PLC program loss

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
An AB 1500 I installed 25 years ago has lost its programming twice in the last month and appears to be associated with a rebar driven into one of the 480 volt Cu feeder conductors. Not a failure but a ground fault. It has been dry since the 1st of September with only two rains. Each program loss coincided with the rain. The rebar caused fault was found during the 2nd rain.

The extremely expensive second PLC battery installed a few years ago has good voltage.

Would a SPD installed on the 1KVA(?) secondary feeding the PLC and associated controls help?
 
ptonsparky said:
Would a SPD installed on the 1KVA(?) secondary feeding the PLC and associated controls help?
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SPDs are for protection against fast rising voltage spikes not surges and definitely not voltage drops, dips, or sags.

A ground fault most likely causes a low voltage condition which is best addressed by a constant voltage source like a UPS.
 
Be aware that adding the UPS will likely require that you power down the PLC, so have a copy of the program (and programming software) handy in case the memory gets lost yet again. Since you're already taking the thing down to add the UPS, I would also add a wrap-around bypass of some kind for when (not if!) the UPS faults. I've used Vertiv's MicroPOD switches a couple of times for this sort of thing, and would think that APC and Tripp-Lite make similar devices. If the UPS you choose uses VRLA batteries (and most small systems will), be sure to mark the in-service date and put those things on a two-year rotation.
 
ModbusMan said:
Be aware that adding the UPS will likely require that you power down the PLC, so have a copy of the program (and programming software) handy in case the memory gets lost yet again. Since you're already taking the thing down to add the UPS, I would also add a wrap-around bypass of some kind for when (not if!) the UPS faults. I've used Vertiv's MicroPOD switches a couple of times for this sort of thing, and would think that APC and Tripp-Lite make similar devices. If the UPS you choose uses VRLA batteries (and most small systems will), be sure to mark the in-service date and put those things on a two-year rotation.
Click to expand...
Excellent advice.
 
ptonsparky said:
I suspect if we do anything I will opt for much simpler PLC. Things have changed in 25 years.
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AB's New Micro 820 might be a good fit for replacement. It uses Allen-Bradley's free Connected Components Workbench Software (CCW) if you are unfamiliar with it. That way, you are not changing vendors. ;)
 
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