I am using a SLC 5/03 processor with the following config:
A13 RACK
1746-P2
1746-IM16-3nos.
1746-OW16-3nos.
1746-NI8-1 no.
1746-NR4-1 no.
1746-NT4-1 no.
1747-KFC15-1 no.
1746-HSCE2-1 no.

The SLC frequently faults while in RUN mode. At first the problem was with the NR4 module showing fault that all channels are open-circuit. I tried changing the slot position, sensors, but was unsuccessful.(2 RTD modules failed). I used PT100 to 4-20 mA converters at last to overcome the problem. Things then went well for 7-8 days.
But now the problem has recurred again with the 1746-NT4 module. The fault message says "Speciality I/O module in slot 9 has created a generic error." The fault resets on recycling of power. The SLC faults frequently; about 5-10 times per day.

I am rather confused as to where the source of the problem might be. I checked the wiring, rewired the SLC and control power cables, fitted in locally available line filters(230VAC). I even changed the 1746-P2 power supply but in vain.

Please detail on what might be the reason for this. Can the problem be with the Processor itself. Please help
I need to fix this urgently!!!

Thanx.
Rahul

 

Check the backpane and the earthing I faced similar problems earlier though not so frequent. Might Help

 

The 24V DC runs close to capacity.

Do you have anything connected to the user 24V DC?
Have you checked your earthing/grounding?
Are there any dips in the supply voltage? (Large drives starting etc)

Vince Dooley

 

Sounds like you have grounding problems. No PLC (regardless of price) should "frequently fail". You'll need to add isolated analog transmitters or use isolated sensors or sensor wells.

regards
- LynnL, www.digi.com

 

Rahul

Get a seperate 24vdc supply to handle all of your loops. Do you have additional items on the loops?
It could be that the analog input module itself is defective. (the NT-4 module?) But for sure make sure you have no ground loops, solid 24vdc power to all transmitters/sensors (a really long run on a loop can cause serious voltage drops), check all ground connections and power connections, make sure your shield on the loop cables is not tied to ground at both ends. If all else fails, get ahold of Allen Bradley, check that all config files and applications are compatible, verify you have the latest software for the processor, check the errors.
Does this happen with the NT-4 module installed or not?
What other symptoms are there?
Are you seeing other errors or module fault codes?

matt
technical consultants
[email protected]

 

Rahul---

Along with the other correspondents, I wonder about your grounding, 24V backplane loading, and the A13 rack itself. Please consider their comments carefully.

I note that your problem is apparently outside of what the SLC500 fault detection system can handle. The original fault was clearly not correctly diagnosed by the system, and the later faults have been generic. The fault detection system knows a lot about your SLC500 system, and if it doesn't work, there must be something about your system that makes it different from a normal system.

One of the characteristics of the SLC500 fault detection system is that it works left to right, and I have seen it accept a compromised module, then fault on a module to the right. This has only happened when there was something terribly wrong with the compromised module, such as being installed outside of the card guides. (This takes great strength and determination!)

I'm suggesting that you remove and replace the NI8 module, then try RUN Mode with the front signals disconnected. If that doesn't fault for a while, reconnect the front signals, and see if that brings back the faults.

The NI8 is the best way that grounding problems can get into your system. I'm recommending that you look at it to find your answer.

Hope this helps!

Larry Lawver
Rexel / Central Florida

 

hi

thanx for the reply.

as regards 24VDC loading, i haven't used the SLC power supply for external loads, i have put in a separate 24VDC power supply.
also i have removed the NR4 & NO4I module which leaves quite enough margin for the power supply.
I can't replace the NI8 module right away since i don't have a spare, but i will try replacing the chassis with one from another PLC. Can problems with thermocouples or the NT4 module cause the NR4 module to fault first?
looking forward for some suggestions from your side.

thanks again
Rahul

 

It appears that there could be some potential leak through into the PLC.
Ground 24 v dc power supply (any one terminal)
Make sure your thermocouple units shell are fully earthed and ther is no chance of voltage leak from the heaters.
If the defective units can work in a different chassis ( when you just test them), the problem could be PLC PSU overloading Change to higher PSU or split into different chassis.
If the fault can be reset looks like PSU or Chassis dirty of chips etc. Did any body drill the panel to install things like switches PB or a fan? Look carefully on the chassis for any debris
regards,
Sekar

 

Some time ago I had a problem which sounds similar to what you describe... SLC5/03, no special module though, over a year of flawless operation, suddenly random processor faults, etc... We discovered that the 120/240 selector switch had been left in the 240v position even though we were using 120v! It seems that it ran ok until the line voltage dropped slightly, just enough to fault the processor! Obviously a power supply related problem so I would pay some close attention to that area.