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Sanif

RackStatus bit on 1771-ASB

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There is a ControlLogix that was connected to 1771-ASB via Remote I/O. This equipment has been running for a couple of yrs now and lately we have been getting RackStatus bit =1. I checked the manuals and the RackStatus bit 0 means it is good data, 1 means bad data. It doesn't give any more information. In spite of the intermittent RackStaus bit going High, there was no process interuptions, meaning it didn't affect our equipment. Has anyone encounter similar problems and is this a prelude to some module failures? Thank you.

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I deal with AB RIO a lot, but never have used it with controllogix, so this information is general, but probably still applies. There should be a set of counters that are used to monitor the communications. With A PLC5, you can assign a data table to the status of a RIO channel and get information like: Messages Sent, Messages Recieved, Messages Sent with Error, Messages Received with Error, and retry coutners for each rack on the channel. If you can find these counters in your controllogix system, you should be able to determine the location of the problem. My RIO problems are often caused by noise. Sometimes, though, a failing adapter module will intermittently suffer from numerous retries before crapping out completely. I've had several 1794-ASB (Flex I/O) that have intermittent communication problems that vanish when they are replaced. The first thing to look for if you have a lot of counts in the "messages with errors" category is electrical noise. If you get a lot of retries to a particular rack, you may have a poor connection or a problem with the adapter module. I don't use controllogix enough to be able to help you find these counters, but I'm sure that they are buried in there somewhere. Hope this helps, Paul C.

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Check the right Termination (Resistors at both ends of the physical first and last Rack). Important is also the value of the resistor, dependend of the Baudrate(150/82 Ohm). I've seen similar effects, for example after replacing a Panelview on the same RIO we've got randomly Rack Faults at a Block I/O module. We could see that the Retry Counter was counting up frequently. Before replacing the Panelview this machine was running with wrong termination for years without any stop regarding this module.

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If you want to use these counters OkiePC mentioned, you have to program some MSG's in your logic: http://domino.automation.rockwell.com/appl...57?OpenDocument Edited by KlausR

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Oh yeah, I forgot all about termination resistors. When I first got into this field I was responsible for 36 machines with RIO. Not a single one of them had a terminating resistor at any end point. All the DH+ and RIO cables were routed in the same conduits with VFD motor leads, 120VAC control wiring and all sorts of other stuff. It all still worked somehow. I did go back and correctly terminate all the blue hose with the correct resistors after I got involved in one or two occurences of chasing ghosts. When you look at the status counters, you can then see the improvement when the system is properly terminated and the comm cables are properly routed. I've even heard stories of 120vac connected to the DH+ channel of a PLC5 and it still worked! That's a story I'd have to see to believe, but DH+ and RIO are very solid communication systems, and are almost bulletproof even when the rules are broken during installation.

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Thanks for the tips. I went around the plant to check the cables and terminations, all seems to be in order. The electrician had a round the previous shift and had tightened and check all cabling, it seems. However, I found something interesting. The RackStatus bit goes high just before a solenoid valve opens. We will check this out today to see if the RIO is affected by the noise from the solenoid. I'll keep you posted.

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We managed to pin down the culprit. The connection near the solenoid valve was not in perfect condition ( traces of water and dirt..scary isn't it). The solenoid opens a valve that collects dusts. We clean it up and everything is fine so far.

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Sorry..that was me who posted as Guest. I didn't realise that I wasn't logged in.

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