I have two different machines that have failed me in the last couple of years. They are Compact Logix based, 1769-L32E CPU. The manual specifically says if the battery is OK and able to retain the program that the BATT LED on the face will be off. Every time we have checked on the PLC the BATT LED is off. If you unplug the battery or it is more than 95% depleted the LED will be red. I have unplugged the battery before and have verified that part to be true. However a few times a year a safety conditon will trip the whole electrical panel, turning off the PLC power. It SEEMS like with a fresh battery it is able to power back up but as the year progresses, if we are pushing a year or so, the next time we loose power we loose the program. We will find the panel powers back up in the RUN mode and all of the HMI displays are showing ???? (as in communicating but address not found) because when I get the laptop out I find there is no program in memory. To sum it up, the battery seems to work for awhile then fails. OK, that part makes sense but the BATT LED is not working correctly leading us to believe that there could be something else wrong? Also, we have resorted to buying a compact flash card and storing the program on the card. It is set to load on memory corruption only. This is also fine but not ideal. If we make any recipe changes then I have to remember to store the program again to the CF card. No big deal but I'm human and can forget - or not even know because I don't make the recipe changes. If the Engineer that logs in and makes recipe changes and he forgets to tell me we could be in trouble in a power failure situation. Say the battery is not going to work, and we power down and it restores an older program off the CF card. We will run and nobody will know we are running the wrong chemical times. It would be better to loose the program and make sure you put a good one in at that point. Of course the last time we lost a program before the CF card was installed, it was on weekend production and I was at home. As you can tell, there a few things I am considering here. Also, is there a way once a month that I can program an automatic backup to the card? Write just the recipe addresses to the card so it doesn't have to go to program mode to do a store or something helpful for my situation? This idea is not perfect or elegant but minimizes the risk of keeping a progam in non-volatile meomory that is not up to date. Any ideas? I'm not sure why these batteries are failing me and I'm not sure what I want to do next to eliminate this problem.
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