Light curtains/safety PLC question

[jcraft]

This is probably a basic question but need some info. We have several pairs of light curtains that the OSSD outputs go into the safety PLC and then the PLC sends the reset command to the L/C's. The curtians are reste hundreds of times a day and very intermittently we are getting a #1 output error on some of the curtains. The L/C manufacturer advised that the L/C needs to see a voltage level no higher than 1.3 volts above ground when the outputs are off or we could see the output error. They believe there is an issue with the grounding for the L/C's and advised to check and measure the quality of the ground. The curtains and the safety plc are fed from a separate 24vdc power supply by themselves. Not sure at this point how to measure the voltage on the ground wire. Can you advise the best way to go about this. Thx

 

[jmsmoreira]

You're saying 24Vcd separate power supplies, but with a common 0V, right?

 

[Geoff White]

There shouldn't be voltage drop on the ground. Thats why its called the ground.

Either make sure that all the grounds (0V) of the devices are all connected together or you will need to put interposing relays between them to isolate the signals from each other.

 

[Jeev]

Also check the cable runs, because you may have induced voltage in the cabling.

 

[Logix_Stef]

Also, check whether the common (ground, 0V) of either one
power supply is connected to earth, also check whether the PLC inputs/outputs have some link to earth. Then you may get a floating voltage between one of the ground(s) to earth.

BR

Stef.