There are two common failures of electromagnetic flowmeters in operation: one is the failure of the meter itself, that is, the failure caused by the damage of the instrument's structural parts or components; the other is the failure caused by external causes, such as improper installation, flow distortion, deposition, and structure. Scum etc. We discuss these two types of failures.

1. The meter has no flow signal output

1. Reason analysis

This type of failure is more common during use, and the reasons are generally: (1) the power supply of the instrument is not normal; (2) the cable connection is not normal; (3) the fluid flow condition does not meet the installation requirements; (4) the sensor parts are damaged or measured There is an adhesion layer on the inner wall; (5) The converter components are damaged.

2. Solution

(1) Confirm that the power supply has been connected, check whether the output voltage of the power supply circuit board is normal, or try to replace the entire power supply circuit board to judge whether it is good or bad.

(2) Check whether the cable is intact and the connection is correct.

(3) Check the direction of liquid flow and whether the liquid in the tube is full. For the electromagnetic flowmeter that can measure forward and backward, it can be measured if the directions are inconsistent, but the set display flow does not match the positive and negative directions and must be corrected. If the workload of dismantling the sensor is large, you can also change the arrow direction on the sensor and reset the "flow direction selection" item of the display instrument. The underflow of liquid in the pipeline is mainly caused by the improper installation position of the sensor. Measures should be taken during installation to avoid causing the liquid in the pipeline to be unfilled.

(4) Check whether the electrodes on the inner wall of the transmitter are covered with a liquid scarring layer. For measuring liquids that are prone to scarring, clean them regularly.

(5) If it is judged that the fault is caused by the damage of the converter components, replace the damaged components.

2. Output value fluctuation

1. Reason analysis

This type of failure is mostly caused by the influence of the measuring medium, installation conditions or the external environment. The failure can be eliminated by itself after the external interference is eliminated. In order to ensure the accuracy of the last two measurements, such failures cannot be ignored. In some production environments, due to the large vibration of the measuring pipe or liquid, the circuit board of the flowmeter will become loose and the output value may fluctuate.

2. Solution

(1) Confirm whether it is the cause of the process operation and the fluid does pulsate. At this time, the flowmeter only reflects the flow condition truthfully, and the fault can be eliminated by itself after the pulsation ends.

(2) Electromagnetic interference caused by external stray current. Check whether there are large electrical appliances or electric welding machines working in the operating environment of the instrument. Make sure that the instrument is grounded and the operating environment is good.

(3) When the pipe is not filled with liquid or the liquid contains bubbles, both are caused by the process. At this time, you can ask the technician to confirm that the output value can return to normal after the liquid fills the tube or the bubbles calm down.

(4) Whether the front and rear straight pipe sections of the flowmeter are guaranteed to be ≥10DN and ≥5DN, and whether the installation position meets the installation requirements (horizontal installation of the flowmeter should be installed at a low position, and vertical installation should be in the bottom and top out).

(5) The transmitter circuit board is a plug-in structure. Due to the large vibration of the field measurement pipeline or liquid, the power board of the flowmeter often becomes loose. If it is loose, disassemble the flowmeter and fix the circuit board again.

(6) Whether the meter body is well grounded.

3.the flow measurement value does not match the actual value

1. Reason analysis

This type of failure is generally caused by the following conditions: (1) Whether the transmitter circuit board is intact;

(2) When the liquid flow rate is too low, the measured liquid contains tiny bubbles, and the bubbles rise and accumulate above the pipe gradually, and the liquid circulation area changes. When there is too much gas, interference signals will be generated, which will affect the accuracy of the measurement;

(3) The signal cable is not properly connected or the insulation performance of the cable decreases during use, causing inaccurate measurement;

(4) The parameter setting value of the converter is not accurate.

2. Solution

(1) Check whether the transmitter circuit board is intact. If the junction box enters water or is corroded by the corrosive test liquid, it may cause the performance of the electrical appliance to decrease or damage. The circuit board should be replaced at this time.

(2) Ensure that the flow rate of the liquid to be measured in the pipeline is above the minimum flow limit value, so that the transmitter can work normally.

(3) Check whether the signal cable connection and the insulation performance of the cable are intact. If the signal cable is loose, just reconnect it; if the insulation of the cable is checked that the insulation does not meet the insulation requirements, a new cable needs to be replaced.

(4) Re-set the converter setting value, and check the converter's zero point and full scale value.

4. the output signal exceeds the full range

1. Reason analysis

(1) The signal cable connection is wrong or the cable connection is disconnected;

(2) The parameter setting of the converter is incorrect;

(3) The converter and sensor model do not match.

2. Solution

(1) Check whether the signal circuit is connected normally or not. If the signal circuit is disconnected, the output signal will exceed the full scale value. At this time, the signal cable must be correctly connected again. At the same time, check whether the insulation performance of the cable is intact. If it does not meet the requirements, it needs to be replaced with a new one.

(2) Check in detail whether each parameter setting and zero point and full scale of the converter meet the requirements.

(3) It is checked that the model of the converter and the sensor are not matched, you need to contact the factory for replacement. To

5. the zero point is unstable

1. Reason analysis

(1) The pipe is not filled with liquid or the liquid contains air bubbles.

(2) Subjectively, it is considered that the tube pump liquid has no flow but actually there is a tiny flow.

(3) Causes of liquid (such as poor conductivity of the liquid, electrode contamination, etc.).

(4) The insulation of the signal circuit has dropped.

2. Solution

(1) The pipeline is not filled with liquid or the liquid contains bubbles are all the reasons for the process. At this time, the process personnel should be asked for confirmation. After the process is normal, the output value can return to normal.

(2) There is a slight flow in the pipe, this is not a malfunction of the electromagnetic flowmeter.

(3) If impurities are deposited on the inner wall of the measuring tube or scale on the inner wall of the measuring tube, or the electrode is contaminated, there may be a zero change, which must be cleaned at this time; if the zero change is not large, you can also try to reset the zero.

(4) Due to environmental conditions, dust, oil, etc. may enter the case of the meter. Therefore, it is necessary to check whether the insulation of the electrode part has dropped or damaged. If it does not meet the insulation requirements, it must be cleaned.

6.air traffic alarm (FGP)

1. The pipe is not full or the liquid contains air bubbles;

2. Measure whether the medium is conductive;

7. excitation alarm (SYS)

1. Whether the excitation wiring EX1 and EX2 are open;

2. Is the total resistance of the sensor excitation coil smaller than 150Ω;

3. If the first two items are normal, the converter is faulty.