This article describes the troubleshooting guidelines for the common problems with a DP-type flow transmitter. The DP transmitter is used as a differential pressure transmitter, flow transmitter, and level transmitter.
Differential pressure type flow transmitter is a widely used flow transmitter. DP-type flow transmitter is generally used in liquid and gas service flow measurement which are clean in nature.
We encounter many problems with the DP-type flow transmitter in our day-to-day routine activities. Let us see some common problems and their troubleshooting steps in this article.
DP type Flow Transmitter Troubleshooting Guidelines
Some common problems in DP-type pressure transmitters are :
Let us see the troubleshooting guidelines for the problems mentioned in the above chart for DP type flow transmitter
Follow the below-mentioned steps to troubleshoot the problems of the DP type Flow Transmitter.
1. DP-type flow transmitter in the power-off condition
DP type flow transmitter can be in power-off condition due to a few reasons like cable issues or fuse issues or barrier issues. First, check the cable connection in the DP type flow transmitter. All the connections should be proper with the proper type of lugs. Then check the voltage using a properly calibrated Multimeter.
If no voltage is found, then check the connections in the junction box and the marshaling cabinet. Do proper cable tightening and/or proper lugging if found any problem with that. Check the condition of the fuse in the marshaling cabinet. If the fuse is not ok, then replace the fuse with a fuse of a similar rating. Check the barrier. If the barrier is faulty then replace the barrier. Also, Check the cable healthiness.
2. Flow value mismatch in field and PLC/DCS
Generally, the issue of flow value mismatch in the field transmitter as well as in the PLC/DCS is due to incorrect range configuration on both sides. Verify the range in the field transmitter as well as in the PLC/DCS. The datasheet will contain the correct range of the flow transmitter which should be configured on both sides.
3. Flow value mismatch in field and PLC/DCS
- DP type flow transmitter not showing the proper value
- Check the condition of the process isolation valves of the DP type flow transmitter. Both the HP and LP side isolation valve should be in open condition.
- Check the condition of the manifold. The equalization valve of the manifold should be in close condition. Both the isolation valves in the manifold should be in open condition. The vent ports in the manifold should be properly fixed.
- Check all the tubing connections. No leakage should be present from any of the fittings. No tube should be in punctured condition. Attend the tube leakage (whether major or minor) and/or replace the punctured tube after properly isolating the DP type flow transmitter.
- The tubes can be in a chocked condition also. Flushing or closed drain flushing is required to do proper dechoking of the tube. If the flushing of the tube does not work, then use a pump to dechoke the tube. Maximum pressure should be 1.5 times the pressure of the process fluid while dechoking the tube with a pump.
- Verify whether the HP side of the transmitter is connected to the HP side of the tapings in the line. Also, check the LP side of the transmitter is connected to the LP side of the tapings in the line. If found swapped, then correct the tubing connection.
- If any force is present in the field transmitter or in the PLC/DCS, then the value will remain constant. Remove the force after taking proper approvals or following the interlock restoration procedure.
- Only one side should have a square root function. The square root function should be either in the field transmitter or in the PLC/DCS. If the square root is on both sides, then the value of the flow will be totally incorrect.
- Check the calibration of the DP type flow transmitter. If calibration of the DP type flow transmitter is disturbed, then do Zero and Span setting as per the standard procedure.
- Check all the necessary configurations like LRV, URV, mA range, and device address if any as per the datasheet of the DP type flow transmitter.
4. DP type flow transmitter value fluctuating
- DP type flow transmitter value fluctuating
- Check for tube leakages. Minor tube leakage can also cause fluctuation in the reading of the DP type flow transmitter. Attend the leakage.
- Do flushing of the DP type flow transmitter. Because of any air bubble trapped in the line also, the value of the flow will fluctuate.
- Increase the damping factor in the DP type flow transmitter if the fluctuations are very high.
