nve abt004-00e tmr gear tooth sensor

The NVE ABT004-00E is a dual-channel tunnelling magnetoresistance (TMR) gear-tooth sensor, pitch matched to a target gear module of 0.4 and a target gear pitch of 1.257mm. Eight phase-shifted TMR elements form two Wheatstone bridges sharing a common Vcc and ground, giving phase-shifted sine and cosine outputs as ferrous gear teeth pass the sensor face. Supplied in a 3 x 3mm MSOP8 package marked FT4e.

Gear Module and Target Pitch

The ABT004-00E is matched to a target gear module of 0.4, a gear pitch of 1.257mm and a diametrical pitch of 63.5. Gear module is the gear pitch divided by pi. It is also the reference diameter divided by the number of teeth. Seven pitch-matched parts cover modules from 0.2 to 2, so the sensor is selected against the gear rather than the gear against the sensor.

Sine and Cosine Outputs

Two phase-shifted differential outputs give incremental position and direction. Maximum output is 600mVpp/V typical, 400mVpp/V minimum and 800mVpp/V maximum with the full bridges pitch matched to the gear. The outputs scale ratiometrically with the supply. Output impedance is low enough to drive a standard ADC or microcontroller input directly, with incremental position recovered using an arctangent function and no external signal conditioning. A dual comparator and flip-flop will give digital speed and direction instead, one speed cycle per tooth.

Common-Mode Field Rejection

The eight phase-shifted elements are configured to reject common-mode magnetic fields from external sources, including the placement of the bias magnet itself. Sensor element linearity is 1% maximum and hysteresis is 1% maximum. The linear range of the sensor elements runs from ±10mT to ±30mT, with saturation at ±50mT.

Supply, Temperature and Operating Frequency

Supply voltage runs from 0 to 10V and the operating temperature range is −50°C to +150°C. Device resistance is 5kΩ typical, 1kΩ minimum and 10kΩ maximum, with a temperature coefficient of resistance of −0.08%/°C and a temperature coefficient of output between −0.1 and +0.1%/°C. Sensor operating frequency reaches 350kHz. In ferrous metal detection the speed is limited by the permeability of the target, so gear-tooth sensing is typically limited to around 20,000 teeth per second depending on the size and shape of the gear.

Biasing and Orientation

The ABT004-00E is back-biased with a permanent magnet to sense a ferromagnetic gear, with the magnet fixed on the opposite side of the board from the sensor and a placement pocket milled into the board where that helps manufacture. The sensitive axis is aligned parallel to the rotation of the teeth. Signal amplitude scales approximately linearly with airgap and reaches a maximum with the sensor face at the gear-tooth face. A strong magnet raises the signal amplitude and can also introduce harmonic distortion by partially saturating the sensor elements, so the magnet is part of the specification rather than an afterthought.

Pinout: Pin 5 and pin 8 are connected internally, as are pin 1 and pin 4. Full pin assignments, application circuits and mechanical drawings are in the product datasheet.

Contact our sensor specialists today to discuss the gear module, bias magnet and mounting for your application, or to request a sample against your specification.