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The inspection content of electromagnetic flowmeter

Date:2019-11-27 source:

The electromagnetic flowmeter is mainly used in industrial production by flow monitoring.In specific application, the common faults of electromagnetic flowmeter are mainly caused by erosion leakage, lower insulation layer, electrical contamination or adhesion of dirty things.The objective of routine inspection of the electromagnetic flowmeter is to ensure or verify that the electromagnetic flowmeter is operating under a control plan.

The inspection content of electromagnetic flowmeter

At ordinary times, there are two kinds of inspection methods: free online inspection and offline inspection. The key is to verify whether the total flow measurement value of electromagnetic flowmeter conforms to and maintain the estimated metrological verification regulation.The key inspection contents are: check the electromagnetic flowmeter, in addition to the zero check, but also the flow sensor, converter and connection cable separation.

Connection cable inspection

This inspection is to check the conduction and insulation resistance of each core of the power line and the excitation regulator line, and check whether the grounding device of each shielding layer is intact.

Ii. Converter inspection

The content of this inspection is to show the total flow data signal to carry out zeroing and correction by replacing the controller with the digital signal device that conforms to the model and specification of the universal instrument panel and its steam flowmeter.Calibration includes zero check and adjustment, preset check, excitation current measurement, current/frequency output check, etc.It must be noted that the inspection of new items should be compared with the last inspection value (or the original factory value) to analyze whether there is a change or whether the change is in accordance with the original metrological verification provisions.

Three, the whole equipment zero point inspection

The technical standard for the zero-point inspection of the whole equipment is that the flow sensor measuring tube is filled with liquid and has no fluidity, which is not necessary in many companies on the spot and the zero-point inspection and adjustment of the whole equipment can be abandoned, but the converter can then be independently zero-point inspection and adjustment.Technically speaking, this must have practical significance after the controller inspection and ensure that the insulation resistance of the controller excitation regulator control loop and data signal control loop is all right (including the cable), otherwise the whole equipment can not work properly.In general, the independent zero of the converter is negative, and the standard value is not large.If its ** value exceeds 5% of the full range, it must be checked first and adjusted after the cause is determined.Generally speaking, the difference between the zero point of the whole equipment and the independent zero point of the converter is less than 1%.The zero point difference of more than 5% is caused by a number of cases in which the customer missets the zero when the valve is not closed properly.

Iv. Flow sensor inspection

The inspection content is: according to the inspection of the excitation regulator's electromagnetic coil and check the excitation current measured by the converter to simply evaluate whether the magnetic induction intensity is changing;The electrical grade liquid resistor was measured to evaluate the surface contamination and lining adhesion of the electrical grade resistor.Check the insulation resistance at each position to distinguish the level of deterioration of the part to assess whether it will lead to dry torsion.For pipes that can terminate material mobility standards, the thickness of the electrical grade and lining adhesion layer can be checked and measured to estimate the change in the total flow value before and after clearing the adhesion layer due to the change in the total area of liquidity.

(1) measure the copper resistor of the electromagnetic coil of the excitation regulator

Measure the coil resistance with a height digital multimeter or a wheaton bridge, and adjust the temperature index when necessary to compare with the values of the instrument panel files.Determine whether the electromagnetic coil is on - off excellent and non - turn - to - turn short circuit fault.

(2) check the insulation resistance of the electromagnetic coil of the excitation regulator

Excitation regulator solenoid coil and terminal row insulation layer of excitation regulator control circuit to reduce after get damp, very will put the excitation regulator data signals into traffic data transmission power circuit, the electric level plus a lot of insulation resistance and data signals resistor of excitation regulator working voltage bleeder circuit, produce a lot of common mode interference signal data.When this electromagnetic interference exceeds the ability of the converter's preamplifier to suppress the operation, the zero point of the converter will drift.When the insulation resistance reduction is not very serious, it is not easy to detect the condition in the operation of the instrument panel.Besides IP68 no row terminal box, practice because of carelessness, terminal box without sealing in moisture, reduce insulation resistance to the terminal 5 ~ 6 m Ω following the most easily lead to common faults.Dry the terminal, common faults can be removed.

(3) check the electric-level liquid resistor

The electrical level of the flow sensor should be measured immediately after the adjustment of the instrument panel and processed.After each maintenance measurement, the analysis of this kind of database is more conducive to distinguish the cause of common dashboard faults.

The contact resistance between the electrical level and the liquid depends on the conductivity of the liquid to be measured on the contact surface.The resistance values of different substances were significantly different.Electrical stage liquid resistor a pointer multimeter can be used to measure the resistor between each stage terminal and the ground when the measuring tube is filled with liquid.Work experience shows that the difference between the contact resistance values of the two electrical levels measured respectively should be less than 10% ~ 20%, otherwise there are common faults.

If there is any difference between the measured liquid resistor and the original measured value, the reasons are as follows: a, the covering of adhesive layer of dielectric strength of two electric stages is inconsistent or the insulation resistance of control loop of data signal of one electric stage is reduced;B. When the resistance value is increased, the electrical surface is covered by cable sheath;C. The decrease of resistance value refers to the decrease of conductive alluvium adhered to the surface of the surrounding lining of the electrical grade or the decrease of the insulation layer of the electrical grade assembly line (such as the insulation ring).Sometimes, although there are no common faults, effective countermeasures should be taken as a sign of common faults.

(4) measure the working voltage of electric polarization between electric stage and liquid

Measuring this operating voltage will help to determine whether the electrical level is obscured or obscured, which will result in the common failure of zero point instability or output shaking.

(5) check the insulation layer between the data signal power supply circuit and the excitation circuit/data signal power supply circuit

This inspection is to assess whether the insulation layer is lowered into the dry torsion.When checking the data signal power supply circuit, the power cord should be temporarily released with the power level.Causes the insulation layer to reduce the cause of wiring terminals not sealed into the moisture, safety protection type controller cable sawed again when the continuation of the waterproof solution.

(6) check electrical insulation resistance and lining

In this inspection, the caliber instrument panel should be removed from the pipe, while the large-size instrument panel can be emptied after its own effusion into the pipe.If the lining has adhesive layer, it shall be eliminated and the cleaning cycle time shall be defined according to the thickness of the stacking layer.If the adhesive layer is not thick and the conductivity is the same as that of the liquid, the total area transformation extra deviation can be ignored.If the conductivity of the adhesive layer is lower than that of the liquid, it will cause an extra deviation in the direction of the adhesive layer.

At present, Shanghai porcelain flowmeter has been exported to more than 100 countries, involved in more than 100 industries.At the same time, the research and development of micro flowmeter also obtained the metrological certification.At home to fill the gap in the micro flowmeter, while breaking the monopoly of foreign enterprises.

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