AC Prox into smart relay

I am trying to interface a 2 wire turck prox into a schneider smart relay. I have a schneider SR2A201FU and a turck BI2G12AZ33XB3131.

When I connect the prox correctly to the input, the input stays on all the time. The prox does function properly, as I have connected it to a relay and it switches as it should. I have used the search and found other people with similar issues. The replies have been basically to connect a resistor in parallel with the input load and it should take care of the problem. This apparently reduces the voltage at off state.

I have tried this with both a 100K and a 220K 2W resistors. Neither configuration gave any change.My controller is guaranteed off below 40 VAC and on above 79 VAC. I have other specs if they are needed. Can someone help me spec a resistor that will help, or tell me what I am doing wrong? Thank you in advance.

Dustin

on your turck prox do you have a red/black wire going to 120v and the red/white going to your schneider input?

The replies have been basically to connect a resistor in parallel with the input load and it should take care of the problem. This apparently reduces the voltage at off state.

Click to expand...

Dustin,

Your description of the Pull-Down Shunt Resistor Fix could mean that you are connecting the resistor in parallel with the prox switch (the input load). I think the resistor needs to be in parallel with the Smart Relay input terminals, so the the "off-state" leakage current through the Smart Relay input is reduced (shunted) to cause the input to turn off.

See this previous picture posted by Milldrone.

The prox switch has a minimum load current of 5mA. Your 100K is a factor of 10 times too high. About 10K ought to do it.

I don't know what the input current on the relay is.

40VAC / .005A = 8KOhm

You must be below this value to get less than 40 VAC at the input.

Since I don't know the relay input current at 40vac, I'm not taking any credit for it. Whatever it is, it would tend to raise the allowable resistance.

But if you use a 5KOhm resistor, you can be certain it will work. Maximum voltage = .005A * 5KOhm = 25VAC. Power = .005A * .005A * 5KOhm = .125W which isn't much power to worry about.

I see where you got your answer mellis; you screwed up, you trusted my numbers.

I didn't give the whole story. If I recall the spec it's 5mA minimum (load current) in the ON state and 1.7mA maximum (leakage current) in the OFF state.

I think either of our answers would actually work.

So, if we go with my 10K we should never see higher than 17V when off. I was a little concerned with the wattage of the resistor if I went much lower. 10K 2W should be okay. I think if he went with 5K, he would need to bump that up to a 5W.

Anyway, anything greater than 24K and the switch doesn't have enough current to operate properly. Which is what I think the OP's problem was.

But if you use a 5 KOhm resistor, you can be certain it will work.

Click to expand...

Except if you "connect a resistor in parallel with the input load". Then whether or not it works depends on the internal off-resistance of the prox switch, which could be 100 kOhms. If it is, then you have not changed anything.

On the other hand, if you connect a resistor between COM and the Smart Relay input terminal, then the 5 kOhm should work.

Yes, you need to size your resistor wattage, for when the output is on, and you have a full 120V applied to it. At 5K ohm, 2.4W a 5W resistor will still get plenty warm.

Thank you all for the help. I am connecting the resistor in parallel with the load (between common and the input terminal). I had actually used the referenced picture to verify already. I will pick up a couple more resistors on Monday and see if it helps anything.

Thanks
Dustin