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jonala

Solid state relay to Plc input

7 posts in this topic

How can I make a solid state relay (OPTO-22, G4ODC5) turn off when connected to a plc input? The LED on the relay shows that it is off but the plc input shows that it is on.

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Maybe you have a wrong polarization for the PLC input. Check if it is PNP or NPN, and if it match the Opto22 polarization. Regards!

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I would check leakage current when relay is off. PLCs are very sensitive and can see mA or two as on signal. If this is the case you can add additional load in parallel with the input to 'sink' the leakage current.

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J.Guillén, I'm switching a O vdc signal, there is no polarity. Panic Mode, What size resistor? The OPTO -22 relay has a rated 1 mA of leakage. My backup plan is to go with Continetal Ind. SSR I.O-ODC-RL-060 which has 100 microA leakage. The reason I don't go with a regular relay is the process is running at 10Hz. Thanks for your help.

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To get a current flow into the input you must have a potential difference, even switching a 0v line has a polarity. If the voltage being switched is 24v then a 2k7 0.25W resistor across the input will do.

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Usually better to use a transistor.

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Got it working! The 2.7K resistor and swapping the wires did the trick. Thanks again

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