♪ Turn, turn, turn... ♪
Hi, I'm Jay Brown from NVE Corporation.
Today we're going to take a look at a product demonstrator for NVE's
GT Series gear-tooth sensors.
These sensors use high-sensitivity, low-hysteresis GMR,
for a wide air gap tolerance.
Different versions are available to detect any size gear teeth.
Analog versions provide sinusoidal outputs.
Digital versions have a 50% duty cycle modulated current.
This demonstration has:
* The gear-tooth sensor;
* An inexpensive Ceramic 8 bias magnet mounted
0n the opposite side of a circuit board from the sensor;
* Simple amplifier electronics;
* A micrometer mechanism to vary the air gap;
* A motor-driven gear;
* A meter to show the sensor current; and
* A two-channel oscilloscope to show the sensor outputs.
For this for this demo, we're connected to an external 'scope.
There are three types of GT Sensors: * Single-bridge analog sensors;
* Dual-bridge analog sensors; and
* Digital sensors.
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.
Let's go to the demonstration.
First, we have the ABL004 single-bridge analog sensor.
So I'll turn the motor ON. As the gear spins, you see a sinusoidal output
on the oscilloscope.
The sensor current is shown on this meter. Typical sensor current is just one milliamp
for an ABL004 single-bridge sensor with a 5-volt supply.
This is a typical 1.5 millimeter sensor-to-magnet spacing...
As I increase the air gap, you can see the output amplitude decreases,
but stays a symmetrical sine wave.
The amplifier has a gain of about 20, so the amplitude--even at the large distances--
is several millivolts.
With a large gear like this, the sensors typically
operate over at least a 5 millimeter airgap range.
Now we have an ABL014 dual-bridge analog sensor and two channels on the 'scope.
The sensor is positioned approximately 4 millimeters away from the gear tooth.
The dual-bridge sensor has phase-shifted outputs, providing direction information.
Sensor current is typically 2 milliamps; a maximum of 2.5 milliamps.
Current is shown on the meter here.
The third demonstration is an AKL-Series digital sensor.
With this sensor, you see a 50% duty-cycle digital output.
This provides speed information.
As I change the air gap, the output doesn't change.
And if I turn the gear slowly by hand, you see these sensors
work to zero speed, or DC.
This is a current-modulated 2-wire device:
the current switches between 4 milliamps, and 8 milliamps
to indicate a gear tooth.
So to sum up, we've shown that GT Sensors are a robust way
to detect gear rotation, with a wide air-gap tolerance.
Click, e-mail, or call us for more information.