Electromagnetic flowmeter is widely applied in process industries and utilities, measuring instrument must be controlled in a state of operation as required and regular check, inspection method of flow meter
flow value usually has two kinds of offline and online inspection, because of the two methods are flawed, and in the practice of the masses of users to explore the indirect inspection method, some on site validation or evaluate electromagnetic flowmeter calibration flow measurement value is more than the original grade range, provide the basis for continue to use or need further examination.
The present situation of the online inspection it is lack of overall understanding of the electromagnetic flowmeter online check, only see a few Japanese companies published in recent years, the implementation of the real flow online inspection report;
In addition, a few years ago in Shanghai, has begun to explore and develop & other;
Online inspection method & throughout;
And so on.
Chemical industry electromagnetic flowmeter applied in the chemical industry is given priority to with flow control, the flow in the majority with acid, alkaline liquid and slurry, corrosive and abrasion resistance.
Electromagnetic flowmeter failure and failure in practical application, more is due to corrosion leakage, insulation falling, electrode contamination or adherent foreign bodies, etc.
Check the regular maintenance of the traditional electromagnetic flowmeter is a flow sensor pipeline cleaning and inspection, and then implement calibration flow, to reduce the flow sensor from the pipe unloading damage on lining, first on line measuring insulation resistance infer presence of abnormal phenomena, such as to determine whether the next step is to unload pipeline inspection or actual flow calibration.
Mitsubishi chemical (
Three kinds of proportion is: (check way
For online inspection only accounted for 35%;
Unload the pipeline for examination after hydraulic parts cleaning (22%);
Offline for solid flow calibration accounted for 43%.
The water industry (
Tokyo waterway bureau Tokyo waterway bureau of electromagnetic flowmeter to do a comprehensive inspection every year, check the content as follows: appearance inspection, the converter characteristic test, measurement calibration, measurement of each voltage, measure the insulation resistance, confirm the circuit.
Checking and adjusting the instrument because of zero drift, adjust the zero point is very important, and & other;
Online zero & throughout;
Must make stops flowing measured medium, but not easy to do.
So can only be omitted at the scene contains a check of the operation of the sensor is only implemented converter calibration.
Compare the results with historical data, determine the instrument is to continue to use, repair, or update.
The excitation coil sensor according to the measured insulation resistance degradation decided to update or not,
Shanghai tap water company since the 1990 s and raw water company, water company in Shanghai and raw water companies have begun to grope for online inspection and verification method of anomaly.
No stop service may check the flow sensor and converter respectively, and the pipeline with analog signals and other common instrument testing converter, with high degree of calibration (
Depending on the analog signal degrees)
Its method and offline check the same.
Fluid resistance sensor examination is to test the electrode, including check the excitation coil excitation connecting cable and copper resistance, insulation resistance and check, the excitation current converter output check the indirect methods, such as magnetic field intensity.
Have stop line of existing conditions, but also from the preset near the sensor into the hole, check the electric level and lining/sedimentary conditions and cleaning.
Three on-site inspection content site check electromagnetic flowmeter online content, as shown in table 1.
In addition to the zero check, all is the flow sensor, converter and connecting cable 3 separately from the part 1.
The whole machine zero check (
Serial number 1)
This inspection request flow sensor measuring tube filled with liquid and no flow, but it can't do it at the scene of the many.
Do not have conditions can only give up zero check and adjustment of the machine, and only to the converter for separate zero check and adjustment.
Must check is completed in the sensor, and to ensure that the sensor excitation circuit and signal circuit insulation resistance is normal,
All include cable)
Under the premise of to be meaningful, otherwise the machine cannot run normally.
Converter zero negative alone, usually numerical also is very small, if the value is greater than 5% of full scale, will need to do first check, wait for after confirm the reason to be adjusted again.
Electromagnetic flowmeter zero and converter of the machine normally separate zero difference value is less than 1%.
More than 5% of zero there are many cases the user in the pipeline valve closed bad cases caused by incorrect zero.
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