Causes and Solutions of Abnormal Zero Point of Electromagnetic Flow Meter

The main causes of zero-point instability in an electromagnetic flow meter include a poor grounding system, partially filled pipes or air bubbles in the fluid, electrode surface contamination, converter zero drift, and external electromagnetic or environmental interference.

• Fluid-related factors: If the pipe is not completely filled with liquid or the liquid contains air bubbles, the zero point will fluctuate. Once the process conditions return to normal, the output value will stabilize.

• Valve leakage: Over time, worn or contaminated valves may fail to seal properly, also leading to zero-point instability.

• Changes in fluid conductivity: Variations or uneven distribution of conductivity can cause zero drift when the fluid is static and output fluctuations when it is flowing.

• Poor grounding: Improper grounding may cause instability. The meter’s grounding wire should not be connected to shared grounding systems such as motors, electrical devices, or water pipes. If the converter is already grounded through its cable, avoid additional grounding to prevent potential differences that cause interference.

• Scale buildup or deposits: If solids are present in the fluid or scale accumulates on the inner wall of the measuring tube, zero-point instability may occur. Regular cleaning of the inner wall deposits and recalibration when necessary can resolve the issue.

• Insufficient insulation: Poor insulation, often caused by weak signal cable insulation or loose wiring terminals, can result in unstable zero readings. Proper insulation of the instrument and signal lines is essential for stability.

1. The pipeline is not filled with liquid, or the liquid contains bubbles

Solution:

A. If the liquid in the pipeline is not full, the electromagnetic flow sensor should be moved to a full position when it is installed horizontally; When the electromagnetic flow sensor is installed vertically, the liquid flow should be from bottom to top.

B. If there are bubbles in the pipeline, install getter or automatic exhaust valve upstream of the sensor.

2. Zero instability of electromagnetic flowmeter is caused by tiny flow in pipeline

The pipeline shut-off valve has poor air tightness, which misunderstands the tiny leakage measured by electromagnetic flowmeter as the unstable zero point of flowmeter 

a. The valve has poor air tightness due to long service time or dirty liquid

b. Besides the main pipeline, there are several branch pipes, forgetting to close the valves of the branch pipes

3. External interference such as stray current will lead to zero instability

a. Eliminating external interference such as stray current in pipeline mainly depends on good grounding of electromagnetic flowmeter. Generally, the grounding resistance is less than 10ω. What's important is that it can't be grounded with other electrical appliances.

b. When the flow sensor is installed on the plastic pipe, the pipe with insulating coThe sensor should be far away from the motor, engine and other devices that may cause interference.ating and paint. It is necessary to install grounding rings at both ends of the sensor to ensure sufficient contact between the measured medium and the sensor housing. Ensure the normal operation of electromagnetic flowmeter.

c. Magnetic flow sensors should be kept away from motors, engines and other equipment that may cause interference.

4. The conductivity of the measured medium is uneven

Install the flow sensor in a place with constant or uniform conductivity, avoid being close to the dosing point, and avoid installing the flowmeter downstream of the pipeline with insufficient chemical reaction.

5. Low conductivity will cause zero drift

6. The insulation of the instrument signal line is reduced

Insulation of signal lines and their terminals is reduced due to moisture, water, acid mist, etc.

Zero drift in an electromagnetic flow meter is not an unsolvable issue. By taking proper measures—such as regular calibration, optimizing the installation environment, and using temperature compensation technology—you can effectively minimize zero drift, ensuring accurate measurements and long-term system stability.