Capacitive detectors
A capacitive detector is a technical device. It is used to monitor changes in the position or location of an object.
Working method
The capacitive detector continuously checks the electrical capacity of an electrostatic field . If the structure of the field is changed by moving or touching an object within this field, the capacity changes. This change is measured and can trigger a response.
example
A steel safe should be secured against theft. A capacitive detector can be used to trigger an alarm when the safe is removed.
For this purpose, the steel safe is placed over a steel plate. There is an electrically non-conductive object (e.g. PVC insulators ) between the steel plate and the steel safe . When the monitoring system is switched on, an electronic control unit generates an electrostatic field between the safe and the steel plate.
Constant electrical energy is used to maintain the electrostatic field. The amount of energy used is stored; the control unit remembers how much electricity is used for this.
If the safe is touched or moved, the energy balance of the field changes significantly within a short time due to external influences. If the safe is removed, the field is almost completely destroyed. Opening the vault door also affects the field. This change in the electrostatic field triggers an alarm.
Disadvantages of the capacitive detector
The electrostatic field established for monitoring is influenced by other fields. Mobile communications, computers or other electromagnetically incompatible devices can intensify or weaken the field used by the capacitive detector during operation and thus trigger a false alarm. This is why capacitive detectors are generally no longer reinstalled today.