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When using the Multi-State Indicator object as a message center for like alarms, I have noticed that if I have more than one message showing up at a time, then i get an error message saying message not programmed. I read the manual and it stated that it displayed one bit at a time so my messages in my routines are at the bit level, for instance, when messageboard[0].1 goes high it, the message shows up in the HMI as an alarm, so I wanted to ask if there is another way to use that message center with alarming?

Rather than bit number, I use message number (General tab, upper right).

This means in my program I have to move a number for each alarm bit I generate, but I found it to be more useful for me than the Bit Number setting, which did not work well for what I wanted. It allowed me to program many messages or alarms in a single number file. Just rather than setting bits in my program for each alarm, I move a number into an integer for each alarm.

From the help file on Multi-State Text Indicators:

Note:The Tag Name must only have one active bit. If the Tag Name value has more than one active bit then the Non-Programmed Message Action (see item j) will display.

So if you want to use Bit Number, you have to only have one bit high at any time. Otherwise you will need to use Message Number and convert your alarm bits into numbered alarms in your program.

For those that don't use bit alarms and instead use numeric values of integers, I have a question for you:

What do you do if 2 or more alarms occur that could have values in the same integer register? Do you have logic to cycle between them? Does your application simply not permit more than one alarm or fault at a time?

bjh said:

For those that don't use bit alarms and instead use numeric values of integers, I have a question for you:

What do you do if 2 or more alarms occur that could have values in the same integer register? Do you have logic to cycle between them? Does your application simply not permit more than one alarm or fault at a time?

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Depends on the machine. Sometimes I cycle them on something like a 2 second timer, if they are important alarms. But usually I just set a priority. If two alarms (or more) occur at once, the most important one is displayed first, once it is cleared, the other is shown. I always set a priority based on which one is the most serious vs which is merely just a warning or even a status of the sequence. The Alarms exist, they just only see the most important one, until it is cleared.

Good thing about moving a number into a single Integer, at least in a SLC500/Micrologix PLC, is the "Last One Wins" rule. So I just set all my alarm moves in the ladder in order of priority. Least to Most. Then if multiple alarms are true, the last one that got scanned is the most important one, and displayed.