1989 Volume 2 Issue 5 Pages 161-165
Vibrating amplitude measurment using a condenser sensor has a weak point that measuring sensitivity varies by the distance between the probe and the vibrating body (lift-off).
This paper describes an instrumental technique suitable for industrial-measurement of the vibrating amplitude in the range 1-100, μm.
In order to achieve constant sensitivity against lift-off changes, the two kinds of power sources are supplied in series with the vibrating body and the probe. One is a DC source and the other is an AC (high frequency) source. The resulting composite signal are separated into two signals by a low and a high pass filter. Low frequency component (eOL) is proportional to the vibrating amplitude and inversely proportional to the lift-off squared. High frecancey component (eOH) is inversely proportional to the lift-off. Then lift-off compensation is achieved by performing an operation (eOL/e2OH) on an electronic circuit.
When the efective area of the probe is 4.11mm2, the lift-off compensation covers from 0.2mm to 2.0mm within the error of 5 %.
