An electromagnetic flowmeter fault causes. The zero-point instability can be roughly summarized as the cause of the five-sided fault.
They are:
1 Electromagnetic flowmeter sensors are not perfect due to stray currents and other external interference:
Check the flow chart item 3. External interference effects such as pipe stray current etc. Main series of electromagnetic flowmeters have good grounding protection. Usually the grounding resistance is less than 1000. Do not share grounding with other electrical appliances. Sometimes the environmental conditions are better. The series of electromagnetic flowmeters can also work properly without being grounded, but once a good environment does not exist, the instrument will malfunction. Checking it again will cause more trouble.
Changes in the state of the power equipment near the flow sensor (eg, increased leakage current) are caused by a change in ground potential. Electrical causes ZN series electromagnetic flowmeter zero point changes. For inspection methods, see section IX.
2 electromagnetic flowmeter liquids (such as liquid conductivity uniformity, electrode contamination and other issues);
The fourth item in the inspection flow chart. The liquid conductivity changes or is non-uniform. When it is at rest, it will change the zero point and the flow will cause the output to sway. Therefore, the flowmeter should be located far away from the point where the chemical solution is injected or downstream of the chemical reaction section of the pipeline. Well installed upstream of these establishments.
If the liquid contains a solid phase, or impurities deposit on the inner wall of the measuring tube, or on the inner wall of the measuring tube, or the electrode is contaminated by grease, etc., there may be a zero point change because the scale on the inner wall surface and the degree of contamination of the electrode may not be completely. The same and symmetrical, destroy the balance of the initial set-down of the plant. Positive measures to clear the dirt and sediment layer; if the change is not large, you can try to re-zero.
3 electromagnetic flowmeter signal circuit insulation down.
Check the fifth item of the flow chart. The signal circuit insulation decline will form zero instability. The signal circuit insulation degrades due to insufficient earth and caused by the insulation drop of the pole part, but it cannot exclude the signal cable and its terminal insulation is lowered or destroyed. Because sometimes the on-site environment is very harsh, a little carelessly sealed the instrument cover/wire connection is inadvertently filled with moisture acid mist or dust particles intruding into the instrument terminal box or cable protection layer, so that the insulation is lowered. Insulation resistance of the signal circuit is checked According to the two sides of the cable side and the flow sensor side, the test is performed with a megohmmeter. The signal cable is easy to do first. The flow sensor is further divided into two steps: the contact resistance of the electrode is filled with liquid and the measurement after one tube, U Insulation resistance.
4/ Check electrode contact resistance and electrode insulation resistance in 2 steps.
(1) Liquid-filled measuring electrode surface spoon Liquid contact resistance Flow sensor Discharge the signal cable connection, measure the resistance between each electrode and the grounding point with a multimeter, and the left of the two electrodes to the ground should be 10%-20%. Section IX "Measurement of Contact Resistance of One Electrode" will be further explained.
(2) Empty tube measurement electrode Insulation vent tube, with a dry cloth on the inner surface, until completely dry, with H500VDC megohmmeter to measure the resistance between the electrodes and the ground, the resistance must be above 100MΩ..
They are:
1 Electromagnetic flowmeter sensors are not perfect due to stray currents and other external interference:
Check the flow chart item 3. External interference effects such as pipe stray current etc. Main series of electromagnetic flowmeters have good grounding protection. Usually the grounding resistance is less than 1000. Do not share grounding with other electrical appliances. Sometimes the environmental conditions are better. The series of electromagnetic flowmeters can also work properly without being grounded, but once a good environment does not exist, the instrument will malfunction. Checking it again will cause more trouble.
Changes in the state of the power equipment near the flow sensor (eg, increased leakage current) are caused by a change in ground potential. Electrical causes ZN series electromagnetic flowmeter zero point changes. For inspection methods, see section IX.
2 electromagnetic flowmeter liquids (such as liquid conductivity uniformity, electrode contamination and other issues);
The fourth item in the inspection flow chart. The liquid conductivity changes or is non-uniform. When it is at rest, it will change the zero point and the flow will cause the output to sway. Therefore, the flowmeter should be located far away from the point where the chemical solution is injected or downstream of the chemical reaction section of the pipeline. Well installed upstream of these establishments.
If the liquid contains a solid phase, or impurities deposit on the inner wall of the measuring tube, or on the inner wall of the measuring tube, or the electrode is contaminated by grease, etc., there may be a zero point change because the scale on the inner wall surface and the degree of contamination of the electrode may not be completely. The same and symmetrical, destroy the balance of the initial set-down of the plant. Positive measures to clear the dirt and sediment layer; if the change is not large, you can try to re-zero.
3 electromagnetic flowmeter signal circuit insulation down.
Check the fifth item of the flow chart. The signal circuit insulation decline will form zero instability. The signal circuit insulation degrades due to insufficient earth and caused by the insulation drop of the pole part, but it cannot exclude the signal cable and its terminal insulation is lowered or destroyed. Because sometimes the on-site environment is very harsh, a little carelessly sealed the instrument cover/wire connection is inadvertently filled with moisture acid mist or dust particles intruding into the instrument terminal box or cable protection layer, so that the insulation is lowered. Insulation resistance of the signal circuit is checked According to the two sides of the cable side and the flow sensor side, the test is performed with a megohmmeter. The signal cable is easy to do first. The flow sensor is further divided into two steps: the contact resistance of the electrode is filled with liquid and the measurement after one tube, U Insulation resistance.
4/ Check electrode contact resistance and electrode insulation resistance in 2 steps.
(1) Liquid-filled measuring electrode surface spoon Liquid contact resistance Flow sensor Discharge the signal cable connection, measure the resistance between each electrode and the grounding point with a multimeter, and the left of the two electrodes to the ground should be 10%-20%. Section IX "Measurement of Contact Resistance of One Electrode" will be further explained.
(2) Empty tube measurement electrode Insulation vent tube, with a dry cloth on the inner surface, until completely dry, with H500VDC megohmmeter to measure the resistance between the electrodes and the ground, the resistance must be above 100MΩ..
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