The proximity-action capacitive sensor converts a variable of interest in technical production terms (e.g. distance or level) into a signal which can be processed further. The function is based on the alteration in the electrical field around its active zone.
The sensor basically consists of an oscillator, an electrode assembly as the pick-up, a demodulator and an output stage
 

Fig. 1.02

The approach of metals or non-metals into the active zone of the capacitive sensor causes a change in capacitance, which in turn causes the RC oscillator to begin to
vibrate.
This causes the trigger stage downstream of the oscillator to flip, and the switching amplifier to change its output status. The switching function at the output is either an N.O., N.C. or changeover contact, depending on the type of unit involved.
The function of the capacitive sensor can be explained in terms of variation in all parameters of the equation for capacitance:
 

C = ε0 x εr x F x (1/S)

From the formula above it follows that objects which have a sufficiently large relative dielectric coefficient (er) and surface will be detected by the capacitive sensor. Besides the standard (multi-purpose) sensor technology, in which the pick-up is a constituent part of the oscillator circuit, there are also more modern processes designed to meet special application requirements.


Sensors using the patented clock frequency modulation process. Here, the sensor is not part of an oscillator circuit, but is activated by an oscillator’s output. This entails significantly higher levels of interference immunity, above and beyond the product standard, meeting the requirements of the German Basic Standard for Industrial Applications.

 


Sensors using the patented FSA process. Here, the sensor consists of several sensor electrodes, appropriately integrated into an oscillator circuit. This process has been specially developed for detecting the fill levels of aqueous solutions, and scores in terms of special compensation characteristics for coping with different tank walls and media adhesion levels.

 


ESD-proof sensors. In addition, a selection of M30 and Ø30 standard sensors are specially protected against high ESD voltages (electrostatic discharge). This enables them to be used in plastic granule conveyor
systems.
 

 

 

The S I E  SENSORIK company manufactures capacitive sensors in 2 versions:

1. Version SK
Here, only the oscillator or a capacitive pick-up is accommodated in the sensor housing. The evaluation electronics are located in a separate housing. The sensor can be separated from the evaluation electronics.

2. Version SK1
Here, the oscillator and the evaluation electronics are accommodated in a single sensor housing. Electronic circuits and relays can be directly actuated by signal preprocessing inside the device

Typical applications:

  • controlling and monitoring
    machine processes

  • sensor for counting tasks

  • through non-metallic tank walls