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Micrologix 1500 Error Problem

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I'm having an interesting problem with a Micrologix 1500 installation. At seemingly random times (about 1 or 2/week), I was getting: "Error 22 - The user watchdog scan time has been exceeded". When I cleared the fault from the error screen, I immediately would get: "Error 187 - I/O configuration mismatch, check module 1. The expansion I/O configuration in the user program did not match the actual configuration, or specified a module that was not found, or the data size for the module was greater than what the module is capable of holding". The only way to clear that one was to cycle power. (I had set the auto clear fault and auto run pits on powerup. Usually, the watchdog timer indicates a self inflicted software problem such as an endless loop. However, my code has nothing exotic in it (see attachment). Also, the scan times are about 1/10 of the watchdog timer setting. We swapped out the processor and still had the problem about a week later. Anyway, at the risk of masking the problem (and at A-B's suggestion), I set the watchdog time value at the max value of 255 (x 10 msec). We ran fine for over a week and then got: "Error 71 - The controller cannot communicate with an expansion I/O module. Exact module cannot be determined." A-B tech support is stumped. My personal theory is a heat issue. This gets kind of blown away because I have 4 more similar systems installed that don't have the problem. All are outdoor sites, but the problem one is in the trees and should be one of the cooler sites. I've just put a temperature data logger in the panel to see if we can correlate the crashes with temperature in any way. I've also checked the grounding at the site. Power is 24 VDC battery charger floating batteries, so that should be good. Any ideas? Thanks.

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Have you got a spare rack that you can swap out with it? Over the years, the majority of problems I've had with the SLC 500 modular systems has been traced to the rack. Had a bad 24Vdc output card about 2 weeks ago and that was the first in quite a long time. Its been forever for a processor.

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I recently had I/O problem in a SLC remote rack connected to a PLC5 that was traced down to electrical noise getting to the backplane through a contact output module (1746-OW16). The errors I got were similar. Sometimes the processor (1747-ASB scanner) could not communicate with a specific card, other times it could not identify the card with the problem. I changed it to a solid state (TRIAC) output card and the problem went away. Don't know if your situation is similar, just a thought.

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What are the expension cards , Sometimes this is a noise related problem .

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Check the white bus connection clip on the first card. if it is not hard latched to the left this kind of error message is generated.

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Thanks for the comments. I took a few days off, so I'm late replying to the posts: I don't have a spare rack, but can get one. The local A-B rep has been very helpful in substituting parts - no questions asked. Anyway, at A-B's suggestion, I will try replacing the end cap first. I am still gathering temperature data from the data logger to see if there's any correlation there before swapping hardware. I am using a couple of the on-board relay outputs as dry contacts. They normally do not change state unless there is an alarm. The only expansion modules are 1769-IF4 analog input modules (4 ch.). The other sites have only one analog input module. I had the tech check the white expansion clip and he says it looks good to him. Something else I didn't mention in my original rambling is that this PLC is being polled over a radio. Comm setup: DF1 half duplex slave at 9600 baud. Radio: Freewave #FGR115RC, Spread Spectrum Host: Intellution Fix 32 using RSLinx. It get polled about every 5 seconds. Only sends about 12 words of data.

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A-hah!!! I now have your answer. The problem is with the I/o in the remote rack. There has been a design problem with then IF4 since it's launch some 3 years ago. If you place the IF4 in a remote rack ( not plugged into the processor slots) and you power down the remote rack before the processor rack this fault will always occur.(try it out by powering the processor and remoterack , then remove power to the remote rack only ) This normally occurs when both racks are powered down from different sources, although I have seen it occur when using the same source, as the remote powersupply can powerdown(depending on it's loading) before the processor power supply powersdown . The reason is that the processor is looking for the IF4's cards diagnostic bits which will fail as the remote rack powers down before the processor power supply. This also occurs with Compactlogix remote racks. The only solution is to make sure that all analog cards for Micro1500's are located with the Processor's rack. RA is aware of this problem............... but no fix has come yet.

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David, The IF4's are not in what I consifer a remote rack. They are expansion cards that plug in directly to the base unit that holds the Micrologix processor. Are you thinking of a SLC setup? I haven't used the Micrologix platform before, so I'm a little unfamiliar with the exact terminology. Anyway, don't forget that the original problem was the watchdog fault. I covered that one up by extending the time to the max value. Thanks.

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The IF4 problem I described is when the base i/o cards have reached the maximum number for the base powersupply .( you can have up to 16 cards depending on the load ) Normally after 8 cards you use an expansion rack made up of an expansion cable, P2 powersupply and an endcap. This rack can have up to 8 cards on either side of the power supply.

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I have seen this problem with Heat or Noise Realed problems One thing you could Done is this in Rslogix 500 Software with the Program offline Click on the Card and Advance Configuration , Check the Ignore Configuration Error and download to the Micrologix Again this Solved a Problem i was having it tripped every 4 minutes or So . ( Note: this is a temperory Fix) Good Luck

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I'll try the "ignore" function. You said that this was temporary - what was the final solution?

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I just went though this problem I added MOVs on all my outputs added A line filter still had the same problem , the Problem ended up being the base unit was bad replaced the base unit and the problems went away .

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Sorry sir, i got this problem also. Did you have any solution for this problem?

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Watchdog problems are almost always either power issues [low voltage, short to ground, etc.] or bad processors.

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