Brett Lang · Motion
CompactLogix analog, loop powered transmitter. After a storm every channel sits a hair under 4 mA. Replaced one transmitter, same reading. Card, 24 V, or a shared common that got lifted?
Allen-Bradley
1769 analog input — 4–20 reads 3.9 mA after a lightning weekend
Imani Cole · Instrument tech
Measure 24 V under load at the card, then at the transmitter. Storms lift commons. If all channels are 3.9, it's the supply or the analog common, not every transmitter dying together. Don't rescale in the PLC to make 3.9 look like 4.
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