
Error
--
Sensor Measurements
Description
gravity estimate from accelerometer readings with reference to either the sensor or
vehicle frame (depending on settings)
local magnitude of gravity with reference
to the WSG-84 model and readings from
GPS, valid for altitude.
heading value relative to True North with
one-sigma uncertainly estimation.
World Magnetic Model (WMM) Local
Intensity estimate from magnetometers
and GPS
altitude estimate based on barometric
pressure, air temperature and density,
with available correction based on the
U.S. Standard Atmospheric Model (SAM)
describes the error as a result of the GPS
antenna length and position. Can be mitigated by entering measurements into the
device settings.
Table 6 - Estimation Filter Outputs
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4.4
Sensor Measurements
Sensor Reference Frames
4.4.1
Geodetic Frame
The World Geodetic System is the standard for cartography and navigation. The latest
revision, WGS84, is the reference coordinate system for GPS, and the 3DM- GX4-45 ™
reports position using this coordinate frame. It also calculates the magnitude of the local
gravity vector using the WGS84 reference formulas.
The WGS coordinates are latitude (φ), longitude (λ), and height (h) above the reference
ellipsoid. Latitude ranges from -90 degrees at the South Pole to 90 degrees at the North
Pole. Longitude ranges from -180 to 180 degrees, with 0 degrees being the prime meridian.
The -180/180 degree switchover occurs in the middle of the Pacific Ocean and includes a
section of the International Date Line. The model takes into account the oblateness of the
Earth’s surface.
A point (P) on or above the Earth in the WGS84 coordinate system is notated as: latitude
(φ), longitude (λ), and height above the reference ellipsoid (h).
Figure 19 - World Geodetic System (WGS84) Reference Ellipsoid
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3DM-GX4™-45™ Inertial Navigation System User Manual
4.4.2
Sensor Measurements
North East Down (NED) Frame
The North, East, Down (NED) frame is a local coordinate frame which is formed by a
tangent plane located at a particular point (current coordinates) on the WGS84 reference
ellipse. The NED frame is constructed with the (true) North vector along the line of
longitude, the East vector along the line of latitude, and the Down vector normal to and
towards the tangent plane (Figure 20 - North East Down Frame). The assumption when
using the NED frame is that the local surface can be reasonably approximated by a flat
plane. For most applications, this assumption is valid and provides a more intuitive reference
frame for expressing velocity and attitude information than a global frame.
The 3DM-GX4-45™ reports velocity in this frame and attitude with respect to this frame.
Figure 20 - North East Down Frame
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4.4.3
Sensor Measurements
Sensor Frame
The sensor frame is indicated on the top of the device and is oriented such that the x-axis
vector is parallel with the long side of the sensor and points toward the sensor connector,
the y-axis is 90° to the right of the x-axis, and the z-axis goes through the bottom of the
sensor (outward). These axes were selected so that when the connector on the device is
pointed true north and the device is upright and level, the sensor frame will match the NED
frame exactly, giving zero rotation.
The 3DM-GX4 -45 ™ reports acceleration, angular rate, delta-Theta, delta-velocity, and
sensor biases in this frame.
The sensor frame can be viewed in the MIP Monitor software through the View > 3D
Attitude menu. This window displays the orientation of the sensor in relationship to true
north and shows measurement origination for acceleration and angular rate. The view can
be rotated for clicking, holding, and dragging the image.
Figure 21 - Sensor Frame
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4.4.4
Sensor Measurements
Platform Frame
The 3DM-GX4-45 ™ includes the option to define an orientation transformation and offset
distance from the sensor frame to the platform the sensor is mounted to. This is useful when
the sensor cannot be mounted in the same location or orientation as the desired reference
point on the platform frame. The transformation from sensor to platform frame is defined
with Euler angles and is expressed as a rotation from the sensor frame to the platform
frame. The offset is the location of the origin of the platform reference frame with respect to
the origin of the sensor frame, expressed in the sensor frame.
In the following example (Figure 22 - Platform Frame Transformation) the user has defined
the desired reference point on the platform frame to be located at the front bumper of the
vehicle. In accordance with aircraft co-ordinate systems the vehicle frame is oriented with
the x-axis pointed in the forward direction of travel, the z-axis pointed down, and the y-axis
pointed towards the passenger side. The sensor has been mounted face down toward the
rear of the vehicle, two meters from vehicle reference location with no offset in the y-axis
and z-axis directions. The proper transformation in this example would be: 180 degrees roll,
0 degrees pitch, and 0 degrees yaw, with an offset of [+2, 0, 0] meters (listed as x,y,z).
Figure 22 - Platform Frame Transformation
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Sensor Measurements
In the MIP Monitor software the transformation and offset settings are entered in the
Settings > Device > Estimation Filter > Mounting > Mounting Orientation and Mounting
Offset fields (Figure 23 - Platform Frame Settings).
Figure 23 - Platform Frame Settings
The orientation transformation affects the following EF outputs (see Computed Outputs
(Estimation Filter/PVA) on page 27 ): Attitude, Position (LLH), Acceleration (Linear),
Angular Rate, and Gravity Vector.
The offset affects the following EF output: Position (LLH).
IMU sensor outputs ( see Direct Sensor Measurements (IMU Outputs) on page 23 ) are
always expressed in the sensor frame and are unaffected by the platform frame
transformation or offset. Additionally the transformed acceleration is expressed at the
location of the sensor but within the platform frame. For example, if the sensor is offset from
the center of gravity (CG), and the platform is undergoing a rotation, an acceleration (in
addition to any linear acceleration of the CG) will be sensed in accordance with the following
formula: (tangent acceleration) = (angular rate)*(distance from CG).
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5.
Performance Optimization
Performance Optimization
5.1
Magnetometer Calibration
Although the 3DM-GX4 -45 ™ magnetometers are calibrated at the factory to zero- out any
magnetic influences internal to the device, measurements are still subject to influence from
external magnetic anomalies when the sensor is installed in the user's end application. These
anomalies are divided into two classes: hard iron offsets and soft iron distortions. Hard iron
offsets are created by objects that produce a magnetic field. Soft iron distortions are considered
deflections or alterations in the existing magnetic field. Ideally, these influences are mitigated by
installing the sensor away from magnetic sources, such as coils, magnets, and ferrous metal
structures and mounting hardware. However, often these sources are hard to avoid or are
hidden.
When using the 3DM-GX4-45™ magnetometer to aid in heading estimations, a field calibration
of the magnetometer after final installation is highly recommended. This can be accomplished
using LORD MicroStrain ® MIP Hard and Soft Iron Calibration software. This software is
included with the MIP Monitor Software Suite (see Software Installation on page 11).
The following are instructions for field calibrating the magnetometers.
