It was our goal to develop noise resistant sensors. Basically, a capacitive sensor is a noise detector. Its reacting to electrical fields makes it also sensitive for electrical noise.
In our technology the sensor is a receiver of a certain frequency. Lower frequencies are suppressed quite well. We therefore use a frequency of about 2.5 MHz. This is beyond all frequencies that are used or caused by any drives. Additionally, noise, shorter than the required reaction time, is filtered out digitally. Regarding noise resistance tests with roller mills, coil winders, and collaborative robots were a great success.
An alternative approach is to use double sensors with equal surfaceses. One of these sensors protrudes the other. An approaching obstacle will influence it stronger than the other sensor. By contrast, noise will affect both sensors equally. Processing only the difference of both sensors signals will reveal only the approaching obstacle. The carrier frequency may be much lower then.
The measures mentioned in the chapter Temperature Stability guarantee a working point in a linear sector. In addition to the ESD protection – which is realized easily and effectively – the circuitry will not be blocked by strong pulses.
The sensors proved to be functioning flawlessly under industrial conditions.