Common Faults and Simplified Troubleshooting Methods for Electromagnetic Flowmeters

Electromagnetic flow meters are commonly used flow measurement devices based on Faraday's law of electromagnetic induction. Composed of a sensor and a converter, they are widely used for flow monitoring of conductive media. In actual operation, due to factors such as installation and environment, the instruments are prone to malfunctions such as no display or exceeding the measurement range, affecting measurement accuracy and production continuity. Below, based on its working characteristics, we summarize the core causes of common malfunctions and simplify the troubleshooting process, providing practical guidance for operation and maintenance.

Working Principle and Structure

Electromagnetic flow meters measure flow based on Faraday's law of electromagnetic induction. Current flowing through the excitation coil generates a magnetic field. The conductive medium cuts the magnetic field, forming an induced electromotive force. After conversion by the sensor, the converter outputs a 4~20mA DC standard signal for display or control. Its core consists of a sensor and a converter, and it is available in integrated and separate types. The fault diagnosis logic is the same for both.

Common Faults and Simplified Troubleshooting Methods

I. Minimal or No Display

1. Core Causes:

Power supply, connecting cable, sensor/converter component damage; abnormal fluid flow; pipe inner wall adhesion problems.

2. Troubleshooting Steps:

Check the instrument alarm prompts. If there is no alarm, use a multimeter to check the power supply, switch, and fuse status.

Check the wiring of the excitation cable and signal cable for looseness and oxidation of the terminals. Tighten if necessary.

Disconnect the cables and use a multimeter to measure the resistance of the excitation coil (EX1, EX2 terminals) (typically 80~150Ω). The insulation resistance must be greater than 100MΩ. If damp, dry it.

Verify that the sensor arrow aligns with the fluid direction and confirm that the pipeline is full and the installation meets requirements.

Determine if the electrodes are contaminated by measuring the electrode contact resistance (difference ≤10%~20%) or polarization voltage (two values ​​close).

Suspect converter failure. Replace with a spare part of the same model for verification.

II. Instrument Displays Maximum (Over-Range)

1. Core Causes:

Signal circuit open circuit, incorrect wiring, incompatible sensor and converter; incorrect parameter settings; no fluid in the pipeline.

2. Troubleshooting Steps:

Short-circuit terminals A, B, and C of the converter. If the reading is zero, the fault is at the upstream end. Short-circuit the sensor output line. If the reading is zero, the cable is normal.

Measure the electrode resistance with a multimeter. Infinite resistance may indicate the pipe is not full of liquid; a normal empty pipe alarm should be triggered.

Use an analog signal to calibrate the instrument's zero point and full scale. Verify the pipe diameter, range, and other set parameters to confirm the sensor and converter are compatible.

Replace the converter circuit board to determine if the problem lies with the converter.

III. Instrument Reading Too High or Too Low

1. Core Causes:

Zero point not calibrated; improper sensor installation (insufficient straight pipe section, etc.); decreased electrode insulation resistance; cable insulation problems; air bubbles in the fluid.

2. Troubleshooting Steps:

Refer to historical data, compare with other flow meters, and estimate based on process material balance.

Check the sensor installation location to ensure the pipe is full of liquid, free of air bubbles, and the straight pipe section meets requirements.

Measure the electrode insulation resistance with a 500V megohmmeter (must be greater than 100MΩ). Clean the electrodes and the deposited layer on the inner wall of the pipe.

Verify the converter's zero point and full scale, check parameter settings, and verify cable grounding compliance.

IV. Instrument Display Fluctuations

1. Core Causes:

Electromagnetic interference, poor wiring contact; sensor dampness, electrode contamination; fluid pulsation, insufficient liquid in the pipeline.

2. Troubleshooting Steps:

Ensure sensor grounding resistance <100Ω; add grounding points if necessary; use matching signal cables and shorten the distance between the sensor and converter.

Shake the cable and tap the converter housing to check for loose or corroded terminals.

Dry the sensor junction box (insulation resistance ≥20MΩ), and clean scale from electrodes and inside the pipeline.

For fluid pulsation, move the sensor away from the pulsation source or install a damper; check for air bubbles in the pipeline.

V. Unstable Instrument Zero Point

1. Core Causes:

Uncalibrated zero point, decreased insulation in the measurement circuit; poor grounding, electromagnetic interference; insufficient liquid in the pipeline, slight fluid flow.

2. Troubleshooting Steps:

Use a megohmmeter to test the insulation resistance of the signal cable and sensor; promptly address any damaged seals.

Measure the electrode contact resistance when the pipe is full (difference ≤10%~20%), and measure the insulation resistance (≥100MΩ) after the empty pipe is dried.

Ensure the electromagnetic flowmeter sensor is independently grounded, kept away from high-power electrical appliances, and calibrate the instrument's zero point.

Check for full liquid conditions in the pipeline and eliminate minor fluid flow interference.

About Vacorda Instruments

Sichuan Vacorda Instruments Manufacturing Co., Ltd., established in 1996, specializes in industrial process measurement and control under extreme environments such as high temperature, high pressure, and strong corrosion. The company's main products include: level instruments, level switches, flow meters, pressure instruments, and temperature instruments.

Vacorda Instruments is driven by advanced technology research and development and guaranteed by strict quality control. From the careful selection of raw materials to the meticulous refinement of production processes, no detail is overlooked. Choosing Vacorda Instruments means choosing quality and trust!