Five aspects of special inspection of electromagnetic flow meter

Abstract: The five aspects of the special inspection of electromagnetic flowmeters are provided by excellent flowmeter and flowmeter manufacturers. 1. Electrode contact resistance measurement Measuring the electrode contact resistance value can indirectly estimate the general condition of the electrode and the lining surface without removing the flow sensor from the pipeline, which is helpful to analyze the cause of the failure. This is especially useful for the inspection of large-diameter electromagnetic flow juice. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following are the details of the five major aspects of the special inspection of electromagnetic flowmeters. 1. Electrode contact resistance measurement Measuring the electrode contact resistance value can indirectly estimate the general condition of the surface of the electrode and the lining layer without removing the flow sensor from the pipeline, which is helpful to analyze the cause of the failure. This is especially convenient for the inspection of large-diameter electromagnetic flow juice. Estimate the inner surface condition of the flow sensor measuring tube, such as whether the electrode and the lining layer have a deposition layer, whether the deposition layer is conductive or insulating, and the contamination of the electrode surface. Compared with the original measurement value, the measured electrode contact resistance value has the following different trends: 1. The resistance value of the two electrodes increases unbalanced (that is, the difference increases); 2. The resistance value increases; 3. The resistance value decreases. These three signs can respectively determine the following possible causes of failure: 1. There is a large decrease in the insulation of an electrode at the electrode of the electromagnetic flow juice; 2. The electrode surface is covered with an insulating layer; 3. The electrode surface and the lining surface are attached with a conductive deposition layer. The above several failure possibilities can also be used as a precursor to predicting failures. Pay attention to the following points when measuring with a multimeter: 1. The resistance value should read the maximum pointer deflection at the moment when the measuring rod touches the terminal, and the measured value should be based on the first measurement. If re-measurement is caused by polarization, the measured values ​​are inconsistent; 2. When measuring the resistance of two electrodes, the polarity of the grounding terminal must be the same, that is, the same measuring rod of the meter is used, the positive rod is connected to the electrode, and the negative rod is grounded . 3. The same type of multimeter and the same range should be used for measurement, and the measurement file of the working range of 1.5V battery is commonly used. 2. The polarization voltage of the electrode Measuring the polarization voltage between the electrode and the liquid will help to judge whether the failure of the zero point instability or the output shaking is caused by the electrode being polluted or covered. Use the 2V DC gear of the digital multimeter to measure the polarization voltage between the two electrodes and the ground respectively (the electromagnetic flow juice can be measured without power failure or without power failure). If the two measurements are nearly equal, the electrode is not contaminated or covered, otherwise the electrode is contaminated or covered. The magnitude of the polarization voltage depends on the“electrode potential”Depending on the properties of the liquid, the measurement may be in the range of a few mV to several hundred mV. Because it is impossible for the two electrodes to be polluted completely and symmetrically during operation, the voltages on the two electrodes form an asymmetric common-mode voltage. The asymmetric common-mode voltage becomes a differential-mode signal, resulting in a zero offset. 3. Measurement of signal cable interference The signal cable is interfered by external electrostatic induction and electromagnetic induction, which will cause the zero point of the electromagnetic flow juice to change. In order to determine whether the zero point change is affected by the interference potential of the signal cable, it is necessary to determine the general range of the interference and the degree of influence on the electromagnetic flowmeter. 4. Determination of whether there is ground potential Electromagnetic flow juice During normal use, if the state of the motor near the sensor changes (such as leakage), the ground potential will change and cause zero point changes. To check whether there is such an influence, short-circuit the working ground C terminal of the converter and the protective ground G terminal, and judge whether there is a ground potential by the change of the zero point (or indicated value). 5. Judging the flow direction of stray current in the pipeline Sometimes it is necessary to find the source of stray interference in the pipeline whether it is upstream or downstream of the flow sensor, so as to narrow the search range and try to reduce or eliminate the interference of stray current. Connect the A and B points of the upstream and downstream jumper wires and grounding wires of the flow sensor electrically insulated from the pipeline to the ammeter respectively. The current measured at point A is 60mAAC, and the current at point B is zero, indicating that the source of interference is upstream of the flow sensor. The electrode contact resistance of the electromagnetic flow juice sensor should be measured and recorded immediately after the newly installed instrument is debugged. After each maintenance, it will be measured once. Analysis and comparison of these data will help to determine the cause of the instrument failure in the future. The resistance value of the electrode in contact with the liquid mainly depends on the surface area of ​​the electrode in contact with the liquid and the conductivity of the liquid to be measured. General structure electrodes in measuring conductivity 5×When the distilled water is 10-6S/cm, the resistance value is 350k～Q, and the conductivity is 150×10-6S/cm domestic and industrial water is about 15kO, conductivity is 1×The brine of 10-2S/cm is about 200n. Use a multimeter to measure the resistance between each electrode terminal and the ground when it is filled with liquid. Experience shows that the difference between the contact resistance values ​​of the two poles should be less than 10%-20%, otherwise it indicates a fault. Measuring electrode contact resistance with a multimeter is not a method to correctly measure the exact value of the resistance, but to determine the general value. An accurate measurement must be done with an AC bridge, such as“Kohlrashh bridge”Wait. The above is the whole content of this article. You are welcome to inquire about the flowmeter selection and quotation of our factory. 'Five Aspects of Special Inspection of Electromagnetic Flow Meters'
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