Calibration of bubbler or purging method level transmitter

What is bubbler level transmitter?

The level bubbler transmitter can be used to start an airburst backwash and check the in-take screens for debris. A dip tube is placed on either side of the screen to do this, and a backwash may be started to clean the screens once the pressure differential between the two reaches a certain level. The name of this system is a Differential Level Bubbler.

  • To regulate the intake pumps, the level of the wet well may be measured using the level bubbler transmitter.
  • Including sanitary waste stations, the level bubbler transmitter may be used to measure levels in various kinds of liquids.
  • Ultrasonic level transmitters can be retrofitted with the level bubbler transmitter in place of them.

How to calibrate DP type level transmitter?

Purpose and Scope:

This procedure’s detailed description explains how to calibrate a bubbler method level DP transmitter using standards that are positioned nearby to the process.

Tools required for DP transmitter calibration:

Calibration of bubbler or purging method level transmitter1
  • Hand tools that are required.
  • Calibrator for Standard Low Pressure Use.
  • Standard Multimeter.
  • Leads and probes for performing tests.
  • tubes, as well as the typical fittings
  • A soft cloth for the purpose of cleaning.


  • Please click on the link that has been supplied in order to have a better understanding of the fundamental safety, general guidelines, and calibration activities that are involved in process industries.

Fundamental Health and Safety Considerations Regarding the Calibration Process Used in the Process Industry

  • Request that the panel operator switch the controller to manual mode for the bubbler method level control loop, and set it to MOS (Maintenance override switch) for the ESD loop. Both of these settings should be done simultaneously.
  • Locate the DP type bubbler method level transmitter that you wish to calibrate. Verify that the level transmitter is a bubbler method DP type, and make a note of and double-check any crucial information, such as the Tag number (e.g., the manufacturer, model number, pressure range, etc.).
  • Depending on the kind of system, you might need to depressurize the system’s impulse tubes as well as the bubbler method level transmitter before calibrating the bubbler method level transmitter. Depressurize the system using the proper methods (such as by shutting off the instrument air header‘s main purge air inlet pressure or purge gas supply system).
  • Do not cut off the power to the level transmitter, using an instrument loop diagram check any adjacent junction boxes or Marshalling Cabinet close to the control room to see whether the power supply is available at the source.
  • This procedure may need to be changed depending on equipment and process location of the bubbler method level transmitter.
  • Always follow manufacturer instructions and local safety standards while using bubbler method level DP type level transmitters or other process equipment.
  • Follow lockout/tagout procedures to prevent accidental starts. Keep the bubbler method DP-type level transmitter away from the process.

Calibration Setup for Bubble method DP type level transmitter

Calibration of bubbler or purging method level transmitter2
  • The calibration equipment’s process area must not have electromagnetic interference or vibrations. It must be well-ventilated and lit.
  • Gather all required tools and equipment.
  • The calibration equipment’s process area must not have electromagnetic interference or vibrations. It must be well-ventilated and lit.
  • Gather all required tools and equipment.
  • Close the HP and LP isolation valves on the transmitter manifold while opening the equalizing valve.
  • Open the drain plugs on the HP and LP sides of the level transmitter to drain any remaining process fluid.
  • After removing the HP and LP side impulse lines from the transmitter manifold, thoroughly clean the fittings and any remaining fluid inside the transmitters.
  • Make that the HP & LP pressure ports on the bubbler method level transmitter are dry.
  • The high pressure side (HP) of the DP type level transmitter should be attached to one end of the pvc calibration tube and the output of the low pressure calibrator should be connected to the other. Examine the connections to make sure they are secure and free of leaks.
  • The low-pressure side (LP) of the bubbler technique level transmitter is always maintained open to the atmosphere.
  • Make a series connection between the multimeter (mA mode) and an analogue input loop between the junction box and the bubbler method DP type level transmitter using probes and a lead.
  • If the transmitter is a smart type, the HART field communicator should also be linked to the bubbler method level transmitter terminal.
  • As shown in the diagram, the connections have been made and are presently being ready for the calibration of the bubbler method level transmitter.

Calibration procedure

  • The bubbler technique level transmitter’s tubing and wire connections should be checked for stability.
  • Open the cover on the bubbler method level transmitter terminal and make that the terminal has a power source of 24 VDC.
  • By reviewing the instrument data sheet for the level transmitter that uses the bubbler technique, you may verify a number of the parameters. The tag number, fluid specific gravity, LRV, and URV are typical characteristics.
  • If it’s a smart transmitter, you may use a HART communicator to check the parameters.

