Acquisition Final.indd
Algorithmic Closed Loop Controller and
Remote Channel Multifunction DAC
The VT1415A and VT1422A are C-size, single-slot, VXI modules
capable of either multi-function input/output (data acquisition)
or powerful control capabilities. They serve as powerful data
acquisition modules that handle analog input/output and digital
input/output in both static and dynamic modes. The digital
capability includes the ability to set or sense static states, to
measure input frequency and period, to totalize, and to input or
output PWM and FM signals. Refer to the VXI Technology Website
for instrument driver availability and downloading instructions, as
well as for recent product updates, if applicable.
Algorithmic Closed Loop Controller - VT1415A
Powerful Data Acquisition Capability
More powerful than PID controllers and easier to implement than
large custom control systems, the VT1415A fills a unique niche in
the data acquisition and control field, providing both control and
precise data acquisition. Applications include:
Powerful Control Capability
PID control of stimulus loops such as hydraulic actuators,
levers, rotational devices as in structural test
Custom On-board DSP Program
PID control of temperature, position, velocity, acceleration and
Complex control such as cascade loops in thermal cooling
jackets, ratio
Comprehensive On-board Signal
Wide Choice of Input/Output
Signal Types
Large Channel-count Strain Signal
Conditioning and Measurement
Independent loops with multi-level alarms.
The design of the on-board, DSP firmware assures the user that all
inputs, all calculations, and all outputs can be completed between
scan triggers. This means there is no drift, or jitter in the critical
time intervals that are used to calculate integrals and derivatives in
control algorithms.
The firmware allows a user to employ pre-written PID control
algorithms, modify them for specific application needs, or to write
an application from scratch. Low duty-cycle connection to the host
computer allows interaction between the host and real-time DSP
so the user can update algorithms, change tuning constants, or do
envelope control. Limited host computer interaction leads to very
high performance (8-loops, update rate 1000/second per loop with
simple PID calculation included).
Multi-function Data Acquisition & Control Module - VT1422A
The VT1422A is a module that is essentially the same as the
VT1415A and has all of the same data acquisition and control
capabilities as the VT1415A, plus some additional features.
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Algorithmic Closed Loop Controller and
Remote Channel Multifunction DAC
The VT1422A serves as the controller in this system,
managing all the configuration, calibration, triggering of
measurements, EU conversion, and calibration processes.
The main differences between the VT1415A and VT1422A
• The VT1422A has 40 kB of memory available for user
algorithms; the VT1415A has 48 kB.
• If the only thing being done in an application is collection
of strain data, the VT1422A user doesn’t have to write an
algorithm, as for the VT1415A.
• The VT1422A offers the same two Terminal Blocks as does
the VT1415A.
(Option 011 screw terminals and Option 013 spring clamp)
Automated Calibration for Better Measurements
The VT1415A and VT1422A offer superior calibration
capabilities that provide more accurate measurements.
Periodic calibration of the module’s measurement inputs
is accomplished by connecting an external voltage
measurement standard (such as a highly accurate
multimeter) to the inputs of the module. This external
standard first calibrates the on-board calibration source.
Then built-in calibration routines use the on-board calibration
source and on-board switching to calibrate the entire signal
path from the closed loop controller’s input, through the
signal conditioning plug-ons (SCPs) and FET MUX, to the
A/D itself. Subsequent daily or short-term calibrations of
this same signal path can be quickly and automatically
done using the internal calibration source to eliminate
errors introduced by the signal path through the SCPs and
FET MUX or by ambient temperature changes. All input
channels can be quickly and productively calibrated to assure
continued high-accuracy measurements.
In addition to the calibration of the signal paths within the
modules, the VT1415A and VT1422A allow you to perform
a “Tare Cal” to reduce the effects of voltage offsets and IR
voltage drops in your signal wiring that is external to the
module. The Tare Cal uses an on-board D/A to eliminate these
voltage offsets. By placing a short circuit across the signal
or transducer being measured, the residual offset can be
automatically measured and eliminated by the D/A. Tare Cal
should not be used to eliminate the thermoelectric voltage of
thermocouple wire on thermocouple channels.
Flexibility with Deterministic Control
The VT1415A and VT1422A are digital sampling closed loop
control systems that are complete in a single VXI module. All
signal conditioning, process monitoring, control calculations,
and control signals are handled on-board without the need
for computer supervision. Once setup is done, the module is
essentially free-running.
The inputs are updated at the beginning of each cycle and the
outputs are updated at a later deterministic time in the cycle
so that various paths in the control algorithm do not affect
the loop timing. These steps are executed automatically and
deterministically without need for intervention from a system
Other Features
Digital Sampling Closed Loop Control System
The VT1415A/VT1422A combine flexibility with deterministic
control. Control algorithms for each of the loops can be the
default PID calculation or a user-defined, downloaded, custom
algorithm. The loop update rate is deterministically controlled
by an internal clock so that variations in the algorithm
execution times do not affect the loop cycle time.
