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I am getting 28 mA from a valve positioner instead of the normal 4-20 mA position feed back!?
The loop contains an analog input module (A-B Flex IE8 module), an isolator (24VDC powered) and a valve positioner. The valve positoner output is ok (4mA for close position & 20 mA for open position) when checked through a mA simulator. But when the positioner output is connected to the PLC input through the isolator, the mA is around 28. The distance between the positioner in the field & the PLC panel is less than 200 meters. Can somebody throw some light on the causes?
The loop contains an analog input module (A-B Flex IE8 module), an isolator (24VDC powered) and a valve positioner. The valve positoner output is ok (4mA for close position & 20 mA for open position) when checked through a mA simulator. But when the positioner output is connected to the PLC input through the isolator, the mA is around 28. The distance between the positioner in the field & the PLC panel is less than 200 meters. Can somebody throw some light on the causes?