Capacitive Sensors
The capacitive measurement principle was invented more than 40 years ago and has proved its effectiveness ane reliability in innumerable applications. The capacity of a capacitor is influenced by the distance of its electrodes. This correlation can be used for the distance measurement. The sensor heads measure without contact and with an extremely high resolution the distance to conductive targets. The connected electronics display the measurement result directly on a meter (KS series). All electronics provide an analog output signal, proportional to the measured distance, that can be used for further processing. The capacitive probes provide reliable results even under extreme conditions, like in nuclear radiation, close to 0 K, or in high vacuum applications.
Capacitive Sensor KS
| Ranges | 0.05, 0.2, 0.5, 1, 2, 3, 5, 10 mm |
|---|---|
| Resolution max. | dynamic 0.01 % |
| Linearity max. | ± 0.2 % |
| Analog output | 0 - 10 V |
| Operating temperature | -50...+200 °C |
| Protection class max. | IP68 |
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Capacitive sensors - applications
Capacitive transducers are used in highly dynamic fields. Their high resolution and resistance to temperatures of up to 200 °C predestine capacitive transducers for dynamic measurements in extreme environments.
Capacitive displacement sensors are used for distance measurement in low-temperature as a reference system for other distance sensors. Other typical applications are tolerance testing in mass production, vibration measurement, strain measurement, thickness measurement and thickness control of thin metal foils, thickness measurement of plastic foils during production, bevelling and bending of wafers in semiconductor production and many more.
Measurement brake disc
Brake discs of vehicles are exposed to very high short-term loads. The mechanical abrasion and the extreme temperature development on the brake disc have considerable effect on the microstructure of the brake disc. The material used must be able to withstand these loads for as long as possible without changing its microstructure. Fine cracks lead to a break when the load is reapplied and endanger the vehicle.
Capacitive sensors are used in the measurement of brake disc deformation. Due to the high temperature development, very few sensors are suitable for operating close to the measurement object. Capacitive transducers detect changes in the nanometer range and measure the wear on the brake disc.
Capacitive transducers – dynamic measurement at turbines or engines
In turbines the centrifugal forces exerted on the turbine blades result in the expansion of the blades. For the design and construction of turbine blades it is essential that no imbalances arise that unbalance the system.
Capacitive transducers detect changes in the nanometer range and provide crucial data for the FEM analysis.
Measuring Principle Capacitive Sensors
The design of the WayCon capacitive sensors is based on the fact that the reactance of an ideal plate capacitor is proportional to the distance between the plates. The measurement sensor is a guard ring capacitor, whose guard ring is connected to the inner shield of the double shielded measuring cable. A negative feedback amplifier keeps this protective shield tuned exactly to the potential of the sensor center electrode. This ensures in the entire measuring range an almost homogeneous field between the capacitor plates and nearly complete independence of changes in cable capacity. If an alternating current of constant amplitude and frequency passes through the sensor capacitor, the amplitude of the alternating voltage between the capacitor plates (electrode of sensor and object to be measured) is proportional to the distance between the two. A 20 kHz oscillator of highly constant amplitude and frequency provides the sensor current as well as a compensating voltage which can be selected by means of a precision potentiometer. Through a low - pass filter and an amplifier the voltage difference is conducted towards the output terminal.
As described in the above section of the operation of the distance meter, the measurement is affected by the properties of the dielectric. Generally the sensor will be used for measurements in air. The area between the sensor and the target should be completely free of dust, oil or water. If necessary this can be achieved by blowing some air through the gap between sensor and target.
