Guard ring capacitor

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Circuit diagram with guard ring capacitor for testing insulation

A guard ring capacitor is a special design of a plate capacitor to reduce edge effects from measurement processes.

construction

A guard ring capacitor consists of two parallel, circular electrodes. In contrast to the normal plate capacitor, however, an electrode is divided into two concentric areas: a circular measuring electrode on the inside and a protective ring on the outside. Both areas are electrically isolated from each other.

functionality

The graphic opposite shows a basic measurement setup for testing insulation materials. The test item is located between the plates of the guard ring capacitor. The ohmic sheet resistance of the test object is determined by measuring voltage and current. The current flowing through the guard ring is not taken into account. This eliminates the inhomogeneous field at the edge of the capacitor during the measurement.

Applications

Guard ring capacitors are mainly used in measurement technology, for example in capacitive displacement sensors , when testing insulating materials (determining dielectric strength ) or voltage scales .