Information Related to Inductive Type Proximity

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Rugged, Steel-face Proximity Sensors | Automation World

Inductive Proximity Sensors - Balluff

Inductive proximity sensors - Sick

There's no such thing as non breakable. Every piece of equipment can be damaged given the right (or wrong) circumstances and sufficient determination to do so.

First item on the agenda is to determine how they are being damaged, and then take appropriate steps to eliminate or at least reduce the possibility of this occurring.

If they are being collision damaged, then maybe a flush type shielded sensor coil with remote electronics is the answer, if it is water damage, then consider a submersible type, if the culprit is voltage spikes (very common if located near welding equipment of large motors), then alter the offending circuitry to reduce these fluctuations, or include better filtering in the sense circuitry. Extreme heat can kill them and very cold conditions make them very sensitive to vibration, remote electronics can again ameliorate this problem. Chemical attack is another concern

Once you have fixed the problem, rest assured that some other way will be found to damage them.