1. Connect and power-on the sensor as normal.
2. Open the MIP Hard and Soft Iron Calibration software.
3. Select the sensor to be calibrated, and then select Collect Data (Figure 24 - Collect
Calibration Data). The software will begin taking readings, as indicated by the points
counter in the graphing window.
4. As the readings are taken, rotate the sensor or sensor platform in all possible
directions to get a complete profile of the baseline magnetic influences throughout the
sensor frame. Data points will appear on the graph in red. For mobile sensor
platforms, such as ground vehicles, move the platform as much as possible to
simulate actual use without exposing it to excessive magnetic sources (like driving
over railroad tracks or near steel pilings). The intention is to get a baseline value of the
platform in a neutral environment but one that still accounts for the platform itself in all
orientations.
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Figure 24 - Collect Calibration Data
5. When all possible rotations are completed, select Stop Collecting and then select
Save Data to save the calibration data points (Figure 25 - End Calibration).
Figure 25 - End Calibration
6. Select the Spherical Fit or Ellipsoid Fit button, depending on the application.
Spherical Fit is often the best fit for applications with calibration rotations restricted to
a 2D plane. For example, a ground vehicle or a boat because it will not likely not be
rotated on all three axis. Ellipsoid Fit is generally a better correction when soft iron
effects are present, but only if enough data points can be collected in all quadrants. If
the range of motion is restricted in one dimension, the Spherical Fit may be the best
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choice. If there are enough points in all dimensions, the Ellipsoid Fit may be better.
Generally, if the Spherical and Ellipsoid Fits are close in the mean diameter, then the
Ellipsoid Fit will be the best choice.
7. Click Write Spherical Fit or Write Ellipsoid Fit accordingly. This will write the values to
the sensor memory. The soft iron calibration coefficients are displayed in the Device
Iron Cal Matrix fields, and the hard iron calibration coefficients are displayed in the
Offset fields (Figure 26 - Verify Calibration).
8. Test the calibration by first selecting Clear Plot to clearing the graph, and then select
Plot Data to refresh the data points that we just collected. If they do not appear, click
Load Data, and reload them for the saved file.
9. Click Corrected Fit. A Spherical Fit of the data will be plotted. This represents how the
calibration predicts the magnetometer data should look during actual operation.
10. Click Plot Live Data. New data points, represented with green dots, will display the in
the graph. Rotate the device in all orientations, in the same way as during calibration.
Observe the calibration plot (red points) compared to the actual operation plot (green
points) to visualize the accuracy of the calibration (Figure 26 - Verify Calibration).
Calibration and verification is complete.
Figure 26 - Verify Calibration
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5.2
Performance Optimization
Gyroscope Bias
Gyroscope biases (offsets) can be zeroed out to set a baseline value for the static home
position and conditions in the application. This should be done after sensor installation.
To set the gyroscope baseline, place the sensor or sensor platform in the desired home
position. Select Settings > Capture Gyro Bias (Figure 27 - Gyro Bias Capture). The sensor
must remain stationary for about twenty seconds while the outputs are being measured. A
status message will appear when the capture has been completed.
Figure 27 - Gyro Bias Capture
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5.3
Performance Optimization
Heading Drift and Compensation
There are four options for the heading reference source: GPS velocity, the magnetometer, an
external reference, or none. If the setting is an external reference, the user has to provide a
heading reference (for example, see GPS External Receiver on page 54). If the setting is none,
the estimated heading will drift with the drift of the gyroscopes. If the setting is the
magnetometer, there will be no drift, but the accuracy will only be as good as the
magnetometer. If using GPS velocity as a heading reference, the sensor (or sensor platform)
has to be moving, or there will be no heading reading. Moving the platform in a dynamic way will
assist in recapturing the heading (for example, slight s-turns in an aircraft which has been
traveling in a straight line for an extended period of time).
To select between the heading sources in MIP Monitor select Settings > Device > Estimation
Filter > EF Options.
Figure 28 - Heading Source Setting
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5.4
Performance Optimization
Angular Rate and Acceleration Limits
The 3DM-GX4-45™ angular rate and acceleration range depend on the sensors installed in the
device. Exceeding the specified range for either sensor will result in high uncertainty values
from the Estimation Filter until the over-range event is corrected.
5.5
Bandwidth
When selecting sensor and estimation outputs to be recorded, communication bandwidth
considerations should be taken into account, especially when using RS232 serial
communications. Lower baud rates equate to lower communication bandwidth which can be
consumed quickly by selecting a large number of measurements at high sample rates. Severely
overrunning the communication bandwidth can have adverse effects on the sensor
performance due to excessive processor usage. Most computer RS232 ports are limited to
115,200 baud even though the 3DM-GX4-45 ™ is capable of running at 921,600 baud (such as
when using a USB connection).
5.6
Platform Frame Transformation
The transformation from the sensor frame to the platform frame (see Platform Frame on page
33) should be defined to the highest angular accuracy possible. The easiest way to accomplish
this is to co-align the frames. If this is not possible, using a simple transformation, such as 90 or
180 degree rotations on a single axis are preferred. For complex transformations between the
frames, a calibration should be performed or analysis from a model should be conducted.
5.7
GPS Parameters
The GPS receiver used in the 3DM-GX4-45™ has an altitude limitation of 50 kilometers and a
speed limitation of 500 meters/second in accordance with the United States International
Treaty in Arms Regulation (ITAR) restrictions.
To use the 3DM -GX4 - 45 ™ GPS receiver, the external antenna must be connected, and
position with unobstructed light of sight to the sky in order to achieve satellite lock. Operating
environment can also effect GPS operation and it must be operated within operating
specifications.
GPS outages should be kept to a minimum. As the outage period extends above 30 seconds,
errors in the integration of the inertial sensors compound causing the solution to quickly
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Performance Optimization
diverge. Position and velocity errors will grow exponentially with measured acceleration error,
and attitude errors will grow linearly with estimated bias error. Monitoring uncertainty metrics
during GPS outage conditions will provide an indication of the reading reliability.
5.8
GPS Antenna Offset
GPS antenna offset is the distance of the antenna for the GPS receiver in the 3DM-GX4-45™.
This offset effects the accuracy of the GPS position readings. The MIP Monitor allows entry of
the offset in the Settings > Device > Estimation Filter > Mounting > Antenna Offset (Figure 29 GPS Antenna Offset).
For the best possible position accuracy, the GPS antenna offset should be defined to the
highest degree possible, preferably down to the centimeter or millimeter range. Inaccuracies
become non-negligible at 2 to 3 centimeters. The user should strive to minimize this distance as
large offsets (10s of meters or more) will result in position oscillation due to small orientation
inaccuracies. For example, a 1 degree error in attitude with a 10 meter antenna offset would
result in a position error of approximately 0.17 meters. If the offset was only 1 meter, the
position error would be 1.7 cm.
