Mass flow meter
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We currently have a mass flow meter from Xi’an Dongfeng Electromechanical. The panel indicates that the instantaneous flow rate is stable, but the control room shows significant fluctuations. Upon inspection, it was found that there are also large fluctuations in the current output of the flow meter. What could be the common causes for this situation, according to those with more experience? How should it be handled?
The mass flow meter output circuit board may be faulty.
Parameters such as the damping coefficient can be set in the panel; based on the actual current value, control is exerted to maintain a stable flow rate. At times when the flow is stable, it is necessary to check whether there are any fluctuations in the current, in order to determine whether the issue lies in the manufacturing process or in the flow meter itself
Stable flow rate, stable process, stable panel display, large fluctuations in current output
Disconnect the external circuit, connect the power supply for direct measurement, and separate the instrument from the circuit. Then determine which part has the problem.
First, determine whether the process is stable; if it is stable, then there is interference in the external wiring.
If the process is confirmed to be stable, then the focus should be on the flow meter itself: first, check whether there is electromagnetic interference in the surrounding environment, and whether the instrument is properly grounded； The second possibility is a circuit board failure; you can try replacing the circuit board ； Third is a power supply issue with the instruments; check whether the signal channels of the DCS or PLC are functioning properly, as well as whether the power supply is working correctly
You can rule out the following aspects one by one: damping, drive amplifier, grounding, vibration, and electromagnetic interference, etc.
The process should be fine; check the instrument conversion and wiring issues!
It seems that it’s not certain whether the flow is pulsating or not. 1: First, use a clamp-type ultrasonic device for calibration to check for pulsating flow. 2: Don’t assume there’s a hardware failure right away; if there’s a spare cable, use it to transmit signals via RS-485 to see if pulsation is present. 3: Only then consider issues such as electromagnetic radiation or hardware failures related to the cable installation. By the way, if a mass flow meter is used, accuracy must be taken into account – using an electrical signal for transmission significantly reduces accuracy. Why not use pulse signals to send data to the DCS, thereby minimizing losses in conversion accuracy?