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AB 1769-IF8 Analogue Card

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Hi, I sit with a problem on a 1769-IF8 analogue input card. The A-inputs is used display values on FT View SE. I got 4 x 4-20mA signals (Ch0-Ch3) on the card, and want to put more signals on the card for display.As soonas i connect the 4-20mA to the card (Ch4 and Ch5) from Altistart 48 Soft Starters the values of the other signals is running up and down like crazy on Factory Talk View SE. Changed the signal cables but still the same.The new inputs is setup in the same way as the first 4. Anyone came across a problem like this or can give advice?

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These kinds of problems are usually solved by using signal isolators see links below for one brand. There are many others though. http://www.miinet.com/products/sg_signal.shtml http://www.miinet.com/problem_solvers/signal.shtml

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I agree. Usually numbers running up and down mean noise(AC) or other. Are you using shielded cable? May require isolators.

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4-20mA loops are supposed to be isolated. AB cheaply doesn't put optoisolators on their inputs (Acromag, Spectrum, and most others do). That being the case since effectively AB's cards are really single ended, see if you can wire it with the same power supply, or else try wiring the negative (return) sides together to force a common reference.

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