dP Flow Meter Troubleshooting Guide
When dealing with differential pressure (DP) flow meters, troubleshooting can be essential to maintaining accurate and reliable measurements in various industries. DP flow meters are widely used for measuring fluid flow rates, but like any equipment, they can encounter issues that affect performance. Whether it’s seemingly incorrect readings, flow obstructions, calibration errors, or pressure drops, identifying and resolving these issues quickly is crucial for minimizing downtime and ensuring optimal operation.
Detailed below is a comprehensive guide to troubleshooting more common problems with DP flow meters, helping you pinpoint issues and implement effective solutions.
Problem: Low or No Output
| Potential Cause | Corrective Action |
| Primary Element | • Check the installation and condition of primary element depending on what type of DP device is being used. Contact PFS once you have information on the device and we can provide a complete inspection process for you to follow. • Check for sufficient upstream straight length of pipe without change in direction, diameter, etc. |
| Loop Wiring | • Check for adequate voltage to the transmitter. • Check the mA rating of the power supply against the total current being drawn for all transmitters/devices being powered. • Check for shorts and multiple grounds. • Check for proper polarity at the signal terminal. • Check loop impedance (should not exceed the specification for your plant). • Check wire insulation to detect possible shorts to ground. |
| Impulse Piping | • Ensure that the pressure connection is not reversed. • Check for leaks or blockage. • Check for entrapped gas in liquid service or entrapped liquid is gas service. • Check for sediment or debris in the DP transmitter process flange. • Ensure that blocking valves are fully open and that bypass valves are tightly dosed. • Ensure that density of fluid in impulse piping is unchanged. |
| Sensing Element (transmitter sensor) | • The sensing element is not field repairable and must be replaced if found to be defective. • Disassemble the transmitter and probe further (check your manufacturer’s manual for instructions on how to disassemble your transmitter). • Check for any obvious defects/damage such as dents or punctures in the diaphragms. At this point you may need to contact your manufacturer if there are any defects in the sensing element. |
Problem: DP transmitter does not calibrate properly
| Potential Cause | Corrective Action |
| Pressure Source/Source Connections | • Check for restrictions or leaks in the calibrator connections. • Check for proper leveling or zeroing of the pressure source. • Check to see if temperature change has affected the pressure readings. • Check weights/gauge to ensure proper pressure setting. • Determine if your pressure calibrator has sufficient accuracy. |
| Meter | • Determine if the transmitter & calibrator are functioning properly. |
| Power Supply | • Check the power supply output voltage at transmitter. |
| DP Transmitter Electronics | • Make sure the transmitter connectors are clean. • Check the D/A (digital to analog) conversion by performing a D/A trim with a calibrated multimeter in series with the field wiring. If the electronics are still suspect, substitute with new electronics. |
| Sensing Element (transmitter sensor) | • The sensing element is not field repairable and must be replaced if found to be defective. • Disassemble the transmitter and probe further (check your manufacturer’s manual for instructions on how to disassemble your transmitter). • Check for any obvious defects/damage such as dents or punctures in the diaphragms. At this point you may need to contact your manufacturer if there are any defects in the sensing element. |
Problem: High / Low Output
| Potential Cause | Corrective Action |
| Primary Element | • Check for restrictions at primary element. |
| Impulse Piping | • Check for leaks or blockage. • Check for entrapped gas in liquid service. • Check for sediment or debris in the DP transmitter process flange. • Ensure that blocking valves are fully open and that bypass or equalization valves are tightly closed. • Ensure that density of fluid in impulse piping is unchanged. |
| Power Supply | • Check the power supply output voltage at transmitter. |
| DP Transmitter Electronics | • For Flow application make sure square root extraction is applied once in the transmitter/PLC/SCADA etc. If the square root transfer function is not applied at all the flow reading will be lower than actual. If square root is applied twice the flow reading will be higher than actual. • Make sure the transmitter connectors are dean. If the electronics are still suspect, substitute v1ith nev1 electronics |
| Sensing Element (transmitter sensor) | • The sensing element is not field repairable and must be replaced if found to be defective. • Disassemble the transmitter and probe further (check your manufacturer’s manual for instructions on how to disassemble your transmitter). • Check for any obvious defects. At this point you may need to contact your manufacturer if there are any defects in the sensing element |
Problem: Erratic Output
| Potential Cause | Corrective Action |
| Loop Wiring | • Check for adequate voltage to the transmitter. • Check for intermittent shorts, open circuits and multiple grounds. |
| Process Pulsation | • Adjust damping. |
| DP Transmitter Electronics | • Make sure the transmitter connectors are clean. If the electronics are still suspect, substitute with new electronics. |
| Impulse Piping | • Check for entrapped gas in liquid lines and for liquid in gas lines. |
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