Measuring thickness through capacitance

As well as standard distance measurement, thickness measurement is one of the most common tasks of displacement sensors. Normally, two sensors operate differentially, and the thickness of a measured object can then be calculated. The capaNCDT 6500 multi-channel system offers this feature as standard - even in the series production version. Thickness measurement can be programmed directly using the integrated calculation functions, so that subsequently, no PC is necessary for calculations.

Capacitive sensors are always used for thickness measurement when the object is, for example, highly reflecting or when speckles occur with optical sensors. By averaging over the surface of the sensor, measurements can also be made very easily against rough, uneven surfaces. The object being measured must be a metallic conductor or semiconductor. Thickness measurement to 4 decimal places can be achieved using the capaNCDT 6500, as up to 8 channels can be assigned to the controller. Capacitive thickness measurement can be used when inspecting solar wafers, for example.

The system is also used for gap measurement. The application functions in reverse for thickness measurement. In this case, two sensors are guided "back to back" into the gap. The addition of the two signals with the underlying offset gives the width of the gap. For thickness and gap, special designs have been developed to optimise measurements.