Acceleration Pickup Frequently Asked Questions

Question number FAQ-1370

The polarity of the output voltage from the acceleration pickup seems to be inverted when using a charge amplifier.

We received the following question from a customer:

Regarding the installation direction of the acceleration pickup, if it is reversed front to back relative to the sensing axis when mounted on a sample, will the detected phase also shift by 180 degrees? It is directly connected to an FFT analyzer. For example, when measuring vertical vibrations on a paper surface, if the adhesive side of the NP-3210 is fixed to the front side of the paper versus the back side, the orientation is reversed; does this also result in a 180-degree phase inversion of the detected vibrations?

The answer to this question is as follows;

The axial direction of the acceleration pickup (cylinder) will be the measurement direction. The polarity of the output voltage will output a + voltage when the pickup is mounted from above on a horizontal plane and the plane is tapped from below to above with a finger, and a - voltage when tapped from above to below. Conversely, if the pickup is mounted from below to above on the horizontal plane, tapping the plane from below to above with a finger will output a - voltage.
Since it changes from the + direction to the - direction, it will be expressed as a phase shift of 180 degrees.

Also, some amplifiers, such as charge amplifiers, invert the polarity (shift it by 180 degrees) on the amplifier side. To check correctly, lightly tap the accelerometer pickup with your fingertip and confirm the polarity of the voltage output.

■CH-100, CH-1200 charge amplifiers ■CH-6130, CH-6140 charge converters	reverse output
■ For direct input such as DS-2000 series, CF-3200J/3400J analyzers ■ Amplifiers for PS-601, PS-1300, SR-2200, NP-3000 series	output as is

Last updated: 2007-02-19