Figure 29 - GPS Antenna Offset
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3DM-GX4™-45™ Inertial Navigation System User Manual
5.9
Performance Optimization
Vehicle Dynamics Mode
The vehicle dynamics mode setting adjusts the Kalman filter expectation of the vehicle’s
motion. By doing this, the filter is better able to account for the effects that different dynamic
platforms have on changes in GPS satellite pseudo-ranges. Each platform setting (portable,
automotive, and airborne) have different velocity and altitude limitations.
In the MIP Monitor software this setting is found in the Settings > Device > Estimation Filter >
EF Options > Vehicle Dynamics Mode menu (Figure 30 - Vehicle Dynamics Setting).
Refer to the 3DM-GX4-45™ Data Communications Protocol (DCP) for more information about
this setting.
Figure 30 - Vehicle Dynamics Setting
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3DM-GX4™-45™ Inertial Navigation System User Manual
5.10
Performance Optimization
Estimation Filter Operation
The 3DM-GX4-45 ™ combines the information from a GPS receiver and the IMU sensors to
calculate a navigation solution that incorporates the strengths of the individual systems while
minimizing their weaknesses.
The GPS solution is bounded and typically very good, but it is susceptible to several error
sources. Due to the geometry of the satellite constellation, vertical position accuracy is typically
less than horizontal position accuracy. Additionally, errors from atmospheric and multipath
effects, as well as clock error, further degrade the accuracy of the solution. Arguably the largest
problem with a GPS-only solution for navigation is that a single GPS receiver cannot give users
the orientation of the platform unless the sensor coordinate frame is co- aligned with the
platform velocity vector. For a lot of applications, this assumption is too restrictive. For example,
the pitch of an aircraft typically does not match the angle the velocity vector makes with the
horizon. This occurs because the aircraft’s wings must be at an angle with the oncoming air to
generate lift. Making the assumption that the two values were the same and using the pitch
angle as an input to an autopilot would be a mistake. In order to obtain the attitude of the
vehicle, something more is needed.
In a conventional Attitude and Heading Reference System (AHRS) several sources of error
exist when making attitude estimates. First, the algorithm assumes the acceleration vector is
dominated by Earth’s gravity, with only transient linear accelerations. When long- duration
linear accelerations are experienced, such as when an aircraft performs a sustained 2G turn,
the AHRS will report incorrect pitch and roll angles. This error is the direct result of the
assumption that the accelerometers are only sensing Earth’s gravity. A second source of error
occurs when the device attempts to measure the Earth’s magnetic field. This field is very weak
compared to the numerous magnetic anomalies typically found in platforms and close to the
Earth’s surface. If the magnetic anomalies in the platform remain constant with respect to the
sensor (no translation or rotation between the two) they can be compensated for by performing
a hard iron and/or soft iron calibration of the magnetometers internal to the 3DM-GX4-45 ™
( see Magnetometer Calibration on page 35 ). The hard iron calibration compensates for
magnetic effects that cause offsets in the magnetic field (additive effects). The soft iron
calibration compensates for effects that cause a non- uniformity of the magnetic field which
results in an ellipsoidal distortion in the field. Non-constant and external sources, such as those
found when traveling through cities, cannot be compensated and may cause large errors in the
heading estimation. Transient errors can be suppressed when the magnetometer readings are
combined with information from the gyroscopes but only for periods on the order of a few
seconds. Longer duration anomalies will result in heading errors. A third source of error occurs
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when attempting to navigate between geographic way- points expressed in latitude and
longitude. This error is due to the difference between detecting magnetic north, which is output
by the AHRS sensor, and true north, which is used to define lines of longitude. If the AHRS is
always used in one geographical location, the user can correct for this difference using a
constant offset. If the AHRS is used over a wide range of longitude, the magnetic declination
must be calculated from a magnetic model or obtained from GPS subsystem which outputs this
data. The greatest problem with an AHRS is that it is an attitude-only device and requires a
GPS for position and velocity.
As a first attempt at an improved navigation solution, a user could get position and velocity from
a GPS receiver and attitude from an AHRS. This is an acceptable solution for many navigation
problems, but is susceptible to most of the errors described above. A more accurate estimation
of position, velocity, and attitude can be found by fusing the data from these two independent
systems using a Kalman filter.
The 3DM-GX4-45 ™ runs a loosely-coupled Extended Kalman Filter. In a loosely-coupled filter,
the inertial sensors in the IMU are used to propagate the state estimation at a high rate (100
Hz); whereas, the GPS position and velocity measurements are used to periodically correct the
state (4 Hz.) This form of Kalman filter is called a sensor fusion filter as it is combining similar
information from multiple sources in a complementary way. This combination takes into
account the statistical properties of the sensors used, providing a better estimate of the true
state than either system individually. The 3DM-GX4-45™ has a full-state dynamics model. The
state propagation utilizes Newton’s and Euler’s equations of motion with the acceleration and
angular rate treated as control inputs. In addition to the GPS measurement, the IMU
magnetometer is available to correct heading mis-alignments which occur during periods of low
dynamics. The magnetometer corrections can be disabled for applications where large, nonconstant magnetic interference sources exist, which would impair their use (such as when
mounting the 3DM-GX4-45™ on a gimbal close to the frame of a ground vehicle).
The Kalman filter estimates the full states of position, velocity, and attitude for a total of 25
states: 3 position, 3 velocity, 4 attitude (quaternion), 3 accel bias, 3 gyro bias, 3 accel scale
factor, 3 gyro scale factor, and 3 GPS antenna offset error states. The bias states are
estimated in order to compensate for the time- varying biases inherent in MEMS inertial
sensors, which are the largest error sources for these devices. The bias states are subtracted
from the gyro inputs, thus providing more accurate inertial data to the propagation stage of the
filter. This enhances overall accuracy and is especially useful during GPS outage conditions.
The Kalman filter also provides statistical information about the quality of the estimated states
described in a covariance matrix. The diagonal terms of the matrix are the variance of each
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Performance Optimization
state, thus the square root of these values are 1-sigma standard deviations. These values give
the filter’s estimation of how well it knows the individual states, given what it knows about the
statistical properties of the noise sources of the various sensors, and also provide feedback to
the user as uncertainty values. The GPS position and velocity noise are not white but are
treated as such in a loosely-coupled filter. This approximation results in not desirable, but the
advantages of this type of filter outweigh that disadvantage.
5.11
Estimation Filter Convergence
5.11.1
Initial Convergence
After a successful initialization, a period of convergence for the Kalman filter states occurs.
Position, velocity, roll angle, and pitch angle typically converge very quickly. Heading,
accelerometer bias, and gyro bias will take more time to converge. If the initial attitude
estimate provided to the filter is well outside of the true attitude, the filter may diverge and
never recover. This is most likely to occur for the heading estimate when a poor value is
used for initialization and when the vibration environment is strong. Should this occur, it is
recommended that the filter is reset and a new attitude estimate is provided. Refer to the
3DM- GX4 - 45 ™ MIP DCP Manual for the various ways of providing an initial attitude
estimate through a user designed interface.
