Circuit verification
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I would like to ask the experts here: During today’s circuit verification, a problem was identified. The flow meter sends a signal of 4 milliamps to the DCS, but the value shown on the DCS gauge is not zero; instead, it’s around 10/100. For example, if the full scale inside the gauge is 100, the value displayed is around 10. Why is this? The system in use is a Siemens system. Thank you!
First, measure to confirm that the flow meter output is indeed 4 mA, then check whether the system’s configuration range is set to 0–100; if that doesn’t work, try changing the system channel for testing.
First, determine how many signals are received at the DCS cabinet’s wiring end in order to rule out any interference in the circuit
Refer to the parameter settings in DCS
With the Siemens system, this is probably caused by different range settings for the upper-level and lower-level units.
1. Verify whether the setting on the DCS side is such that 4-20mA corresponds to 0-100%. 2. Check whether a safety barrier or power supply module is installed on the DCS side; also ensure that the signal sent to the DCS is passive – using an active signal will not work.