Proximity sensors/ Photo sensors etc

Question

WE need to sence cement concrete (little wet). The application is to On/Off a conveyor belt which conveys this material into a hopper. We need to sence the level so that the hopper does not overflow.

Answer 1

You could use an Omron E3JM photoelectric sensor. You then supply anything from 85 to 240 VAC to it. Then you wire up your control circuit to your contactor or drive through the overload or motor breaker auxiliary contact and then to the proxy. You connect onto the common terminal of the relay output and then either run the normally closed or open terminal connection to the coil of your contactor. Then you test it without material. If the conveyor doesn't run change to the other contact and then when the conveyor runs put your hand in front of the sensor so that you can see that it stops. Then take a hand full of concrete and hold it in front to make sure it works. Then run the product in and check that it stops and then set up the sensitivity. Don't position the proxy too close to the area where it dumps.

You can also put an auto or manual switch with which you can over ride and test the system.  

Answer 2

I would be very concerned using an optical sensor in this kind of environment: Cement dust is inevitable, concrete splashes are likely.

I predict that after a few weeks or even days, the belt stops, period.

I would go for a long-range capacitive proximity sensor, or even a long-arm lever with a micro-switch attached.