5.11.2
Bias Convergence
Accurate estimation of the biases can take several minutes to converge, therefore after the
filter is initialized, the free- inertial performance will continue to improve until the bias
estimations settles. The MEMS sensor manufacturers quote bias drift stability numbers
which correspond to the expected drift in bias while the sensor is operating. The filter
attempts to track the changing biases over time, and a user can expect these bias estimates
will be non-constant during a navigation run.
5.11.3
Output Uncertainty
The 3DM-GX4-45 ™ estimation data set includes a filter status field that contains a set of
status flags. These flags pertain to high covariance values for position, velocity, and attitude.
These flags should be monitored and cross-check against the corresponding uncertainty
fields when they appear. This can assist in determining how trustworthy the solution
generated by the Kalman filter is. When the filter is first initialized, it is likely that some of
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Performance Optimization
these values will be beyond limits and the flags may be asserted. This fact should be taken
into account when developing automated monitoring systems.
5.12
Vibration Isolation
The 3DM-GX4- 45 ™ should be isolated from strong vibrations a much as possible. Strong,
continuous vibrations appear as unaccounted noise to the estimation filter, degrading its
performance.
5.13
IMU Sensor Calibration
All of the sensor internal to the 3DM-GX4-45™ are calibrated when it is manufactured. With the
exception of the magnetometer field calibration (see Magnetometer Calibration on page 35)
recalibration should not be required unless the device has been under conditions that have
exceeded the operating specifications. For example, if the sensor has been exposed to
excessive shock beyond the rated g-force, performance may be compromised. Indications of
internal sensor damage may be seen as measurement offsets or drift when the sensor is in a
neutral motionless position.
5.14
Temperature Compensation
All sensor conversion and calibration formulas include temperature compensation, so all
computed outputs and most of the IMU sensor outputs are automatically adjusted for local
temperature (see Direct Sensor Measurements (IMU Outputs) on page 23 ).
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3DM-GX4™-45™ Inertial Navigation System User Manual
6.
Sensor Installation
Sensor Installation
6.1
Sensor Mounting
The 3DM- GX4- 45 ™ sensor housing is rated for indoor use only, unless used inside of a
protective enclosure. When using the internal GPS receiver, the GPS antenna connector on
the side of the sensor must be accessible.
The sensor has two mounting tabs with holes for fastening. There are two additional holes
used for precise alignment with 2mm dowel pins. One of the holes is slotted to allow for relaxed
pin positioning accuracy. The sensor can be mounted in any orientation, as required for the
application (see Sensor Reference Frames on page 30). The axes are labeled on the face of
the sensor for reference.
Figure 31 - Mounting the Sensor
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3DM-GX4™-45™ Inertial Navigation System User Manual
6.2
Sensor Installation
GPS Antenna Installation
The GPS antenna cable is plugged into the non-magnetic SMA-to- MMCX adapter cable
supplied with the 3DM-GX4-45 ™. The adapter cable is then plugged into the 3DM-GX4-45™
housing (see Interface and Indicators on page 9). The GPS antenna provided with the starter
kits can be mounted by installing two M3 screws into the base of the antenna (Figure 32 GPS Antenna Mounting). Alternate antenna and cables, as well as external GPS receivers,
can be used with the 3DM-GX4-45 ™ when appropriate for the application (see Alternate GPS
Equipment on page 54).
The antenna must be mounted with an unobstructed line of sight to the sky in order to establish
GPS satellite links. This can be accomplished through a window or more optimally by placing
the antenna outdoors. Use the GPS Monitor in the MIP Monitor software to observe satellite
link strength during installation to optimize placement (see Global Positioning System (GPS)
Outputs on page 25 ). For the most accurate GPS readings and EF outputs the antenna
position, with reference to the sensor, should be carefully measured and entered as the
Antenna Offset setting (see GPS Antenna Offset on page 41).
When using GPS antennas with magnetic bases, take care
to not bring the antenna in close proximity to the sensor either
in initial handling or in permanent installation, as it may
disrupt the magnetometers within the 3DM-GX4-45™.
Figure 32 - GPS Antenna Mounting
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7.
OEM System Integration
OEM System Integration
The 3DM-GX4 -45 ™ starter kits come with everything that is needed for sensor configuration,
operation, and data collection. However, many applications will require custom solutions because
of physical or environmental constraints, required sensor output processing, or for integration into
control systems that react to the sensor outputs. For these applications the 3DM-GX4-45 ™ is
available as a stand-alone component with optional interface connectors. The communication
protocol used for configuring and acquiring sensor data and estimations outputs is available for
these applications as well.
This section describes the 3DM-GX4-45™ hardware connections and an overview of the LORD
MicroStrain® MIP Data Communications Protocol used to write custom software applications.
7.1
Data Communications Protocol (DCP)
The LORD MicroStrain® MIP Data Communications Protocol includes all commands available
for controlling the acquiring data from the 3DM-GX4-45™, including many that are not available
in the MIP Monitor software. Programming is performed through a standard serial interface
program. The programming interface is comprised of a compact set of setup and control
commands and a very flexible user-configurable data output format. The commands and data
are divided into two command sets and one data set corresponding to the internal architecture
of the device. The protocol is packet based. All commands, replies, and data are sent and
received as fields in a message packet. The packets have a descriptor-type field based on their
contents, so it is easy to identify if a packet contains commands, replies, or data.
The LORD MicroStrain ® MIP Data Communications Protocol software developers kit (SDK)
includes sample code can be found on the LORD MicroStrain ® website Support page or by
contacting Technical Support (see Technical Support on page 63).
The 3DM-GX4-45™ MIP DCP Manual describes each command description, message syntax,
message options and provides examples, and can also be found on the LORD MicroStrain ®
website or through Technical Support.
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7.1.1
OEM System Integration
Packet Builder
To expedite program development, a packet builder tool is included in the MIP Monitor
software. The packet builder allows users to send multiple packets to the 3DM-GX4-45 ™
and view the resulting reply data.
Applicable protocol structure and design is described 3DM-GX4-45 ™ MIP DCP Manual.
The manual can be found on the LORD MicroStrain ® website Support page or by
contacting Technical Support (see Technical Support on page 63).
To use the packet builder select Advanced > Packet Builder from the MIP Monitor main
window (Figure 33 - Packet Builder). The sensor must be in the Standard communications
mode to use this feature.