40 MHz
Engr. Unit
VXI Backplane
The VT1422A Remote Channel Multi-Function DAC Module
supports the VT1539A Remote Channel Signal Conditioning
Plug-on and the VT1529B Remote Strain Signal Conditioning
Unit to form a high-performance, but economical strain
measurement system.
Digital Sampling Closed Loop System
Powerful Control Capability
The control algorithm for each loop is easily developed by the
user from a list of algebraic expressions and flow constructs
such as IF, THEN, ELSE. Tuning is simplified because all of
the constants in the algorithm as well as the algorithm itself
can be updated on-the-fly. New values are double-buffered
so there is no need to stop scanning the inputs or halt the
algorithm execution.
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Algorithmic Closed Loop Controller and
Remote Channel Multifunction DAC
The on-board 40 MHz pipelined DSP provides highly
deterministic execution, making it easy to accurately predict
cycle times. Engineering unit conversions for temperature,
strain, resistance, and voltage measurements are made
automatically without slowing down the algorithm execution
Wide Choice of Inputs/outputs
The inputs to the loop algorithm can be measured values
from multiple channels, operator input values, outputs from
other loops, or values from other subsystems. The VT1415A/
VT1422A have a variety of signal conditioning plug-ons for
making measurements of:
Temperature, strain
Voltage, current, resistance
RPM, frequency, totalize
Discrete levels, TTL, contact closures
In addition, the measured input values and the calculated
output values can be stored in a 64,000-sample FIFO buffer
and efficiently transferred to the controlling computer in
blocks of data. With this feature, it is no longer necessary to
waste resources by dedicating a data acquisition channel to
monitor each control loop input and output. The result of any
algorithm calculation can be an input for use by another loop
or subsystem, or it can be a direct output of several different
types. Among the choices of output are:
Signal Conditioning Plug-Ons
A Signal Conditioning Plug-on (SCP) is a small daughter
board that mounts on VXI Technology’s VXI scanning
measurement and control modules. These SCPs provide a
number of input and output functions. Several include gain
and filtered analog inputs for measuring electrical and sensorbased signals, as well as frequency, total event count, pulsewidth modulation, toothed-wheel velocity, and digital state.
Output functions include analog voltage and current D/As, 8or 16-bit digital outputs, pulse output with variable frequency
and PWM, and stepper motor control.
Refer to the information on each individual SCP for more
Voltage Measurements
Use any of the following SCPs with the VT1415A/VT1422A to
make voltage measurements: VT1501A, VT1502A, VT1503A,
VT1508A, VT1509A, VT1512A, or VT1513A.
Temperature Measurements
Any of the input SCPs can be used to make temperature
measurements with thermocouples, thermistors, or RTDs, but
the VT1503A/VT1508A/VT1509A SCPs provide higher accuracy
with thermocouples.
Resistance Measurements
Analog voltage
Analog current
Discrete levels (TTL)
Pulse width modulation (TTL)
As an example of output flexibility, the pulse width
modulation output has several modes. In the PWM freerun mode, the frequency or pulse width output rate is
independent of the loop update rate and can be changed
once per loop update cycle. The square wave mode provides
a variable frequency, fixed 50% duty cycle output signal.
The pulse-per-update mode provides a variable width pulse
synchronized to the loop update cycle.
Operator Control
Manual control can be implemented through a user software
interface or external hardware, such as a potentiometer.
Seamless transfer from auto to manual mode, or manual to
auto is handled automatically by a set-point-tracking routine
in the default PID algorithm code.
Resistance is measured using either the VT1505A 8-channel
Current Source SCP and an input SCP or the VT1518A 4-wire
Resistance Measurement SCP. Measurements are made by
applying a dc current to the unknown and measuring the
voltage drop across the unknown.
Static Strain Measurements
There are two ways to make static strain measurements.
The VT1506A and VT1507A SCPs provide a convenient way
to measure a few channels of static strain. When using the
VT1506A/VT1507A for bridge completion, a second SCP is
required to make the measurement connection. You can use
the following SCPs for this type of static strain measurements:
• VT1503A 8-channel Programmable Filter/Gain
• VT1506A 8-channel 120 Ω Strain Completion & Excitation
• VT1507A 8-channel 350 Ω Strain Completion & Excitation
• VT1508A 8-channel 7 Hz Fixed Filter & x16 Gain
• VT1509A 8-channel 7 Hz Fixed Filter & x64 Gain
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Algorithmic Closed Loop Controller and
Remote Channel Multifunction DAC
For applications requiring large channel counts of strain
measurement, the EX1629 provides a more cost effective
approach to static (and dynamic) strain measurements.
