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Electrician Red Seal · Question

A common cause for an analog input reading of 0 mA from a 4-20 mA pressure transducer, even when there is system pressure, is:

A 4-20 mA signal is a live zero signal, meaning 4 mA indicates zero pressure, and 0 mA indicates a wiring break or transducer malfunction (an open circuit). Inc

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Question: A common cause for an analog input reading of 0 mA from a 4-20 mA pressure transducer, even when there is system pressure, is:

Answer options:

  • The transducer is outputting 20 mA.
  • The transducer is calibrated incorrectly. ✅ An open circuit in the transducer wiring or the transducer itself.
  • The PLC analog input module is saturated.

Correct answer: An open circuit in the transducer wiring or the transducer itself.

Explanation: A 4-20 mA signal is a live zero signal, meaning 4 mA indicates zero pressure, and 0 mA indicates a wiring break or transducer malfunction (an open circuit). Incorrect calibration would lead to an incorrect, but non-zero, reading. A saturated module would likely read the maximum value.

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