Figure 33 - Packet Builder
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3DM-GX4™-45™ Inertial Navigation System User Manual
7.1.2
OEM System Integration
Sensor Direct Mode
The 3DM-GX4-45 ™ contains two internal sub-systems that can be accessed directly in an
advanced mode (sensor direct mode). When in sensor direct mode, the normal functionality
of the 3DM-GX4-45™ is not available. The sensor direct mode allows programmatic access
of the internal IMU which has its own processor and protocol commands. For more
information about using this mode, contact LORD MicroStrain ® Technical Support (see
Technical Support on page 63).
To enter this mode select Advanced > Communications> Sensor Direct from the
MIP Monitor main window. Once in this mode the device status message will indicate
Sensor Direct Mode (Figure 34 - Sensor Direct Mode).
To exit Sensor Direct Mode select the Refresh button in the MIP Monitor at any time, or use
Advanced > Communication menu to select the Standard operating mode.
Figure 34 - Sensor Direct Mode
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7.1.3
OEM System Integration
GPS Direct Mode
The MIP Monitor software can be used to put the sensor in a mode in which direct access to
the internal GPS receiver is available. In this mode the 3DM-GX4-45™ normal functionality
is not available, and protocol commands cannot be used. This mode is called GPS Direct
mode and is used to allow communication with the receiver through an external utility
program available from the GPS receiver manufacturer (such as u-Blox) or by contacting
LORD MicroStrain® Technical Support (see Technical Support on page 63). Also refer to
the Using u-blox Software Technical Note for specific instructions on that receiver (see
Reference Documents on page 71).
To start communicating with the GPS receiver in GPS Direct mode, select Advanced >
Communication > GPS Direct from the MIP Monitor main window. Once in this mode the
device status message will indicate "GPS Direct Mode" (Figure 35 - GPS Direct Mode).
Figure 35 - GPS Direct Mode
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7.2
OEM System Integration
Sensor Wiring
Only use power supplies within the operating range of the
sensor or permanent sensor damage, or personal injury could
result. There are two input power pins available, each with
different voltage ranges. Connect only one at a time. Observe
connection polarity.
Sensor power and serial communications cables are available from LORD MicroStrain® and
come with the sensor starter kits. These cables will have the micro-DB9 connector on one end
(to connect to the sensor) and either a standard DB9 on the other end (for RS232
communication) or a USB connector (for USB communications). Alternately, the micro-DB9
can be purchased from LORD MicroStrain® with flying leads or the connector by itself can be
purchased from the manufacturer (Ulti-Mate Connector Inc.). See Parts and Configurations on
page 65 for a list of available options.
The connector interface includes connections for USB and RS232 communications (only
connect one), two options for sensor input power range (only connect one), and a precision
hardware timing output (PPS output) for synchronizing with external timestamps. The sensor
selects the appropriate serial communication (USB or RS232) on power-up based on which
connection is used.
Figure 36 - Connector Wiring
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7.3
OEM System Integration
Alternate GPS Equipment
Other (external) GPS receivers, antennas and/or cables can be used with the 3DM-GX4-45™.
When using third party antennas the antenna cable length, antenna gain, and antenna power
must be considered. For antennas with internal LNA (Low Noise Amplifiers) the power
requirements should not have a minimum voltage below 3 volts and the current draw should not
be over 20mA. The longer the cable the lower the signal strength, and including the antenna
cable offset in GPS outputs is advised (see GPS Antenna Offset on page 41). The loss of signal
strength can only be empirically determined by trying out a particular installation and monitoring
the number of satellites links and quality of data reception from those satellites. This can be
done in the MIP Monitor software (see Global Positioning System (GPS) Outputs on page 25).
When using a different GPS antenna, always use the non-magnetic MMCX-to-SMA adapter
supplied with the 3DM-GX4-45™ unless the magnetometer is not used in the end application.
7.3.1
GPS External Receiver
To use an external GPS receiver, the internal one must be disabled and a serial link
established between the receiver and the sensor through the host computer. A program is
then written using the LORD MicroStrain ® MIP Data Communications Protocol to port the
data from the GPS input to the host to the sensor serial port and to translate the
GPS receiver data into the message structure the sensor processor can interpret. The data
cannot be sent any faster than 5Hz.
To set the GPS receiver to external, open the Device Settings menu in the MIP Monitor
software by right-clicking on the sensor name in the main window (Figure 37 - GPS Source
Select). Select the Estimation Filter tab and then EF Options. Set the GPS Update Source
to External GPS .
Test external GPS messaging using the Advanced > GPS External Input interface. This
command will send a fixed external GPS message to the device and mimic a pulse per
second clock input (Figure 38 - External GPS Data).
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3DM-GX4™-45™ Inertial Navigation System User Manual
Figure 37 - GPS Source Select
Figure 38 - External GPS Data
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OEM System Integration
3DM-GX4™-45™ Inertial Navigation System User Manual
7.4
OEM System Integration
Sampling on Start-up
The Save Current Settings command (see Saving Configurations on page 17) can be used to
instruct the sensor to start streaming data as soon as it powered on. This can be useful in
sensor integration applications in which immediate data acquisition is desired. To accomplish
this, data streaming is activated with all desired settings before the Save Current Settings
command. This technique will not work in MIP Monitor because it automatically puts the sensor
in idle mode in order to allow device configuration.
For more information refer to the "Startup Settings" Technical Note on the LORD MicroStrain®
website, or contact LORD MicroStrain® Technical Support (see Technical Support on page
63).
7.5
Connecting to a Datalogger
Many inertial applications incorporate dataloggers, of all different types, to collect and distribute
sensor outputs. For more information and examples refer to the "Using Dataloggers with
Inertial Sensors" Technical Notes on the LORD MicroStrain ® website, or contact LORD
MicroStrain® Technical Support (see Technical Support on page 63).
7.6
Using Wireless Adapters
In some applications it can be very useful to utilize wireless communications from the sensor to
the host computer. One way this can be accomplished by connecting the serial output of the
sensor to a serial to wireless converter, and connecting the wireless receiver to the host
computer. For more information and an example refer to the "Using RS232 Bluetooth
Adapters" Technical Notes on the LORD MicroStrain® website or contact LORD MicroStrain®
Inertial Sensor ProductsTechnical Support (see Technical Support on page 63).
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8.
Troubleshooting
8.1
57
Troubleshooting Guide
Troubleshooting
3DM-GX4™-45™ Inertial Navigation System User Manual
Problem
Troubleshooting
Possible cause and recommended solution
1.1 no power is applied
1. POWER
sensor does not power
on
The status indicator on the device will be off. Apply power to
the device, and the status indicator should illuminate.
1.2 power source is off or miswired
Verify the device power source is connected correctly and
turned on.
1.3 power supply is the wrong voltage
Using a power supply other than the one provided with the
device, or a supply that is outside of the device operating range
could result in permanent damage or cause it to not work
properly.
1.4 sensor is in firmware update mode
Firmware update mode is used when updating firmware on the
device. If the firmware updater fails, it is possible that the device
can get stuck in the firmware update mode. and the sensor will
be non- responsive. Contact LORD MicroStrain ® Technical
Support (See Technical Support on page 63).
