How much capacity should a capacitor have to take a countermeasure against noise?

When you connect the MP series Electromagnetic Rotation Detector to a tachometer, an F/V converter or other such device, the display value may be unstable or a malfunction (an incorrect reading ) may occur due to the noise in the signal. In this case, when a capacitor is attached to the receiving terminal of the input signal, it serves as a low pass filter and is thus effective in decreasing high frequency noise.

 

As can be seen in the figure below, malfunctions due to signal noise occur most frequently when the noise is near 0V. The MP series Electromagnetic Rotation Detector would be affected by noise, especially at the time of low rotation because of the small signal amplitude.

 

 

The voltage sensitivity of AC signal of the TM series Digital Tachometer and the F/V converter is 0.2 Vrms (= 0.56 Vp-p). It is necessary to select the capacitor that has sufficient capacity, considering the balance of the signal amplitude at the detectable frequency range and the sensitivity of the device.

 

The signal amplitude of the MP series Electromagnetic Rotation Detector depends on the rotating speed and the gap between the detector and the detection gear. Moreover, the stray capacitance from the signal cable and the circuit of the receiver affect the amplitude characteristic. You need to select the capacitor watching the signal by using an oscilloscope, etc.

Revised:2009.05.25



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