Help with on-site instruments
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Our plant has several storage tanks equipped with pressure transmitters and remote level gauges; the on-site readings show 0, but the computer display shows the full scale. By measuring the current, it’s around 30 to 40 milliamps. Are all our meters broken, or is there a problem with the wiring?
It seems that some interference signals have gotten in. First, leave the scene and use a signal generator to send signals in order to identify the source of the fault
There’s a bit too little information. It’s recommended to specify the general type of instrument, all the contents that are displayed on-site, and other details; also, try measuring the current on-site
The maximum current of a 2-20mA transmitter should not exceed 23mA.
There is indeed not enough information to make an accurate judgment; it’s only possible to guess: 1. Check whether all these points are connected to the same module. If so, this situation occurring simultaneously might be due to a fault in the card; use a process verification instrument to send signals to check the card in order to confirm further； 2. If the same symptoms occur on different card assemblies simultaneously, check whether the instruments at the site have been exposed to water ； 3. If there is a safety barrier, check the input and output signals of the safety barrier first ； 4. If none of the above apply, then it’s necessary to check each instrument one by one to identify the fault points, such as checking the wiring, the shielding, and the grounding, etc
1. Pressure transmitters, as well as other instruments with a 2-wire 4–20mA output format, generally have an output current limit, that is, a protection current, which does not exceed 28mA. 2. The current values you are measuring now are 30 or 40mA, and there is a significant discrepancy between the instrument’s on-site display value and the output signal value. 3. So... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brother omitted 10,000 words {:3_51:}.
This post was last edited by 1111111 on 2017-9-26 at 13:27. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
First, determine whether the measurement is correct; if it is accurate, the problem lies in the transmitter unit. Check for any interference, then clear the waste fluid to see if the pipes are blocked. Finally, remove the transmitter for verification.
By the way, was the instrument calibrated in the workshop before installation? If it is not convenient to remove them, first test in the control room whether the channels of these two level gauges are functioning properly (safety barriers, clips, configuration). If there are no problems, then calibrate the lines. If there are no more issues, then we can break down the table and go back.
Check whether the pressure transmitter and level gauge indicators have been flooded with water. In the past, I encountered situations where the readings on the field instruments differed from those on the DCS, and this was due to water getting into the field instruments
Check whether the zero and full-scale output currents of the transmitter correspond to 4–20 milliamps, and verify that the wiring is correct. Use a signal generator to send 4–20 mA and see if the DCS functions properly. You need to determine whether the issue lies on-site or inside the cabinet, and then narrow down the search area.