Question regarding the gas alarm signal! Please advise!
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Many of our gas detectors show a reading of 0 at the site, but the DCS displays values of -0.1, 0.2; in some cases it even shows 0.9. What could be the possible reasons for this? Doesn’t the current decrease due to long-distance transmission? Please help analyze the possible reasons. We think one reason might be that the precision of the on-site indications is not high enough; as a result, the actual output current during on-site verification might be lower, but this value is ignored. However, some meters do show an output of 4 mA when measured on-site, and the control panel also displays a negative value. It’s unclear why this happens
Have you checked whether the signal that reaches the control room from the site is consistent with that at the site? You can definitely determine the problem using standard instruments.
My suggestion is to measure this current value simultaneously at the site and in the control room to check whether they are equal. If the currents differ, there is interference or current leakage; it is necessary to examine the grounding of the cable’s shielding layer, the cable’s insulation resistance, as well as the resistance values between the various conductors, to determine if aging or other issues are at fault. Furthermore, the precision shown on the host computer should not be too high; generally, one decimal place is sufficient.
Thank you! The current level on the DCS side is lower than that outside; it’s indeed possible that this is caused by interference or current leakage. Improving the grounding of the cables should help resolve the issue! We have also considered that it might be due to excessive precision on the system side. Thank you for your help