Random alarms

We have 6 unit programs with logix 5000, lots of remote I/O. Ver. 20.
Any thoughts on a ton of random/nuisance alarms that keep coming in. They don't shut anything down, just alarms, but are not true alarms. Examples such as module power faults, channel faults, etc. As mentioned, these are not anything that hurt, they are highly annoying and can fill up an FT alarm page pretty quickly. This is on all units, I know the obvious would be wiring or a comms problem, maybe something to do with the scan rate? The usual suspect is 'noise', but if this is the case, pinpointing it? This was a replacement of an old GE system (all of them), so field wiring is intact as it was. It did not exist before this cutover, so I am leaning towards comms. But I am not sure why this would be either. Any suggestions? As a note, these alarms come in even when the units are not running, so it kind of rules out running noise to me.

Your guessing at comms, wiring, scan rate and noise, all in one post.

Have a look at the faults recorded in the controller and tell us what they are. Same for the Remote IO.

If they are in the FT Alarms, then they are user created, or do you mean the Diagnostics ?

janner_10 said:

Your guessing at comms, wiring, scan rate and noise, all in one post.

Have a look at the faults recorded in the controller and tell us what they are. Same for the Remote IO.

If they are in the FT Alarms, then they are user created, or do you mean the Diagnostics ?

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Yes, you are correct. My experience has shown that any of those could be the issue. Was trying to cover all bases I have investigated or was considering. Sorry if I wasn't clear.

These are random module loss of power faults, module channel faults, all random. Could come from any unit at any time. Many of the faults are latching from the module. Many of them can just be cleared with the reset.

These are set up as ALMD blocks and displayed on the HMI.

If I run the system on a simulator, I get none of these, of course I can only have one running and not on their network.

Sounds like a com stack issue to me... Delayed signals, probably caused by excessive retries, causing timing or collision problems...

That said apart from checking and hardening the network I don't have kit specific knowledge that is going to be useful but if you have to option to slow down the scan rate and or bit rate, I would be inclined to give it a try.
if it helps its probably a cabling issue.
Al

>module power faults, channel faults, etc

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You simply have to choose a few and start troubleshooting.

"Comms" or "scan rate" would not cause most of the faults you describe. A failure and reconnection of a network wouldn't cause an I/O module to set a channel over-limit, under-limit, or broken-wire detection fault.

Put a meter or scope on the unit's 24V DC power. Even a multimeter with a "Min Capture" feature will help you figure out if the power is dropping to a point where it might trigger an under-voltage condition on one of the modules, or a reboot of a network adapter.

How are you getting this data into the HMI system ? Are you reading from each skid/unit directly, or is there a data concentrator in the middle, like a "main PLC" or a DCS controller ?

Ken Roach said:

You simply have to choose a few and start troubleshooting.

"Comms" or "scan rate" would not cause most of the faults you describe. A failure and reconnection of a network wouldn't cause an I/O module to set a channel over-limit, under-limit, or broken-wire detection fault.

Put a meter or scope on the unit's 24V DC power. Even a multimeter with a "Min Capture" feature will help you figure out if the power is dropping to a point where it might trigger an under-voltage condition on one of the modules, or a reboot of a network adapter.

How are you getting this data into the HMI system ? Are you reading from each skid/unit directly, or is there a data concentrator in the middle, like a "main PLC" or a DCS controller ?

Click to expand...

Thanks for your reply. Those were my 'original' thoughts, that maybe we had a power issue. Actually replaced a couple of the power supplies..(there are lots of them, each unit has at least 6, I had the guys go through and check for loose connections, tug test, all terminals are tight, as well as the terminal strips. The thing that gets me is there is nothing 'common' about them as far as wiring, they come randomly from any of the 6 units just sitting there not even running. This is where I started with the thinking maybe comms or scan rate, as I am thinking it has to be something 'common' to all units. My focus went to the analog modules, as the maybe the module scan and the PLC scan were off. And the 'speed' of them, meaning that many are basically gone when you go look at the alarm block other than the latching bits. This again led me to scan rate, as I started thinking that if the scan was too fast or had network issues, it would make sense that it may 'see' an open for instance on a channel because it for lack of a better term 'missed' it or something. I was also considering network problems, there is a main server this is what I/you are terming main PLC or DCS) as the network for these units is multi layered. There is modbus involved in the network also, but not for these alarms. These alarms are coming over ethernet to fiber via local switches. Another thing that 'bothers' me is each unit has a local HMI, while the main control room has network connected. FT SE. Even the local HMI's get these alarms (which are coming from their local program). Hope this is not too convoluted a message.