Example calibration

Calibration of bubbler or purging method level transmitter3
  • The tank’s size, the specific gravity of the process fluid, and the ends of the transmitter’s HP and LP impulse tubes may all be used to determine the LRV and URV.
  • The transmitter’s LRV and URV, for instance, are established as described below if the bubbler level transmitter is mounted as shown in the calibration setup image above.

LRV = Lower-range value (a measurement that’s output is 4 mA).

URV = Upper-range value (a measurement with a 20 mA output).

SG = A liquid’s specific gravity (relative density). Water has a specific gravity of 1.00 in both traditional and SI systems.

HW= Equivalent Headlevel pressure of Water

H = Height of the bubble tube immersed inside the process liquid

H = Tank level need to be measured.(head between LRV and URV)

H1 = Head level below minimum level (suppression)

Differential pressure (DP) = HP -LP

H = 3000mm

H1 = 200mm

SG = 0.84

At zero percentage of level (for 4mA output) the LRV is

DP (HW) = HP – LP

DP = (H1*SG) – 0

DP = (0.84 * 200) – 0

DP = 168

So LRV of the transmitter is (At 4 mA) = 168mmH2O

At 100 percentage of level (for 20mA output) the LRV is

DP (HW) = HP – LP

DP = {(H1*SG) + (H*SG)} – 0

DP = {(0.84 * 200) + (0.84*3000)} – 0

DP = 168+2520-0

DP = 2688

So URV of the transmitter is (At 20 mA) = 2688mmH2O

Calibration Range of the transmitter = 168 to 2688 mmH2O

  • Set the 0% Lower Range Value (LRV) of the bubbler type level transmitter as the LRV for the calibration range. Set the level transmitters’ span’s upper range value (URV) for the calibration range to 100%.
  • Apply the pressure calibrator’s LRV 0%, or 168mmH2O, to the transmitter’s high pressure side while leaving the low pressure side exposed to the atmosphere.
  • A 4mA output from the transmitter should be shown on the multimeter at this point.
  • Find the zero adjustment on the bubbler type level transmitter and make the necessary changes until the reading indicates 4 mA if the 4 mA reading is not shown on the display. Alternatively, use the HART Communicator to make the required modifications for the smart transmitter.
  • Apply pressure to the bubbler type level transmitter’s high pressure side to raise the reading to the 100% higher value (URV), or 2688mmH2O.
  • Focus on the 20mA reading on the multimeter while making any necessary adjustments to the SPAN adjustment option in the display or the SPAN adjustment potentiometer of the DP level transmitter. This is the bubbler type transmitter’s URV output.
  • Until the Bubbler type level transmitter is calibrated to the acceptable tolerance, the calibration procedure must be done as often as necessary.
  • Depending on the specific pressure calibrator and level transmitter of the bubbler type being used, the calibration technique may change. Therefore, before beginning, make sure you adhere to the manufacturer’s instructions.

Recording calibration

  • To confirm that the bubbler type DP level transmitter is producing the required output values, measure the linearity of the output at 0%, 25%, 50%, 75%, and 100% in both the upscale and downscale directions.
  • If the output value does not fall within an acceptable range, calibration is required. It is necessary to repair or replace the bubbler type DP level transmitter if the output values have once again strayed outside of the permissible range.
  • The bubbler type DP level transmitter does not require further calibration if all output values (+/-%) are within acceptable tolerances.
  • The output information should be written in the as found/as left column of the blank calibration report to prepare the calibration report.

Completion of calibration

  • Once the calibration has been successfully accomplished, affix the calibration label on the bubbler type DP level transmitter.
  • After the calibration is complete, clean the test equipment, store it securely, and note the calibration data for subsequent use.
  • Take away the low pressure calibrators, the DP level transmitter of the bubbler type, and the other calibration equipment.
  • The connections for the DP level transmitters of the bubbler type must be fixed back in the processing area.
  • Check to see if the workplace has been kept clean.
  • De-isolate the equipment and re-establish normal air pressure in the instrument air header or purge gas supply system.
  • Restore the bypassed or suppressed signal of the bubbler type DP level transmitter to its original level.
  • Make sure the bubbler type DP level transmitter is in good working order before using it.

Sample calibration report

The next figure demonstrates how the bubbler type DP level transmitter sample report was calibrated in a process area using a pressure calibrator and multimeter as the reference.

Calibration of bubbler or purging method level transmitter5

Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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