Accelerometer Frequently Asked Questions

Question number FAQ-1370

Accelerometer output voltage polarity <It seems the acceleration output is inverted when using a charge amplifier?>

We received the following question from a customer:

Regarding the mounting direction of Accelerometer, if the mounting direction on the sample is reversed relative to the sensing axis (front and back), will the detected phase also shift by 180 degrees? It is directly connected to an FFT analyzer. For example, when measuring vibrations perpendicular to a certain paper surface, the direction is reversed if the adhesive surface of the NP-3210 is fixed to the front side of the paper compared to the back side of the paper. Will the phase of the detected vibration also be reversed by 180 degrees?

The answer to this question is as follows:

The axis of Accelerometer (the cylinder) is the measurement direction. The polarity of the output voltage is such that, for example, if the pickup is mounted on a horizontal sheet of paper from above, tapping the paper with your finger from bottom to top will output a positive voltage, and tapping it from top to bottom will output a negative voltage. Conversely, if the pickup is mounted on a horizontal sheet of paper from bottom to top, tapping the paper with your finger from bottom to top will output a negative voltage.
Since the direction changes from positive to negative, the phase shifts by 180 degrees.

Also, when using an amplifier such as a charge amplifier, some amplifiers reverse the polarity (shift it by 180 degrees). To do this correctly, lightly tap Accelerometer with your fingertip to check the polarity of the voltage output.

■CH-100, CH-1200 Charge Amplifier ■CH-6130, CH-6140 Charge Converter	Inverted output
■For direct input with DS-2000 series, CF-3200J/3400J analyzers, etc. ■ Amplifier for PS-601, PS-1300, SR-2200, and NP-3000 series	Output as is

Last updated: 2007-02-19