1.5 sensor is damaged
If all power settings and connections have been verified, and
the sensor is still unresponsive, contact LORD MicroStrain ®
Technical Support (See Technical Support on page 63).
2.1 sensor not found in MIP Monitor
2. COMMUNICATION
no communication to
sensor or GPS receiver
In MIP Monitor use the Refresh button to look for the sensor
again. If the sensor is still not found try cycling power to it and
trying again.
2.2 communication cable not connected or miswired
Check, remove, and reconnect communications and power
cables as applicable. Replace or rewire as needed.
2.3 device drivers not installed
Verify the drivers are installed on the computer (included with
MIP Monitor Software Suite) and that the software has had
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Problem
Troubleshooting
Possible cause and recommended solution
sufficient time to detect it. See Software Installation on page 11
2.4 serial baud rate setting (not applicable to USB
devices)
The host computer serial port baud rate and the sensor baud
settings must match in order for communication be established.
In MIP Monitor this occurs automatically and the baud rate can
only be changed once initial communication is established. To
change the baud rate in MIP Monitor select Settings > System
and select the desired rate.
NOTE: if the baud rate is set higher than the computer serial
port is capable of reading, communication will be permanently
lost with the device. To recover, it will need to be connected to a
higher speed port, connected via USB cable, or sent to LORD
MicroStrain® for reconfiguration.
2.5 GPS receiver is not communicating
The GPS antenna requires unobstructed line of sight to the sky
in order to link with the GPS satellites. Also verify the GPS
antenna is plugged into the sensor and the cable is intact. Verify
the GPS source setting is set for an internal or external device
as applicable. When using an external receiver, a receiver to
serial translation program that utilizes the LORD MicroStrain®
MIP Data Communications Protocol is required to provide the
GPS data to the sensor.
2.6 sensor or cables are damaged
Verify all connections, power, and settings. If available, try
installing an alternate cable or sensor one at a time to see if the
faulty device can be identified. If no conclusion can be
determined, or to send a device in for repair, contact LORD
MicroStrain ® Technical Support ( See Technical Support on
page 63).
3.1 sampling settings are incorrect
3. DATA ACQUISITION
sensor data is missing
or incorrect
59
If the expected measurements or the sampling rate are
displaying or recorded as expected, enter the Device Settings
menu and verify the sampling settings.
3DM-GX4™-45™ Inertial Navigation System User Manual
Problem
Troubleshooting
Possible cause and recommended solution
3.2 streaming has not started
If data streaming is occurring the sensor device status indicator
will also be flashing to indicate sampling. In MIP Monitor the
device status information field will indicate Streaming. If the
sensor is not streaming data, activate it in the software.
3.3 heading data incorrect
If the magnetometers have not been field-calibrated erroneous
heading data could result. If the GPS antenna offset has not
been entered, or the GPS receiver or satellite link is not
activated, it could also skew heading information.
3.4 sensor data not recorded
Verify data recording has been activated. In MIP Monitor the
device status information field will indicate Recording Data. If
the sensor is not recording, activate it in the software. Verify
specific measurements have been enable for sampling and
recording.
NOTE:Data in the data files are displayed in time sequence. If
measurements are set to different sample rates, not all time
intervals will include a reading from each output that is being
recorded.
3.5 sensor data recorded in binary format
When data recording is started the user can choose between
CSV and Binary output formats. If the data is recorded in
Binary format it will require a translation program that utilizes
the LORD MicroStrain® MIP Data Communications Protocol to
make it human readable.
3.6 sensor has been magnetized
Contact or close proximity with magnets may disrupt the sensor
operation and cause magnetization of internal components,
which can affect magnetometer performance. If magnetization
is suspected, use a degaussing tool to demagnetize.
3.7 sensor is damaged
With the sensor in a static neutral position data look for baseline
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3DM-GX4™-45™ Inertial Navigation System User Manual
Problem
Troubleshooting
Possible cause and recommended solution
offset or drift on the IMU sensor outputs. Sensor damage can
occur as a result of excessive g-force other conditions outside
of its operating specifications.
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8.2
Troubleshooting
Repair and Calibration
General Instructions
In order to return any LORD MicroStrain ® product, you must contact LORD
MicroStrain ® Sales or Technical Support to obtain a Return Merchandise
Authorization(RMA)number. All returned merchandise must be in the original
packaging including manuals, accessories, cables, etc. with the authorization
(RMA#) clearly printed on the outside of the package. Removable batteries
should be removed and packaged in separate protective wrapping. Please
have the LORD MicroStrain® model number and serial number, as well as your
name, organization, shipping address, telephone number, and email. Normal
turn-around for RMA items is 7 days from receipt of item by LORD
MicroStrain®.
Warranty Repairs
LORD MicroStrain ® warrants its products to be free from defective material
and workmanship for a period of one (1) year from the original date of
purchase. LORD MicroStrain ® will repair or replace, at its discretion, a
defective product if returned to LORD MicroStrain® within the warranty period.
This warranty does not extend to any LORD MicroStrain® products which have
been subject to misuse, alteration, neglect, accident, incorrect wiring, misprogramming, or use in violation of operating instructions furnished by LORD
MicroStrain ® . It also does not extend to any units altered or repaired for
warranty defect by anyone other than LORD MicroStrain®.
Non-Warranty Repairs
All non- warranty repairs/replacements include a minimum charge. If the
repair/replacement charge exceeds the minimum, LORD MicroStrain ® will
contact the customer for approval to proceed beyond the minimum with the
repair/replacement.
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8.3
Troubleshooting
Technical Support
There are many resources for product support found on the LORD MicroStrain ® website
including technical notes, FAQs, and product manuals.
http://www.microstrain.com/support_overview.aspx
For further assistance our technical support engineers are available to help with technical and
applications questions.
Technical Support
[email protected]
Phone: 802-862-6629
Toll Free: 800-449-3878
Fax: 802-863-4093
SKYPE: microstrain.orientation.support
Live Chat is available from the website during business hours:
9:00 AM to 5:00 PM (Eastern Time US & Canada)
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9.
Maintenance
Maintenance
There are no user-serviceable parts on the 3DM-GX4-45 ™ . Removing the device cover or
disassembling in any way will void the product warranty.
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10.
Parts and Configurations
Parts and Configurations
10.1
Standard Configurations
For the most current product information, custom, and OEM options not listed below, refer to
the LORD MicroStrain® website or contact the LORD MicroStrain® Sales Department.
Table 7 - Model Numbers describes the standard models available at the time this manual was
published. Once a model is selected, the part number is further defined by desired configuration
and interface options. The model determines the first four digits of the product part number
while the options are indicated in the last four digits (Figure 39 - Standard Part Numbers).
