Magneto-Electric Rotation Detector

The MP-9810/MP-9830 Magneto-Electric Rotation Detector incorporates a magnetoresistive element, permanent magnet, DC amplifier, and voltage regulator to measure gear rotation speeds from very slow to very fast.

The MP-9810 and MP-9830 have a detection section equipped with magnetoresistive elements at the tip of the sensor. This detection section consists of two magnetoresistive elements, MR1 and MR2, and a magnet. By shaping the signal waveform detected by this detection section, the MP-9810 and MP-9830 obtain a square wave output.

The detection unit consists of two magnetoresistive elements MR1 and MR2 and a magnet, as shown in the figure below. Magnetoresistive elements exhibit resistance values proportional to the magnitude of the applied magnetic field. When a magnetic material (gear) is present in front of the sensor, the strength of the magnetic field changes. Therefore, if the position of the magnetic material is unbalanced with respect to each magnetoresistive element, the resistance values will also be unbalanced. When a constant voltage is applied between terminals ① to ③ as shown in the figure below, and the output voltage of terminal ② is observed, the output signal from terminal ② changes in a way that traces the shape of the gear.

As the gears rotate, the above changes occur in a continuous sequence. (See diagram below)

The signal obtained from the magnetoresistive element is waveform-shaped to produce the final signal. Because the amplitude of the signal obtained from the magnetoresistive element is small (tens of mV), changes in the midpoint voltage due to temperature changes or increases in rotational speed can cause changes in the duty cycle or loss of the square wave output.