Machine faults - first in first out

[chavak]

Hi Everybody,

Need help on this subject. I want to have machine error messages generated in the PLC to display in the Panelview 'first in first out'.
Panelview will only be displaying one message at a time, when the operator resets the particular fault, next one pops up and so on. I an using SLC5/04 with Panelview 1000. There are altogether 38 error messages the PLC is monitoring for. Somebody told me to try FFL commandbut I never used it,,(he doesn't used it either). Altough I tried to explore on it, doesn't work well. If anyone can give me some clues or even sample ladder will be greatly appreciated.

ThankYou in advance

 

[ganutenator]

(disclaimer)While there are more ways than I can count to skin the alarm cat, here are my two cents.

It sounds to me that First in First out may not be what your after. If I understand you correctly, you want to display an alarm only one at a time (based off of priority?).

It has been awhile since I have done a panel view, don't even have the software on my laptop, so bare with me.

One nice little feature with the panelview is the least significant bit feature. This allows you to create a message display object that displays different messages (in your case, alarms) based off what bit is set. If more than one bit is set, the message for the bit which is less significant (more towards bit 0)is displayed. As soon as that bit is cleared, the next one is displayed, and so on.

To prioritize your alarms, you place higher priorty alarms at the beginning of your bit array.

I used this in a past application along side the print only object (works just like the message display object except sends message out printer port). We used an ASCII overhead sign. The highest priority alarm would be displayed overhead, with instructions on what to do to correct the problem. Once they cleared the alarm, the next one would display, etc.

 

[Terry Woods]

I've always felt that, respect to "streaming alarms", that is, one alarm causing another and another, etc., the original causational alarm should be the one posted. That is, "first in, last out".

The point being, if a series of alarms occur, the operator should see the one that caused the avalanche of alarms. All of the subsequent alarms are "by-the-way", or, after-the-fact.

 

[Billando]

Having been both the operator and the maintainer of different pieces of machinery. Absolutely agreee with Terrys reply on this.

 

[john paley]

I think the easiest way to display only the first alarm is to let the PLC handle it. If there is any alarm latched in the PLC, allow no more to latch. Or only allow one alarm at a time to be active. If you reset the first, and the conditions are right for the second, then let the second latch, and so on. I always set mine up this way and group the alarm bits into words. That way just compare the word not equal to zero to check for, and prevent activation of, other alarms. Also, I use latched bits for alarms. Then the alarm reset simply clears, or zeroes, the alarm word(s).

 

[ganutenator]

I agree with the "one alarm theory" you guys are talking about.

Normally done on a "per equipment" basis, and only done for "shutdown alarms"(alarms that will cause that particular piece of equipment to shutdown and has the possiblitily to cause other nuissance alarms).

The original post asked about using a FIFO for displaying one alarm at a time, I tried to provide an easier option.

I may have missed his intent, however, and if he is talking about only displaying the shutdown alarm, then defin. I agree that it should be done in the PLC. Usually I have seen this done by having a coil inhibiting the setting of all new alarms for a group if any alarm in that group is on.

You can still use the least sig bit way to display only one alarm at a time, while still using this "the shutdown alarm that actually caused the machine to shutdown" logic.

 

[Steve_D]

Another Option

A simple way to priorities your alarms is to set your alarm number in a common register. You then have your alarm bits write the corresponding number (or text) to that register in reverse priority, that is your most important alarms are at the end of the logic section. The last numbber written into the register in each scan will be the one displayed, this will not give you a FIFO register but, if ordered correctly, will give you the most important info.

 

[SteveG]

We use the same alarm philosphy as John and Terry with our burner management systems. NFPA calls them First Outs. Basically every possible shutdown condition has a flip-flop. The flipflops are armed with an AND. The ANDs have two inputs, the first is 'No Shutdown Condition Present' and the second input is the alarm condition. When an alrm occurs, the first alrm condition is latched, which in turn blocks out all subsequent alarms at the ANDS. When the shutdown condition is reset, all of the flipflops are reset with the same signal.

This strategy will only give a single alarm as the 'first out' or 'cause of trip'. Any other shutdown conditions that come in after the first out are displayed on a Start Permissive screen.