Detecting Tiny Gear Teeth

♪ Turn, turn, turn ♪ [Heartbeat] ♪ First gear–it’s all right ♪ Today we’re looking at detecting
tiny gear teeth using NVE’s unique “GT”
GMR gear-tooth sensor. We’re using an ABL006 Gear-Tooth sensor, biased by an inexpensive ferrite magnet. A high-speed motor spins
a fine-tooth gear, and we can vary the speed. A digital meter displays the speed
measured by the sensor; and a microcontroller controls it all. The sensor provides accurate speed measurement from DC to 10000 RPM. The gear has 56 teeth, so at 10000 RPM,
there are nearly 10000 teeth per second. This demands a high-speed sensor. It also demands a sensitive sensor, since the gear has tiny teeth– the gear module is about a quarter-millimeter; the pitch is less than a millimeter; and the depth barely half a millimeter. Here’s how the sensor works: As the gear turns, the magnetic flux lines
from the bias magnet are deflected into the direction of sensitivity
by passing steel gear teeth. The sensor output
frequency is one cycle per tooth. ABL-Series gear-tooth sensors have
various element spacings. The optimum is around
one-fourth the gear pitch, with a fair bit of latitude. The demo uses a 0.3 millimeter sensor
for a 0.8 millimeter gear pitch. Here’s the demo circuit. A low-cost comparator provides
rotation pulses to the microcontroller, and the microcontroller can
easily measure rotation period and calculate RPM. So we’ve seen how NVE GT Sensors
can be used to sense very small gear teeth at very high speed. These unique sensors have: dual-bridge versions for speed and direction; have wide power supply and
temperature ranges; and are avalable in MSOPs or TDFNs. Click, e-mail, or call us for more information, or to order parts or evaluation kits.

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