Modicon Momentum Issue

[T Gibbs]

I have a customer who has a Momentum PLC in a machine. There is a soft start that runs a large hydraulic pump, and about 15 solenoid valves that control the machine process. Sometimes the PLC will shut down the motor and start it right back. When this happens all the I/O cards will flash red lights, then go right back to working. It's like the PLC faults out, then resets. We have changed out the processor, connection cables, I/O cards, etc. and nothing works. It happens at random times. Anybody had this kind of issue?

 

[starshippe]

set traps

. . can u put in software or hardware monitors or traps to see if the pump is being told to shut down, or doing so on its own?

bill

 

[T Gibbs]

PLC is shutting it down. When it "faults" all outputs go off, then back on.

 

[starshippe]

do u have access to ladder logic?

. . if so, can u put in temporary logic to see what is causing the output coil to deenergize?
. . I have a hot date with the wife, so might be a bit before I can get back.

bill

 

[T Gibbs]

It's de-energizing because all the I/O cards are faulting out, then coming back. It's not a programming issue, it's something like a loose connection.
The output points are good for 2 amps each. I wonder what happens if one gets overloaded, like maybe a solenoid coil starting to go bad? I'm leaning that direction, but these fire off so quickly that it would be hard to isolate which one does it. I'm considering adding interposing relays on the outputs, but I don't have a lot of space in the panel, and that's a lot of time to spend if that's not the issue.

 

[starshippe]

fused outputs etc

. . our outputs are all fused. an overload on one output should not take down the system, it should just blow the fuse.

. . we had one problem with timing, where the air compressor controllers would bail if they did not receive comms from the dcs within a certain amount of time.

. . battery powered strip chart recorders, hardware or software based, can be used to trend supply voltages.

. . if its safe to keep the pump running with the valve positions questionable, u could run that output through a timer that would keep it energized thru short periods.

. . if a power supply is getting hot and tripping for a second, try running a fan on it.

. . the grilled salmon and attendant scotch were delicious.

bill

 

[osmanmom]

the motor start again by itself ?

after CPU plc or IO Card error and intermittent happen.

 

[GeoffC]

I would try putting the cpu on a separate 24v supply
Could be a faulty solenoid pulling the system supply down

 

[GeoffC]

Is there noise suppression diodes fitted across each solenoid

 

[chud]

As geofcc suggested put the cpu on different supply.
It can be a short circuit doing this but something should blow in that case.
I suspect it might me a power supply being overloaded or a tansformer being overloaded when all the loads are on at the same time

 

[gclshortt]

I would use a power conditioner / UPS for the PLC. This will ensure that the voltage level is maintained at all times to the CPU.
GeoffC is correct in advising on the surge suppressing diodes for the solenoids.
http://accautomation.ca/get-rid-of-surges-that-are-destroying-your-plc-outputs/

Regards,
Garry
http://www.accautomation.ca