Table 7 - Model Numbers
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3DM-GX4™-45™ Inertial Navigation System User Manual
Parts and Configurations
The same options are available in each model, and are indicated in the last four digits of the
product part number. For a list of the starter kit contents, see Components on page 8.
Figure 39 - Standard Part Numbers
Description
LORD MicroStrain®
Part Number
3DM-GX4-15 Starter Kit (RS232, +/-5g, 300°/sec)
3DM-GX4-15 Starter Kit (USB, +/-5g, 300°/sec)
3DM-GX4-25 Starter Kit (RS232, +/-5g, 300°/sec)
3DM-GX4-25 Starter Kit (USB, +/-5g, 300°/sec)
3DM-GX4-45 Starter Kit (RS232, +/-5g, 300°/sec)
3DM-GX4-45 Starter Kit (USB, +/-5g, 300°/sec)
6233-4221
6233-4241
6234-4221
6234-4241
6236-4221
6236-4241
Table 8 - Example Part Numbers
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10.2
Parts and Configurations
Accessories
The following parts are available for use with the 3DM-GX4™ and some are included in sensor
starter kits. For the most current product information refer to the LORD MicroStrain® website or
contact the Sales Department. See Sales Support on page 69.
Description
LORD MicroStrain®
Part Number
RS232 communications cable
USB communications cable
RS232 power supply
RS232 power supply country plug adapter kit
Gilsson GPS patch antenna with 3m cable
Antenna cable adapter MMCX to SMA
MIP Monitor Software Suite flash drive
Sensor mating connector (micro-DB9) with flying leads
4005-0037
9022-0019
9011-0009
9011-0022
9100-0100
9022-0032
8200-0020
6224-0100
Table 9 - Sensor Accessories
Description
Ulti-Mate Connector
Inc. part number
“A” Series or “P” Series 9-pin male Micro-D connector
PR09N05
Table 10 - Sensor Mating Connector
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10.3
Parts and Configurations
Warranty Information
Warranty
LORD MicroStrain ® warrants its products to be free from defective material
and workmanship for a period of one (1) year from the original date of
purchase. LORD MicroStrain ® agrees to repair or replace, at its sole
discretion, a defective product if returned to LORD MicroStrain ® within the
warranty period and accompanied by proof of purchase. This warranty does
not extend to any LORD MicroStrain ® products which have been subject to
misuse, alteration, neglect, accident, incorrect wiring, mis-programming or to
use in violation of operating instructions furnished by LORD MicroStrain ® . It
also does not extend to any units altered or repaired for warranty defect by
anyone other than LORD MicroStrain ® . This warranty does not cover any
incidental or consequential damages and is in lieu of all other warranties
expressed or implied. No representative or person is authorized to assume for
LORD MicroStrain ® any other liability in connection with the sale of LORD
MicroStrain ® products. Some states do not allow limitations on how long an
implied warranty lasts, and/or the exclusion or limitation of incidental or
consequential damages, so the above limitations and exclusions may not apply
to the original customer.
Terms and Conditions of Sale
Please refer to the LORD MicroStrain ® website Support page for
complete Terms and Conditions of product sales.
Terms and Conditions of Service
Please refer to the LORD MicroStrain ® website Support page for
complete Terms and Conditions of product service.
Trial System
To enable customers to try our products risk-free, LORD MicroStrain® offers a
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3DM-GX4™-45™ Inertial Navigation System User Manual
Parts and Configurations
30-day return policy on the purchase of a starter kit. In order to take advantage
of this offer, a purchase order or payment for the starter kit is required when
the order is placed. If the product is not suited to the application, the product
may be returned within 30 days from the date of receipt for a full refund
(excluding shipping and handling), as long as the product is unaltered and
undamaged. Items can only be returned after LORD MicroStrain ® has issued
an Return Material Authorization (RMA). Items must be packed to withstand
shipping, sent via freight, and pre-paid. LORD MicroStrain ® will inspect the
items returned and issue a refund or credit once the items have been
examined and are deemed to be unaltered or undamaged. Non-standard or
custom products may only be returned with approval and a re-stocking penalty
may be assessed. A 30- Day Return must be initiated by receiving a
RMA from LORD MicroStrain®.
10.4
Sales Support
Products can be ordered directly from the LORD MicroStrain ® website by navigating to the
product page and using the Buy feature. http://www.microstrain.com/inertial
For further assistance, our sales team is available to help with product selection, ordering
options, and questions.
Sales Support
[email protected]
Phone: 802-862-6629
Toll Free: 800-449-3878
Fax: 802-863-4093
9:00 AM to 5:00 PM (Eastern Time US & Canada)
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11.
Safety Information
Safety Information
This section provides a summary of general safety precautions that must be understood and
applied during operation and maintenance of components in the LORD MicroStrain ® Inertial
Sensor Products. Throughout the manual, ANSI Z535 standard safety symbols are used to
indicate a process or component that requires cautionary measures.
Situations in which potentially hazardous conditions exist
that could result in death or serious injury of workers and/or
the general public if not avoided.
Situations where a non- immediate or potential hazard
presents a lesser threat of injury that could result in minor or
moderate injury to workers and/or the general public.
Situations where a non- immediate or potential hazard
presents a risk to damage of property and equipment. May
be used to indicate important operational conditions.
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12.
References
References
12.1
Reference Documents
Many references are available on the LORD MicroStrain ® website including product user
manuals, technical notes, and quick start guides. These documents are continuously updated
and may provide more accurate information than printed or file copies. Document
Where to find it
3DM-GX4-45™ Software Developers Kit
http://www.microstrain.com/softwaredevelopment-kits-sdks
http://www.microstrain.com/support/docs
http://www.microstrain.com/support/docs
http://www.microstrain.com/applications
http://www.microstrain.com/wireless/sensors
http://www.nist.gov/calibrations/
http://www.astm.org/Standard/standardsand-publications.html
3DM-GX4-45™ MIP DCP Manual
Product Technical Notes
Product Application Notes
Product Datasheets
NIST Calibration Procedures
ASTM Testing Procedures
Table 11 - Document Resources
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12.2
References
Glossary
A
A/D Value
The digital representation of analog voltages in an analog-to-digital (A/D) conversion. The
accuracy of the conversion is dependent on the resolution of the system electronics. Higher resolution produces a more accurate conversion.
Acceleration
In physics,acceleration is the change in the rate of speed (velocity) of an object over time.
Accelerometer
A sensor used to detect and measure magnitute and direction of an acceleration force (g-force)
in reference to its sensing frame. For example, at rest perpendicular to the Earth's surface an
accelerometer will measure 9.8 meters/second squared as a result of gravity. If the device is
tilted the acceleration force will change slightly, indicating tilt of the device. When the accelerometer is moving it will measure the dynamic force (including gravity).
