opinions on alarm latching in RSLogix500

I am updating an older RSlogix 500 program and am just wondering whether to leave the alarm latching the way it was done or convert it.

Currently it is programmed to use OTL's and the reset bit triggers a clear on one word reserved for alarms and OTU's for the randomly place alarms.

I normally use OTE's with a seal in contact branched down and the alarm reset bit XIO before the OTE to acknowledge the alarms. I also normally but a timer on my reset bit to keep it alive longer than momentary.

just curious on others opinions, I don't like using OTL/OTU unless necessary, like for retaining state

If the current program is working and has no issues, I would add to the logic the way it is currently written.

I typically do it this way and have an alarm display to scroll the faults in the message display.

the writer of the software may have first written the program the way you are suggesting and discovered that not all the faults/alarms were detected.

latching the bit ensures the bit is on when the rung is scanned.

regards,
james

I don't like using OTL's that much either. But maybe some of the alarms were not being "seen" properly by the logic unless the programmer used OTL's like the previous poster said.

I will leave it as is I just put a comment on the B3 word being cleared so no one tries to use any of the free bits for anything and marked them all as spare alarm bits

I'm always of the opinion, if it works and everyone is used to the way it works, don't ever change it.

labeledas said:

I don't like using OTL/OTU unless necessary...

Click to expand...

I don't understand why so many people say that they "don't like" latch/unlatch outputs. I have to wonder if it is because they simply don't understand how they work, and have therefore created problems for themselves in the past due to misapplying them.

I do understand your concern that a latch is memory retentive, and this should be a concern if using a latch for a real world output. What is the problem with a latched alarm maintaining it's on state through a power outage?

Bit_Bucket_07 said:

I don't understand why so many people say that they "don't like" latch/unlatch outputs. I have to wonder if it is because they simply don't understand how they work, and have therefore created problems for themselves in the past due to misapplying them.

I do understand your concern that a latch is memory retentive, and this should be a concern if using a latch for a real world output. What is the problem with a latched alarm maintaining it's on state through a power outage?

Click to expand...

I'd have to agree that "not understanding" has a lot to do with it. The other big factor seems to be "I've seen programs that were hard to follow because of OTL and OTU". From my point of view, it's similar to "I don't like screwdrivers, I use a hammer instead". It's just a tool, it's not the tool's fault if someone uses it improperly.

I would also agree that in this case, I don't think a power cycle should be an effective way to clear alarms.

Same here. I've never understood the aversion either.

I cut my teeth on GE Series 6's, and their latch/unlatch coils were combined in the same instruction. No spreading the latch and unlatch coils out, and obviously, no forgetting to complete the set.

We didn't have any problems...