I'm using a 3 wire inductive proximity sensor to trigger a 24vdc SPDT relay. The relay has a minimum pickup current of 8mA with an unknown dropout current (the mfg. cannot provide a spec for that for some reason). The problem is my sensor has a leakage of 4 mA when off. What's happening is when I initialize my system, the 4 mA is not strong enough to trigger the relay, when the sensor does turn on, the current jumps to 17 mA and the relay picks up; however when the sensor turns off, apparently the 4 mA is enough to prevent the relay from dropping out.
I've looked on line and while there is a lot of information about bleed resistors for 2 wires sensors, there's nothing for 3 wire, so I don't know if a bleed resistor is feasible. If it is, does anyone know if there is a formula for figuring out what the resistance should be? I've also tried a socket with an RC network that didn't fix the problem, and have experimented with different resistances in parallel to the coil and running the the 24vdc return, but either the sensor doesn't trip, or it's the same problem with leakage current keeping the relay on after actuation. Any suggestions would be appreciated.
I've looked on line and while there is a lot of information about bleed resistors for 2 wires sensors, there's nothing for 3 wire, so I don't know if a bleed resistor is feasible. If it is, does anyone know if there is a formula for figuring out what the resistance should be? I've also tried a socket with an RC network that didn't fix the problem, and have experimented with different resistances in parallel to the coil and running the the 24vdc return, but either the sensor doesn't trip, or it's the same problem with leakage current keeping the relay on after actuation. Any suggestions would be appreciated.