AG921-07E Digital Gear-Tooth Sensor Demonstrator

AG921-07E Digital Gear-Tooth Sensor Demonstrator
AG921-07E
Digital Gear-Tooth Sensor
Demonstrator
SN12454
NVE Corporation
(800) 467-7141
[email protected]
www.nve.com
About This Demonstrator
GT SensorsTM are designed for detection of gear teeth and magnetic encoder
wheels in industrial speed sensing.
This demonstrator is based on an AKL-Series GT Sensor, which provides a 50%
duty cycle digital current-modulated output.
The demonstrator also includes a circuit board with an LED and a transistor
driver; a small gear that can be rotated; and a battery to power the circuit.
GT Sensors are based on Giant Mangetoresistance (GMR), providing the
sensitivity to detect small gear teeth and wide air gaps. GT Sensors can operate to
DC, and can therefore detect a wide range of speeds, including very slow speeds.
In addition to AKL-Series digital sensors, NVE offers ABL-Series analog geartooth sensors, which provide sinusoidal outputs. Single- or dual-bridge analog
sensors are available. The dual-bridge versions have two out-of-phase outputs for
determining direction.
Quick Start
Airgap
2.5 mm-pitch
steel gear
AKL002-12E
Sensor
9V
Battery
Ceramic
Magnet LED
Modified
AG917-06
PCB
ON/OFF
Switch
(up is ON)
Quick Start
• Install 9 volt battery.
• Turn the demonstrator ON (switch in the up position).
• Adjust the airgap between the sensor and the gear if necessary.
• Turn the gear slowly and observe the LED tuning ON and OFF.
• Turn the demonstrator OFF when not in use to preserve battery life.
Note:
Style may vary from the above image.
Magnetic Operation
As shown in the diagrams at
right, the direction of sensitivity
is parallel to the plane of the
AKL sensor. A biasing magnet
provides magnetic field.
As the gear turns, the magnetic
flux lines are deflected into the
direction of sensitivity by
passing steel gear teeth.
The sensor produces a digital
output with one cycle per tooth.
Magnet
AKL
Sensor
Sensor
Elements
Sensitivity
Output
OFF
Output
ON
Magnetic Design Considerations
The Right Sensor for the Application
AKL-Series sensors have two sensor elements with various spacings. The
following table shows popular models:
Part Number
AKL001-12
AKL002-12 *
AKL003-12
Element
Spacing
(Microns)
1000
500
300
*Included in the demonstrator
Optimal spacing depends on the geometry of the gear and the sensor system.
As a starting point, the sensor element spacing can be one-fourth of the gear
pitch. In this demonstrator, the gear pitch is approximately 0.1 inch (2.5 mm),
so the 500-micron sensor (AKL002) was selected.
Sensor-to-Magnet Spacing
This demonstrator has the sensor and magnet on opposite sides of a circuit
board, providing approximately 1.5 millimeter spacing between the sensor and
magnet. Spacing in this range typically keeps flux-lines “flexible” and able to
follow gear teeth.
Magnet Selection
Ceramic-8 magnets, like the NVE number 12216 disk magnet used in this
demonstrator, are recommended for most gear-tooth applications because of their
low cost and good field properties. Alnico-8 magnets can be used for hightemperature applications. Rare-earth magnets are not recommended because they
saturate the sensors too easily.
Schematic and Electrical Operation
Demonstrator Circuitry
AKL-Series Gear-Tooth Sensors have
4-to-8 mA two-wire interfaces. This
demonstrator provides a circuit board with an
LED and driver.
When the sensor current is 4 mA, the voltage
across the 100 ohm resistor is 0.4 V, which is
not enough to turn on the transistor. With
8 mA the transistor turns on, illuminating
the LED.
9V
6
2.2K
AKL00212E
5
MMBT
2222A
LED
100
Demonstrator Schematic
Voltage
Regulator
3.3V
Switching
Current
Source
GMR
Bridge
A
EEPROM
Gain
Offset
Detector
A
Current Level
AKL-Series Sensor Block Diagram
AKL Operation
AKL-Series sensors include a GMR bridge consisting of two GMR sensor
elements, a voltage regulator to allow a wide range of supply voltages, a
factory-programmable EEPROM for calibration, and an output current driver.
Circuit Board
AKL002-12E
Sensor
100Ω
NVE #12216
Ceramic Magnet
(reverse side)
LED
2.2KΩ
Drive
Transistor
AG917-06 PCB
(approx. 2 X
actual size)
The circuit board in this demonstrator is designed for an AKL sensor in a
TDFN-8 package. The standard AG917-06 PCB has connections for converting
to a three-wire output by adding a 100 ohm resistor (0805 package) and an NPN
output transistor (SOT-23 package). The demonstrator circuit board has been
modified to add an LED and series resistor to indicate an output.
A board is also available with the sensor rotated 90 degrees (the AG916-06) for
sensitivity parallel to the short axis of the board.
For more information: http://www.nve.com/Downloads/gtsensor_catalog.pdf
Limited Warranty and Liability
Information in this document is believed to be accurate and reliable. However, NVE does not give
any representations or warranties, expressed or implied, as to the accuracy or completeness of such
information and shall have no liability for the consequences of use of such information. In no event
shall NVE be liable for any indirect, incidental, punitive, special or consequential damages (including,
without limitation, lost profits, lost savings, business interruption, costs related to the removal or
replacement of any products or rework charges) whether or not such damages are based on tort
(including negligence), warranty, breach of contract or any other legal theory.
Right to Make Changes
NVE reserves the right to make changes to information published in this document including, without
limitation, specifications and product descriptions at any time and without notice.
Use in Life-Critical or Safety-Critical Applications
Unless NVE and a customer explicitly agree otherwise in writing, NVE products are not designed,
authorized or warranted to be suitable for use in life support, life-critical or safety-critical devices or
equipment. NVE accepts no liability for inclusion or use of NVE products in such applications and
such inclusion or use is at the customer's own risk. Should the customer use NVE products for such
application whether authorized by NVE or not, the customer shall indemnify and hold NVE harmless
against all claims and damages.
Applications
Applications described in this document are illustrative only. NVE makes no representation or warranty
that such applications will be suitable for the specified use without further testing or modification.
Customers are responsible for the design and operation of their applications and products using NVE
products, and NVE accepts no liability for any assistance with applications or customer product design.
It is customer's sole responsibility to determine whether the NVE product is suitable and fit for the
customer's applications and products planned, as well as for the planned application and use of
customer's third party customers. Customers should provide appropriate design and operating
safeguards to minimize the risks associated with their applications and products. NVE does not accept
any liability related to any default, damage, costs or problem which is based on any weakness or
default in the customer's applications or products, or the application or use by customer's third party
customers. The customer is responsible for all necessary testing for the customer's applications and
products using NVE products in order to avoid a default of the applications and the products or of the
application or use by customer's third party customers. NVE accepts no liability in this respect.
An ISO 9001 Certified Company
NVE Corporation
11409 Valley View Road
Eden Prairie, MN 55344-3617
©NVE Corporation
All rights are reserved. Reproduction in whole or in part is prohibited without
the prior written consent of the copyright owner.
Manual No.: SB-000-046
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