Adaptive Filter
An adaptive filter is a linear filter that contains an optimization algorithm that adapts to dynamic
conditions. These filters are often complex and necessary to compensate for sensor anomalies.
AHRS (Attitude and Heading Reference System)
A navigation device consisting of sensors on the three primary axis used to measure vehicle direction and orientation in space. The sensor measurements are typically processed by an
onboard algorthim, such as an Estimation Filter, to produce a standardized output of attitude
and heading.
Algorithm
In math and science, an algorithm is a step-by-step process used for calculations.
Altittude
The distance an object is above the sea level
Angular rate
The rate of speed of which an object is rotating. Also know as angular frequency, angular
speed or radial frequency. Typically measured in radians/second.
API (Applications Programming Interface)
A library and/or template for a computer program that specifies how components will work
together to form a user application. For example, how hardware will be accessed and what
data structures and variables will be used.
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References
ASTM (Association of Standards and Testing)
A nationally accepted organization for testing and calibration of technological devices
Attitude
The orientaion of an object in space with reference to a defined frame, such as the North, East,
Down (NED) frame
Azimuth
A horizontal arc measured between a fixed point (such as true north) and the vertical circle
passing through the center of an object
B
Bias
A non-zero output signal of a sensor when no load is applied to it, typically due to sensor imperfections. Also called offset.
C
Calibration
To standardize a measurement by determining the deviation standard and applying a correction, or calibration, factor
Configuration
A general term applied to the sensor indicating how it is set up for data acquisition. It includes
settings such as sampling rate, active measurements, measurement settings, offsets, biases,
and calibration values
Convergance
When mathematical computations approach a limit or a solution that is stable and optimal.
D
Data Acquisition
The process of collecting data from sensors and other devices
Data Logging
The process of saving acquired data to the system memory, either locally on the device, or
remotely on the host computer.
Data rate
The rate at which sampled data is transmitted to the host.
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3DM-GX4™-45™ Inertial Navigation System User Manual
References
Delta-Theta
The time integral of angular rate expressed with refernce to the device local coordinate system,
in units of radians.
Delta-velocity
The time integral of velocity expressed with refernce to the device local coordinate system, in
units of g*second where g is the standard gravitational constant.
E
ECEF
Earth Centered Earth Fixed is a reference frame that is fixed to the earth at the center of the
earth and turning about earth's axis in the same way as the earth.
Estimation Filter
A mathematical algorithm that produces a statistically optimum solution using measurements
and references from multiple sources. Best known estimation filters are the Kalman Filter and
Extended Kalman Filter.
Euler angles
Euler angles are three angles use to describe the orientation of an object in space such as, the
x, y and z or pitch, roll, and yaw. Euler angles can also represent a sequence of three elemental
rotations around the axes of a coordinate system.
G
GPS (Global Positioning System)
A network of space based statellites use to triangulate position co-ordinates and provide time
information for navigational purposes.
Gyroscope
A device used to sense angular movements such as rotation.
H
Heading
An objects direction of travel with reference to a co-ordinate frame, such as lattitude and longitude.
Host (computer)
The host computer is the computer that orchestrates command and control of attached devices
or networks.
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References
I
IMU
Inertial Measurement System
Inclinometer
Device used to measure tilt, or tilt and roll.
Inertial
Pertaining to systems that have inertia or are used to measure changes in inertia as in angular
or linear accelerations.
INS (Inertial Navigation System)
Systems that use inertial measurements exclusively to determine position, velocity, and attitude
given an initial reference.
K
Kalman Filter
An algorithm that processes sensor data or other input data over time, factoring in underlying
noise profiles by linearizing the current mean and covariance to make statistically optimal estimations of what the actual measurements should be.
L
LOS (Line of Sight)
Line of Sight is an acronym used in wireless communications that describes the ideal condition
between transmitting and receiving devices in a wireless network. As stated, it means they are
in view of each other with no obstructions.
M
Magnetometer
A type of sensor that measures the strength and direction of the local magnetic field with
refernce to the sensor frame. The magnetic field measured will be a combination of the earth's
magnetic field and any magnetic field created by nearby objects.
MEMS (Micro-Electro-Mechanical System)
The technology of miniaturized devices typically made using micro fabrication techniques such
as nanotechnology. The devices range in size from one micron to several millimeters and may
include very complex electromechanical parts.
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N
NED
North, East, Down. A geographic reference system
O
OEM
Original Equipment Manufacturer
Offset
A non-zero output signal of a sensor when no load is applied to it typically due to sensor imperfections. Also called bias.
Orientation
The orientaion of an object in space with reference to a defined frame. Also called attitude.
P
Pitch
In navigation pitch is what occurs when vertical force is applied at a distance forward or aft from
the center of gravity of the platform, causing it to move up or down with respect to the sensor or
platform frame origin.
Position
The spatial location of an object
PVA
Position Velcoity and Attitute
Q
Quaternion
Mathematical notation for representing orientation and rotation of objects in three dimensions
with respect to the fixed earth coordinate quaternion. Quaternions convert the axis–angle representation of the object into four numbers and to apply the corresponding rotation to a position
vector representing a point relative to the origin.
R
Resolution
In digital systems, the resolution is the number of bits or values available to represent analog
voltages or information. For example, a 12-bit system has 4096 bits of resolution and a 16-bit
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system has 65536 bits.
RMS
Root Mean Squared
Roll
In navigation roll is what occurs when a horizontal force is applied at a distance right or left from
the center of gravity of the platform, causing it to move side to side with respect to the sensor or
platform frame origin.
RPY
Roll, Pitch and Yaw
RS232
A serial data communications protocol
S
Sampling
The process of taking measurements from a sensor or device.
Sampling rate
Rate at which the sensors are sampled.
Sampling Rate
The frequency of sampling
Sensor
A device that physically or chemically reacts to environmental forces and conditions and produces a predictable electrical signal as a result
Sigma
In statistics, sigma is the standard deviation from the mean of a data set.
Space Vehicle Information
Refers to GPS satellites
Streaming
Typically when a device is sending data at a specified data rate continuously without requiring a
prompt from the host.
U
USB (Universal Serial Bus)
A serial data communications protocol
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UTC (Coordinated Universal Time)
The primary time standard for world clocks and time. It is similar to Greenwich Mean Time
(GMT).
V
Vector
A measurement with direction and magnitude with refernce from one point in space to another
Velocity
The rate of change of position with respect to time. Also called speed.
W
WAAS (Wide Area Augmentation System)
An air navigation aid developed to allow aircraft to rely on GPS for all phases of flight, including
precision approaches to any airport.
WGS (World Geodetic System)
A protocal for geo-referencing such as WGS-84
Y
Yaw
In navigation yaw is what occurs rotational force is applied at a distance forward or aft from the
center of gravity of the platform, causing it to move around the center axis of a sensor or platform frame origin.
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