4-20mA Signal not changing

dshaw1612

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Join Date
Jan 2020
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I am trying to debug a pressure transmitter that outputs a 4-20 mA signal. Currently , the value is changing on the HMI screen and PLC depending on how fast we run a VFD, but when i put my multimeter in series with the output of the sensor, i get a solid 6mA no matter what. I know the value is changing in the PLC, but why am i not getting fluctuation on my measured value in the meter? Am i missing something
 
Are you sure it's 4- 20ma and not voltage output from the transmitter?

Can you post the complete catalog number of your transmitter?

Is this transmitter 2 wire loop powered or 3 or 4 wire?
 
We are using a 787 process meter

part # is ABB : 266dsh-e-s-s-a2-a1-v1-b2

it is 2 wire, and for sure doesn't output 0-10V
 
grasping at straws while looking for a "cause and effect" for the situation that you're reporting ... (the PLC and HMI signals are changing/updating - but the current reading on the series meter stays the same) ...

can you SAFELY break the loop for a quick test? ... if so, then disconnect the meter - and see if the signals in the PLC and the HMI drop out ... if they don't, then you've probably got the meter hooked into the wrong loop ...
 
Last edited:
Grasping at straws . . . me, too.

Unless you have the DVM set on an Amps scale so high that the resolution is only whole milliamps, like 0.006A instead of something like 6.27mA, 6,38ma, 6.09mA, I can't figure out how you get a variable reading on the HMI, but a constant reading on the DVM.

When you say you have the DVM in series, you've actually opened the loop circuit, removed a connection and inserted the DVM probes into that open connection?
 

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