When it is below 20mA, an additional 0.08mA signal is present at the station control level
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This post was last edited by hkhl on 2020-1-3 23:36. There is a vortex flow meter, with 4–20mA corresponding to 0–100 t/h. When the process is stopped, the flow meter shows a flow rate of 0, but the station control system indicates 0.5 t/h; at this time, the current measured at the flow meter is 3.98 mA. Analog signals were sent for testing, with the following results: when 4mA was sent, the station control displayed 0.5 t/h, which is 0.5 t/h too high. When 12mA was sent, the station control showed 50.5 t/h, again 0.5 t/h too high. When 18mA was sent, it displayed 88 t/h, still 0.5 t/h too high. When 20mA was sent, the reading was 100 t/h, which is normal. It seems that below 20mA, the station control always shows a value that is 0.08 mA too high... What could be the problem? How should this be addressed? Thank you!
“The “station control” has poor linearity, with zero offset and kinks. Given a 19mA signal, check what the flow offset is, and identify the inflection point. Then, plot the input-output curves. Next, write some short programs to process these curves: first perform a translation correction for the zero offset, then handle the deviation at the inflection points, and finally apply a scaling correction to the portion above those points. . . It’s done now. Send an red envelope to me, huh? Don’t expect to get something for free. {:2_42:}
I suddenly thought of creating a WeChat group for answering questions related to instruments – people would have to send red envelopes first before they could ask questions. Hahaha, what do you all think? . . The monkeys laughed, {:2_42:} {:2_40:} {:2_45:} {:2_30:} {:2_37:} {:2_36:}.
I’m leaving the scene for now; I’ll get back to you once there’s an update. I would also appreciate it if other experts who have encountered this phenomenon could share their insights: handshake
Bro Pig is still so enthusiastic: lol
There should be a setting current option in the flow meter; check the manual
Check the safety barrier (if any), switch to another channel, check the configuration settings of the control system, disconnect the cables, and send a signal directly to the control station for testing
If the measurement channels of the station control system are inaccurate, it is possible to calibrate those channels; if that doesn’t work, they need to be replaced. This is generally how DCS systems handle such situations