There is a significant difference between the instrument readings and those displayed on the DCS system screen
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The DCS system integrator attributes the significant difference between the values shown on the field instruments and those displayed on the DCS system to issues with the system’s grounding and shielding. The data shown by the DCS system is slightly lower in all cases; if there were problems with the hardware or accuracy, the values would not be consistently low – only signal attenuation could cause such a situation. Is that the case?
It’s usually a grounding issue; check if the fluctuations are significant – if they are, then it’s definitely a grounding problem.
The signal fluctuations affected by grounding issues mean that you should first check the grounding system. Also, do you have any evidence to support the claim that all the signals you mentioned are low? Against which standard data are they being compared, and where do those standard values come from?
The variation is minimal; the readings shown on the thermoresistors and pressure transmitters in the field differ from those displayed on the DCS system by 1-2 degrees and 1-2 KPA.
Are the on-site gauge ranges consistent with those of the DCS? Inconsistencies will also lead to deviations
If the range and DCS settings are fine, it’s likely that there’s a problem with the transmitter
The range settings are all the same; the manufacturer says it’s a problem with signal attenuation
What is the distance from the field transmitter to the DCS? Is the signal cable shielded, and is single-sided grounding implemented? It’s normal for individual issues to occur; but it’s definitely not acceptable when everything is on the low side like in your case
Now they are all 4-20MA current signals, with very little attenuation. What brand of DCS are you using?
The simplest approach is to connect a 4-20mA transmitter directly to the control panel; if there is no deviation, it indicates a problem with the loop, while if there is a deviation, then the signal reception/transmission ends need to be checked.
There could be issues with grounding, interference, and the power supply as well; it’s possible that the capacity is insufficient or of poor quality