Troubleshooting Relay Output Nuisance On

[FraserJim]

Troubleshooting a Eaton Easy719-AC-RCX. Have three digital inputs and one relay output. PLC input power 120VAC. Each digital input has a 120VAC source thru a NO dry contact. Same source as PLC power. Relay output also 120VAC. Getting nuisance relay output closures when none of the three input contacts close. When measuring with DMM, am measuring 72VAC between 120VAC source and PLC inputs. This is with the input contacts open. Also, when measuring, with DMM on continuity, it shows NO, but triggers the input. Easy719 manual says ON signal 79V. Do I have a problem with the PLC I/O, wiring, or other? Thanks

 

[Saffa]

You can't do continuity tests with the circuit powered...

What is the program in the PLC meant to be doing? Sounds to me like having a look at that first would be the thing to do. Might need a debounce timer on an input or something like that.

When you say you're measuring 72V from input to source, is that been the input and phase? You should measure input to neutral.

 

[chavak]

Welcome to the forum.

Never used an Eaton before, so can't say anything specific about it.

Maybe you should post the schematic and logic here.

For the output to turn ON, is dependent on the logic input to your unit, may not always be based on an input ON condition only, can be based on input OFF condition + some other conditions which have to be verified with the logic within.

 

[Corsair]

Sounds like it could be an electrical noise or a leakage problem on the inputs to me.

If it is noise - the first choice is to eliminate it, possibly by rerouting cables.

A backup possibility is to hang 10K 10 watt resistors across the inputs and see what happens with the stray voltage. (I know the wattage is overstated). You're too close to the input voltage threshold and those thresholds are not that precise because they are a component variation thing.

My take on things is that we'll see more of this since the manufacturer's have such a sick obsession over making things small but nobody has figured out how to shrink a watt (or voltmeter leads or electricians fingers). Input module currents are less which is not necessarily a good thing. It translates to noise problems and maybe contact whetting problems. I like higher input module currents (but maybe I'm senile since I also like 30 millimeter pilot devices). And I lose sleep wondering about high-frequency noise on 'capacitively coupled' input modules.

A related slightly off topic general statement - when dealing with electrical problems isolation beats suppression. Always try isolation first. For example, if lightening is blowing up components on communications lines fiber optics should be preferred over transient suppression. Communications ports in industrial equipment should always be isolated. Don't try to save too much money by combining DC power supplies, etc, etc, etc.

 

[FraserJim]

The system integrator will not release the program or schematics to us. The PLC is in a secured facility, so we cannot bring a laptop in to download the program. It is also a painful process to replace the PLC. I have supplied our client with similar systems using relays, so I have an idea how the program should work.

So I am trying to troubleshoot with the limitations. I did check input to neutral, 2-3 volts. Still wondering where the 72VAC source to input is coming from and how we triggered the input on continuity.

Thanks

 

[FraserJim]

Good call on the noise and resistor. The room is being supplied by a 160kVA UPS. No Surge Suppressor on the load side of UPS. We always recommend industrial grade Surge Suppressor on the output of large UPSs to address internally generated noise.

It is about 5 wiring feet between dry contacts and inputs. All in grounded metal conduit.

 

[dvcochran]

Troubleshooting a Eaton Easy719-AC-RCX. Have three digital inputs and one relay output. PLC input power 120VAC. Each digital input has a 120VAC source thru a NO dry contact. Same source as PLC power. Relay output also 120VAC. Getting nuisance relay output closures when none of the three input contacts close. When measuring with DMM, am measuring 72VAC between 120VAC source and PLC inputs. This is with the input contacts open. Also, when measuring, with DMM on continuity, it shows NO, but triggers the input. Easy719 manual says ON signal 79V. Do I have a problem with the PLC I/O, wiring, or other? Thanks

This sounds like a wiring/electrical problem, not a programmer/programming problem.
Starting at the source, I assume there is a step down to 120VAC, check voltages and grounding AND neutral bond. Then check immediately after step down. Then check at PLC panel. They sound all be exactly the same +/- <1 or 2%
I suspect you have a bonding issue and the voltage is 'floating' around. Check load to ground, load to neutral, and neutral to ground to look for bleed or bonding.
I have seen some weird things happen when a building is not bonded well, creating a situation where it is hard to get a true ground out in the middle of a building.
I also wonder about a back feed from the end effector on the output. Even though you say it is a relay output something could be wired up wrong.

In short, there should be little to no potential on the load side of anything.