Well, today we're "gearing up" to talk about gear-tooth rotation sensors, with Jayne at NVE.
Jayne, tell us about GT Sensors.
Sure. GT Sensors are designed for detection of gear teeth and magnetic encoder wheels
in industrial speed sensing.
As this slide shows, GT Sensors have four GMR sensing resistors,
which are connected as a Wheatstone bridge.
The direction of sensitivity is parallel to the sensor plane.
A biasing magnet provides field, and the flux lines are deflected into
the direction of sensitivity by passing metal gear teeth.
The sensor produces a sinusoidal output with one cycle per tooth.
GT sensors use high-sensitivity, low-hysteresis GMR,
to detect even the smallest gear teeth, and to provide a 50 percent duty cycle output
with wide air gap and temperature tolerances.
How about some application tips for our viewers to sink their "teeth" into?
Several things come to mind:
about 1.5 millimeters between the back of the sensor and the face
of the bias magnet keeps flux lines flexible, and able to follow teeth.
Locating the sensor and magnet on opposite sides of a circuit board
often provides good spacing.
Use a thick circuit board with a milled magnet pocket to precisely position the magnet on
a PCB. Most board manufacturers can do that.
If you don't need zero-speed operation, you can AC-couple the sensor to eliminate
offset from imperfections.
The right magnet is important. Ceramic-8 is cheap and has good field properties.
Alnico-8 is good for high-temperature. We don't recommend rare earth magnets because they
can saturate the sensors.
Thanks, Jayne. Where can I "turn" for more info?
You can click to go to the GT-Sensor section of nve.com for info, or to get an evaluation kit.
Or call me at 800-GMR-7141, extension 2.