How much do gas bubbles from dissolved air affect the accuracy of the LGF-PA66 electromagnetic flowmeter?

An electromagnetic flowmeter measures the volume flow of the liquid. Bubbles entering the measuring tube displace liquid and change the impedance of the conductive path between the electrodes; the result is a fluctuating or high reading, and how bad it gets depends on the gas fraction and the bubble pattern.

Uniform microbubbles below about 1% gas volume have a negligible effect on the LGF-PA66. As the gas fraction rises the reading turns unsteady; above roughly 5% the error becomes significant, and in severe cases the value jumps sharply and the empty-pipe alarm may trigger. Occasional large slugs are worse than uniform microbubbles — the signal dips the moment a slug sweeps past the electrodes.

Deal with it on site in this order:

• Find where the gas comes from first — air drawn in through a pump suction leak or a negative-pressure section is the most common cause. Fix the leak before worrying about accuracy.
• Mount the meter on a pressure-stable section such as a pump discharge, away from the highest point of the line, sudden enlargements and sharp bends; add an air-release valve upstream if needed.
• On vertical pipes run the flow upward so bubbles rise through and do not linger in the measuring tube.

The LGF-PA66 has built-in empty-pipe detection. During commissioning set the empty-pipe threshold against the actual conductivity of the medium, so that gas locking or a dry line raises an alarm on the platform immediately instead of feeding bad data into statistics. For more information, please visit our product page or contact our technical team.