Store Fault Msgs in PLC vs HMI

Hi all,
In AB Logix V32, SINTs are 1 byte each. If a fault message is 100 bytes long and I have 1500 messages, that's only 0.15MB. Contrary to what I'm hearing at work, I don't see any reason not to write and store the fault, warning and info messages in the PLC.

Is there something I'm missing? At work, they say that it would be common to have so many strings that one would have to order a larger processor. I would argue that even in that rare case, it would only be a matter of 1 additional MB; a small sacrifice.

What do you guys do? Do you only store them in the HMI? It seems less clean/programmer friendly to only store them in the HMI.

I've been making the effort to keep all of the messages in strings in the PLC. Makes it much easier to make changes all in the PLC and not having to also change the HMI as well.

I do 99% of my alarm strings in the PLC

Does AB have an alarming instruction, or do you typically just have a tag in the HMI that reads your string directly?


I mostly work on Siemens stuff, and I'm always trying to make sense of the code I see coming from the other side of the fence.

AB has both the alarm instructions, tag based alarms, and. HMI based tag monitor alarm

When you say Fault messages do you mean you want to log the faults or are you just looking to supply information about the alarm to future programmers.
If it’s just for the programmer information then the tag name and description should supply enough information for the programmer to understand. Frankly if a programmer can’t understand the faults from that then maybe they should not be massing around in there in the first place.
If you want to log the faults then you should do that in the HMI or better yet to a file in a pc
While you could write the fault message to an SD card (provide the plc supports it). If you just log them in the memory, then when the plc is rebooted all the fault messages are lost so they don’t do you much good.
A better way would be to write them to a file on the hard drive of a pc. That way they wouldn’t be lost on a power loss or reboot and they would be available to export if needed.

Thanks for all your inputs.

To GaryS, I wasn't referring to long term logging. We just display all active alarm messages, warning messages and info messages on the HMI for the operator. We also display a small amount of alarm message history, maybe the most recent 50 or 100.