One PT display shows zero while there is no pressure. But the controller shows 12.5% of the range and the mA reading is also 6 mA. When connected to HART, it doesn’t establish communication with HART. when the pressure is increased to at least 12% of the range, the communication establishes. When the pressure is lower than that, it loses the communication again. What could be the possible cause and what could be done to solve?
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Likely the transmitter’s lower range limit or zero point is incorrectly set so that at actual zero pressure the instrument outputs ~6 mA (12.5 %). As a result, the transmitter doesn’t have enough signal headroom to enable HART communications below that threshold. Correcting the calibration/span (i.e., setting the proper 4 mA/0 % point) should fix both the zero error and the communication issue.
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