1、 The signal is getting smaller and smaller (gradually decreasing)

This situation is usually related to electrode adhesion, lining damage, or slow changes in process conditions. Main reasons and solutions:

1. Electrode scaling or adhesion of insulation layer (the most common cause) • Reason: Oil, viscous substances, solid particles, bubbles, etc. in the measured fluid gradually deposit on the surface of the electrode, forming an insulation layer or cover layer, resulting in an increase in electrical contact resistance between the electrode and the conductive fluid, and a decrease in signal strength.

• Judgment: Measure the insulation resistance of the electrode (requires specialized instruments, conducted under power-off conditions) or check the contact resistance between the electrode and the liquid online (depending on the instrument function). The signal decline is usually synchronized with the accumulation process of attachments.

• Treatment: • Electrode cleaning: Choose the appropriate cleaning method according to the working conditions, such as mechanical cleaning (using a soft cloth or brush), chemical cleaning (injecting specialized cleaning agents to dissolve dirt), ultrasonic cleaning, or high-pressure water flushing.

• Prevention: Choose scraper or detachable electrodes and regularly maintain and clean them.

2. Lining wear, scaling, or deformation • Reason: • Wear: The fluid contains solid particles, and long-term erosion causes the lining to become thinner or damaged, changing the magnetic circuit structure.

• Scaling: The lining surface has a thick layer of insulation scale, which is equivalent to increasing the insulation distance of the signal line, resulting in signal attenuation.

• Deformation (bulging): Under high temperature or negative pressure conditions, the lining may peel off from the pipe wall, bulge, causing electrode displacement or even short circuit.

• Judgment: Stop the machine and check the condition of the lining inner wall.

• Treatment: Replace damaged or severely scaled lining. Select suitable and more durable lining materials (such as ceramic lining) based on fluid characteristics.

3. Changes in fluid characteristics • Reason: • Decreased conductivity: The fluid conductivity slowly decreases to near the minimum required value of the flowmeter, resulting in unstable and attenuated measurement signals.

• Increase in solid/gas content: The content of solid particles or bubbles in the fluid gradually increases, causing an increase in signal noise and effective signal attenuation.

• Judgment: Analyze whether the composition and conductivity of the fluid have changed.

• Processing: Confirm that the fluid parameters meet the requirements of the flowmeter and stabilize the fluid properties from a process perspective.

4. Environmental reasons: Decreased insulation performance of cables. Reason: The insulation layer of signal cables has decreased in insulation performance due to long-term moisture, high temperature, or aging, resulting in signal leakage to ground and signal weakening.

• Judgment: Measure the insulation resistance of the cable.

• Solution: Replace the shielded signal cable with a new one and ensure that the cable joint is well sealed.

2、 Sudden signal drop (sudden malfunction)

This situation is usually related to circuit faults, process changes, or mechanical damage. Main reasons and solutions:

1. Reasons for the process system • Reasons: • Pump failure: The impeller of the pump is damaged or corroded, causing a sudden drop in actual flow rate.

Valve misoperation: The upstream valve is mistakenly closed or closed.

• Pipeline blockage: The pipeline or filter is blocked by foreign objects.

• Insufficient pipeline: Air pockets or liquid not filling the pipeline (this is a major taboo for electromagnetic flow meters).

• Judgment: This is the primary point of investigation! Check the system pressure, pump operation status, valve opening, and whether the pipeline is filled with liquid.

• Handling: Eliminate process faults to ensure that the pipeline is full and the flow is stable.

2. Excitation system failure • Cause: Short circuit or open circuit of the excitation coil, or failure of the power/circuit board supplying power to it, resulting in a sharp decrease or disappearance of magnetic field strength. Without a magnetic field, it is impossible to generate induced electromotive force.

• Judgment: Measure the resistance value of the excitation coil (compared with the factory value or normal value), and check whether the excitation current is normal.

• Handling: Repair or replace the excitation coil or corresponding circuit board. It needs to be carried out by professionals.

3. Electrode related faults • Causes: • Electrode circuit open circuit or short circuit: Loose or disconnected electrode leads, or insulation damage causing a short circuit between the electrode and the grounding pipe wall.

• Electrode covered: Sudden dirt (such as plastic bags, large impurities) covers the electrode.

• Judgment: Measure the resistance of the electrode (the resistance should tend to infinity when empty), or use the "electrode check" function of the instrument.

• Handling: Tighten the leads, clean the coverings, and repair the insulation. If the electrode itself is damaged, it needs to be replaced.

4. Converter malfunction • Cause: Damage to electronic components such as signal amplifiers and CPUs.

• Judgment: This is the final factor to consider. After excluding all external factors, the "replacement method" (replacing with a known normal converter) is used to determine.

• Handling: Send for repair or replace the converter.

Summary of systematic troubleshooting steps

Suggest conducting inspections in the following order of "from outside to inside, from easy to difficult": 1. Confirm the process condition (primary step!): • Check if the pipeline is full? Is there a large amount of bubbles present?

Confirm if the pump, valve, and filter are working properly? Has the actual traffic really decreased? (can be judged by other reference indicators)

Has there been a significant change in fluid composition and conductivity?

2. Check the wiring and power supply: • Check if the wiring terminals of the signal cable and excitation cable are loose, corroded, or have water ingress?

Check if the power supply voltage is normal?

3. Utilizing the self diagnostic function of flow meters: Modern intelligent electromagnetic flow meters typically have rich self diagnostic and parameter checking functions. Refer to the manual and check if the alarm information, excitation current, electrode resistance, and other parameters are normal.

4. Offline detection (after shutdown and emptying of the medium): • Electrode resistance measurement: Measure the resistance between two electrodes, as well as the resistance of each electrode to ground, and compare it with the typical values in the instrument manual.

Measurement of excitation coil resistance and insulation resistance: Compare with factory records to determine the condition of the coil and insulation.

Lining inspection: visually inspect the lining for integrity, wear, and knots