Dynamic strain measurements are implemented by
connecting the EX1629 to high-speed digitizers, such as the
VXI Technology VT1432B and VT1433B.
Use the VT1533A Digital I/O SCP to provide two 8-bit input/
output words.
Note: SCPs are also available for making dynamic strain
measurements (VXI Technology VT1510A, VT1511A, and
The VT1538A Enhanced Frequency/Totalize/PWM SCP provides
eight (8) channels which can be individually configured as a
frequency or totalizer input, or as a pulse width modulated
Transient Measurements
Compact Packaging with Signal Conditioning
When making higher speed measurements, a vital issue
often is the time skew between channels. Ideally, in many
applications, the sampled data is needed at essentially
the same instant in time. While the intrinsic design of the
VT1415A/VT1422A provides scanning of 64 channels, with
maximum skew of 640 µs between the first and last channel
(far less than most sampled data systems), this still may not
be small enough skew for some applications.
The VT1415A/VT1422A provide for configurable signal
conditioned I/O with up to eight individual plug-ons for
analog, digital, and frequency needs. The SCPs are:
Transient Voltage Measurements
The VT1510A provides basic sample-and-hold capabilities
on four channels. Six-pole Bessel filters provide alias and
alias-based noise reduction while giving excellent transient
response without overshoot or ringing. The VT1510A can
be used in strain applications primarily where the bridge is
Digital I/O
• VT1501A 8-channel Direct Input SCP
• VT1502A 8-channel 7 Hz Low-pass Filter SCP
• VT1503A 8-channel Programmable Filter and Gain SCP
• VT1505A 8-channel Current Source SCP
• VT1506A 8-channel 120 Ω Strain Completion &
Excitation SCP
• VT1507A 8-channel 350 Ω Strain Completion &
Excitation SCP
• VT1508A 8-channel x16 Gain & 7 Hz Fixed Filter SCP
• VT1509A 8-channel x64 Gain & 7 Hz Fixed Filter SCP
Transient Strain Measurements
• VT1510A 4-channel Sample & Hold Input SCP
The VT1511A, a double-wide SCP, has all the capabilities
of the VT1510A but adds on-board bridge excitation and
completion functions. The four direct input channels are used
for monitoring the bridge excitation. A maximum of four SCPs
(16 channels) can be installed on a VT1415A/VT1422A.
• VT1512A 8-channel 25 Hz Fixed Filter SCP
Analog Output
• VT1521 4-channel High-speed Bridge SCP
Use the VT1531A for voltage outputs, and the VT1532A for
current outputs. The VT1531A and VT1532A have eight (8)
output channels available on each SCP.
• VT1532A 8-channel Current Output SCP
A maximum of seven (7) VT1532A SCPs can be installed on
each VT1415A/VT1422A due to power limitations. There are no
power restrictions on the VT1531A.
• VT1538A Enhanced Frequency/Totalize/PWM SCP
• VT1511A 4-channel Transient Strain SCP
• VT1513A 8-channel Divide-by-16 Fixed Attenuator &
7 Hz Low-pass Filter SCP
• VT1518A 4-wire Resistance Measurement SCP
• VT1531A 8-channel Voltage Output SCP
• VT1533A 16-bit Digital I/O SCP
• VT1536A 8-bit Isolated Digital I/O SCP
• VT1539A Remote Channel SCP (VT1422A only)
Product Specifications
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Algorithmic Closed Loop Controller and
Remote Channel Multifunction
Timing Signals
Scan triggers:
Scan-to-scan timing and
timing can be set
Can be derived from a software
command or a TTL level from
other VXI modules, internal timer,
or external hardware.
Typical latency 17.5 µs.
Multiple VT1415A/VT1422A
modules can be synchronized
at the same rate using the TTL
trigger output from one
VT1415A/VT1422A to trigger
the others.
Multiple VT1415A/VT1422A
modules can be synchronized at
different integer-related rates
using the ALG:SCAN:RATIO
command and the TTL trigger
output from one VT1415A/
VT1422A module to trigger
the others.
Scan Triggers
Maximum reading rate:
VT1415A: Up to 56 kSa/s
dependent upon configuration
VT1422A: Up to 25 kSa/s
dependent upon configuration
64 kSamples
Maximum input voltage:
Normal mode plus
common mode
Damage level:
±16 V peak
±42 V peak
Maximum common mode voltage:
Damage level:
SCP input impedance:
±16 V peak
±42 V peak
100 MΩ differential
Maximum tare cal offset: 62.5 mV range ±75% of full
scale, other ranges ±25%
of full-scale
Phase jitter scan-to-scan: 80 ps rms
Phase jitter card-to-card:
41 ns peak 12 ns rms
Measurement Accuracy
100 µs to 6.5536 s
100 µs
Trigger count:
1 to 65535 or infinite
Sample Timer
VT1415A: 10 µs to 32768 ms
VT1422A: 40 µs to 32768 ms
0.5 µs
Typically ±0.01% of input level; varies with the SCP used.
