Field Instrumentation

Various issues in DP Transmitter & How to Troubleshoot it?

What is a Differential Pressure Level Transmitter?

A Differential pressure transmitter is an electrical device or pressure measuring device used to measure the level in the tank or vessel. It is used to measure the difference in the pressure in the container.

Parts of the Differential Transmitter
Differential Transmitter Parts

Introduction of Differential Pressure Transmitter problems:

While in service for a long time, DP transmitters cause a malfunction in their performance. To troubleshoot and find possible causes of malfunction of the transmitter is difficult. During troubleshooting the DP transmitter, it is important to verify the manufacturer’s manual. By reading the manufacturer’s manual, we can able to find the malfunctioning parts of the DP transmitter. If some malfunction is found it can be rectified immediately. Some malfunctions are common in all DP transmitters. They are listed below:

Also Read: What is a differential pressure flow meter and what are its types?

DP TRANSMITTER LOW OR NO OUTPUT OR HIGH OUTPUT PROBLEMS:

Sensing Element Issues:

Physical restriction or insulation damage

Solution for DP Transmitter showing Low or no output or high output due to Physical restriction in sensing element:

  • Check the physical condition and clean the sensing element if some obstruction is found.
  • Check the insulation of the sensing element and replace the transmitter with a new one if damage were found
  • Check manufacturer manual to disassemble and rectify the sensing element issue or contact the manufacturer

Loop wiring Issues:

DP Transmitter is not providing actual value due to loop wiring issues

Solution for DP transmitter Loop wiring Issues:

  • Check whether the required voltage is supplied to the transmitter
  • Check the current supplied to the transmitter is adequate
  • Check for any short circuits or grounds in the loop wiring
  • Check for proper termination of polarity at the transmitter end

Impulse Piping Issues:

DP Transmitter is providing invalid output due to impulse pipe in the DP transmitter.

Solution for DP transmitter Impulse Piping Issue:

  • Check the physical condition and clean the sensing element if some obstruction is found.
  • Check the insulation of the sensing element and replace the transmitter with a new one if damage were found
  • Check the manufacturer manual to disassemble and rectify the sensing element
  • The density level in the impulse piping remains unchanged in the DP transmitter to obtain an accurate signal.
  • Check for any choking in the impulse line on both the HP side and LP side which will cause invalid pressure measurement, if choking is found isolate the DP transmitter from the process line and clean the impulse tubing.

Pressure Source Issues:

Invalid measurement due to No balanced pressure source.

Solution for Pressure Source Issue:

  • Check the leakage in the vessel.
  • Check the pressure source in the proper level or zero condition in the ideal condition.
  • Check the pressure source in the vessel.

CALIBRATION PROBLEMS IN DP TRANSMITTER:

Electronic Issue:

Electronic issue due to PCB panel complaint and terminal connection issue.

Solution for Electronic Issue:

  • If an electronic issue occurred, the panel to be isolated from the terminal and a new electronic panel to be connected
  • Check for any loose connections in the existing termination and rectify it by cleaning the terminals and connecting the wires properly

Output Voltage Issues:

Sometimes the output voltage will be below 1V at the transmitter.

Solution for Output Voltage Issue:

  • Check whether the power output voltage is in the range of 1V to 5V in the transmitter, if not replace the PCB/transmitter as per the user manual.

DP transmitter Indicator Issues:

Transmitter shows error reading due to fault in the meter.

Solution for Output Voltage Issue:

  • Check for any fault indication LEDs in the transmitter and try to troubleshoot it as per the transmitter user manual.
  • If local troubleshooting fails then replace the transmitter with a new one and contact the Manufacturer.

DP TRANSMITTER ERRATIC OUTPUT PROBLEMS:

Process Pulsation Issues:

Damping is the process of adjusting of time required in addition to the updated output time to get the final output value in the transmitter. Due to the unscheduled time constant in damping, the output varies in the transmitter.

Solution for Output Voltage Issue:

  • Adjust the scheduled damping time between 1 to 32 seconds in the transmitter to get the final output in the transmitter.

Grounding Problem Issue:

The signal received in the output is lower than the reading displayed due to voltage drop in the differential pressure transistor.

Solution for Grounding Issue:

  • The above problems can be prevented by providing clear grounding using heavy gauge wires in the power system.

LEVEL MEASUREMENT PROBLEMS IN DP TRANSMITTER:

Blockage issue:

Blockages in the flow of water due to the contamination block the sensing elements that affect the measurement of the transmitter and show error output in the display of the pressure level transmitter.

Solution for Blocking Issue:

High-Pressure Issues:

Due to the high pressure of flow leakages in the valve occurs in the DP transmitter.

Solution for DP transmitter high-pressure Issue:

  • Concealed piping system to be provided in all the junction of the flow valves and isolation valves which avoid the leakages

Freezing Issues:

During Cold weather condition in the external environment, the flow in the vessel get frozen due to external contact.

Solution for Freezing Issue:

  • To avoid the freezing of the sensing element, surface heating is to be provided.

NOISE PROBLEMS IN DP TRANSMITTER:

Noise Issue:

During the process of the flow of the fluid, vibration arises in the sensing element for a long period of use or at a very high pressure of the flow and similarly, noise arises in the vessel due to oscillation in the process of flow in the tank.

Solution for Noise Issue:

  • A low pass filter in the sensing element which reduces high frequency arises in the vessel and noise will be completely reduced in the Pressure Level transmitter.

Precautions to be followed while troubleshooting DP Transmitter:

  1. Before opening any impulse tubing for troubleshooting the DP transmitter, we should isolate the transmitter properly from the process and de-pressurize it using an equalization valve from the transmitter manifold.
  2. Touching the diaphragm of the pressure transmitter is to be avoided.
  3. The transmitter should be temperature protected to prevent freezing in the measuring medium.
  4. Before isolating the instrument from the transmitter, the power supply to the transmitter is cut off.
  5. Manufacturer’s manual to be read carefully about the pressure level transmitter and their cause for malfunctions.

Regular periodical maintenance of the pressure transmitter avoids many causes of malfunction.

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