Capacitive Thickness Gauges and Displacement Gauges: Frequently Asked Questions

Linearity refers to the maximum error range of the measured value relative to the true value of the distance.

For displacement measurements, linearity is the key to accuracy. For example, when using the VE-1520 sensor, the full scale (FS) is 1500 μm, resulting in an accuracy of ±2.25 μm.

In thickness measurement, the distance between two sensors is measured, and the thickness is calculated; therefore, the maximum error specification is twice that of the linearity specification. However, typically, a master piece is used to calibration the reference thickness during thickness measurement. Since the error changes less when the distance change is small, master piece calibration can suppress measurement errors. By preparing a master piece for each type of workpiece to be inspected, minimizing the thickness difference between the master piece and the workpiece being inspected, and also minimizing changes in the workpiece position during measurement, it is possible to keep the error below the specification.