Specifications are 90 days, 23 °C ± 1 °C, with *CAL done after
a 1hr warm-up and CAL:ZERO done within 5 minutes. Note:
Beyond the 5min. limitation and CAL:ZERO not done, apply the
following drift error: Drift = 10 µV/°C ÷ SCP gain, per °C change
from CAL:ZERO temperature.
Accuracy Data
Measurement accuracy is dependent upon the SCP module used.
Refer to the accuracy tables and graphs for the individual SCP to
determine the overall measurement accuracy.
Measurement Specifications
The following specifications include the SCP and scanning
A/D performance together as a unit. Accuracy is stated for
a single sample. Averaging multiple samples will improve
accuracy by reducing noise of the signal. The basic VT1415A
scanning A/D has a full-scale range of ±16 V and five autoranging gains of x1, x4, x16, x64, and x256. An SCP must be
used with each eight channel input block to provide input
protection and signal conditioning.
Many definitions of accuracy are possible. Here we use singleshot with 3 sigma noise. To calculate accuracy assuming
temperature is held constant within ±1 °C of the temperature at
calibration, the following formula applies:
Single Shot 3σ = ±(√((GainError)2 + (OffsetError)2+ (3σ noise)2))
Correcting for Temperature
Note: For field wiring, the use of shielded twisted pair
wiring is highly recommended.
Measurement resolution: 16 bits (including sign)
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Algorithmic Closed Loop Controller and
Remote Channel Multifunction
To calculate accuracy over temperature range outside the
±1 °C range, results after *CAL are given by replacing each of
the above error terms as follows:
Intrinsic functions:
interrupt( ), writefifo( ),
writecvt( ),writeboth( ),
min( ), max( ), abs( ).
Other functions:
Create own custom
functions to handle
transcendental operations.
(GainError)2 + (GainTempco)2
I/O General
(OffsetError)2 + (OffsetTempco)2
Loop Control Specifications
Number of loops:
1 to 32
Default control
algorithm type:
Maximum VT1415A loop update rate
for default PID algorithm:
(Note: VT1422A maximum sample rate is 25 kSamples/s,
compared to 56 kSa/s for the VT1415A. The loop
speeds of the VT1422A are reduced in same ratio.)
1 loop:
8 loops:
32 loops:
3 kHz
1 kHz
250 Hz
Custom algorithm development:
Variable types:
variables, array local and
global variables.
Subset of C programming
language including ifthen-else, most math and
comparison operations.
Scalar local and global
A total of eight (8) Signal Conditioning Plug-ons (SCPs)
can be installed in most combinations of input or output
configurations on a single VT1415A/VT1422A.
Power Available for SCPs
±24 V:
5 V:
1.0 A
3.5 A
General Specifications
VXI device type:
A16, slave only,
Register based
Shared memory:
VXI buses:
TTL Trigger bus
VXIplug&play with
Source Code
Instrument Drivers - See the VXI Technology Website for driver availability and
Algorithmic Closed Loop Controller,
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Algorithmic Closed Loop Controller and
Remote Channel Multifunction
Ordering Information
Includes Spring Clamp Terminal Block
Algorithmic Closed Loop
Controller, Includes Screw Connector Terminal Block
Interface to rackmount terminal panel
Remote Channel Multi-function Data Acquisition & Control Module
16-Port RJ-45 Connector Block (supports VT1415A also)
Screw Terminal Connector Block (supports VT1415A also)
Spring Clamp Terminal Connector (supports VT1415A also)
8-channel Direct Input SCP
8-channel 7 Hz Low-pass Filter SCP
8-channel Programmable Filter/Gain SCP
8-channel Current Source SCP
8-channel 120 Ω Strain Completion & Excitation SCP
8-channel 350 Ω Strain Completion & Excitation SCP
8-channel x16 Gain & 7 Hz Fixed Filter SCP
8-channel x64 Gain & 7 Hz Fixed Filter SCP
VT1510A4-channel Sample & Hold Input SCP
VT1511A 4-channel Transient Strain SCP
8-channel 25 Hz Fixed Filter SCP
8-channel ÷ 16 Fixed Attenuator & 7 Hz Low-pass Filter SCP
4-wire Resistance Measurement SCP
4-channel High-Speed Bridge SCP
8-channel Voltage Output SCP
8-channel Current Output SCP
16-bit Digital I/O SCP
8-bit Isolated Digital I/O SCP
Enhanced Frequency/Totalize/PWM SCP
Remote Channel Signal Conditioning Plug-on (VT1422A only)
73-0025-002 Option 011 Screw Terminal Connector Block
73-0025-003 Option 013 Spring Clamp Terminal Connector Block
73-0025-004 Option A3F Interface to Rackmount Terminal Panel
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