Electromagnetic flowmeter accuracy verification method - Database & Sql Blog Articles

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Accuracy Verification of Electromagnetic Flowmeters For the management of electromagnetic flowmeters, to ensure their accuracy and reliability, it is also very useful to accumulate the original comparison data for future verification and verification. The accuracy verification of the electromagnetic flowmeter can utilize the clearing tank volume and electromagnetic flowmeter calibration equipment.

Comprehensive verification of the accuracy of the electromagnetic flowmeter to determine the accuracy of the electromagnetic flowmeter in the application process of the water plant, to ensure that the measurement data is authentic or whether to replace the electromagnetic flowmeter.

1. Using visual inspection and instrumentation method, use GS8 to check whether the resistance coil value of the sensor, the insulation resistance between the signal lines, the grounding resistance and other items meet the pre-factory standards, and whether the zero point and output current of the electromagnetic flowmeter converter are satisfied. Precision requirements. The specific detection method is:

(1) Measure the resistance value of the excitation coil to determine whether the excitation coil has a turn-to-turn short circuit (resistance between the line numbers “7” and “8”), and the resistance value should be between 30 ohms and 170 ohms. If the resistance is the same as the factory record, the coil is considered to be good, and the magnetic field strength of the electromagnetic flowmeter sensor is not indirectly evaluated.

(2) Measure the insulation resistance of the excitation coil to ground (measurement number "1" and "7" or "8") to determine whether the sensor is damp, and the resistance value should be greater than 20 megohms.

(3) Measure the contact resistance between the electrode and the liquid (measurement numbers "1" and "2" and "1" and "3"), and indirectly evaluate the general condition of the surface of the electrode and the lining layer. If the electrode surface and the backing layer are attached to the deposited layer, whether the deposited layer is electrically conductive or insulative. The resistance between them should be between 1 kohm and 1 megohm, and the resistance values ​​of the line numbers "1" and "2" and "1" and "3" should be roughly symmetrical.

(4) Close the valve on the pipeline and check the zero point of the whole machine when the electromagnetic flowmeter is full of liquid and the liquid is not flowing. Make appropriate adjustments as appropriate.

(5) Check the insulation resistance of each core wire of the signal cable and the excitation cable to check whether the shielding layer is intact.

(6) Test the output current of the converter using the GS8 calibration instrument. When zero flow is given, the output current should be: 4.00 mA; when given 100% flow, the output current should be: 20.00 mA. The error of the output current value should be better than 1.5%.

(7) Test the excitation current value (between the converter terminals "7" and "8"), the positive and negative excitation current should be within the specified range, which is approximately 137 (5%) mA.

Evaluate the influence of the external environment of the electromagnetic flowmeter, such as the same pipeline laying of the excitation line and the signal line, the excitation line and the signal line are parallel with the high voltage cable, and there are large transformers or motors around to evaluate the influence of the electromagnetic flowmeter on the running accuracy. This evaluation mainly uses visual inspection to observe whether the electromagnetic flowmeter in operation has sudden or fluctuating conditions. It is generally judged whether the electromagnetic flowmeter is disturbed by electromagnetic waves or other stray waves or whether there are air bubbles in the pipeline.

The instruments and tools required for the verification of the electromagnetic flowmeter itself: one GS8, one 4-1/2 million meter, one 500V megohm meter, one pointer type multimeter and common tools.

2. Clear water volume method verification:

The verification of the measurement accuracy of the water meter of the water mill is based on the volumetric method of the clear water pool, which is one of the methods frequently used by water supply enterprises.

Under the condition that the geometrical dimensions of the clear water pool are accurately measured and the operation errors are reduced, a higher reference effect can be obtained. The principle of the clearing water volume method is to measure the actual spatial plane size of the clear water tank and the water absorbing well by using a high-precision steel ruler, and accurately calculate the actual plane area of ​​the clear water tank and the water absorbing well. First adjust the water level of the clear water tank to a higher water level and close all the water outlet valves.

After the water level of the clear water pool is stable, the clear water level transmitter is used and the water level of the clear water tank and the water absorption well is accurately measured by a high-precision steel ruler. In order to correct the error caused by the leakage of the valve such as the clear water tank, the water level of the clear water tank and the water absorption well are measured again after a certain time interval, and the water leakage amount per unit time is calculated to correct the water metering and reduce the error. Record the cumulative flow rate of the electromagnetic flowmeter to be verified, and manually measure the liquid level of the clear water tank and the water absorption well to verify the accuracy of the liquid level transmitter. Then turn on the water pump and open the water outlet valve. After a certain period of time, close the water outlet valve to stop the water pump.

After the water level of the clear water pool is stable, the water level transmitter of the clear water pool is used again and the water level of the clear water tank and the water absorption well is accurately measured by a high-precision steel ruler. The water level of the clear water tank and the water absorption well is recorded again, and the cumulative flow rate of the electromagnetic flowmeter to be verified is recorded. . Finally, calculate the water level difference ⊿h between the clear water tank and the water absorbing well, and calculate the actual water volume of the clear water tank and the water absorbing well. The actual water quantity is equal to the height difference ⊿h multiplied by the plane area and the corrected water volume.

Then calculate the water quantity of the electromagnetic flowmeter to be verified, and subtract the cumulative amount of the electromagnetic flowmeter from the actual water volume of the clear water pool to obtain the error between them, thereby verifying the accuracy of the metering system of the factory water electromagnetic flowmeter. The clearing volume method is used to verify the measurement accuracy of the factory water electromagnetic flowmeter. The data in the clear water pool is completely static, so the data obtained is more accurate. Calculated as follows:

E=(Q mark—Q meter)/Q mark×100%

Where: E is the error value between the two;
Q is the volume calculated from the difference in the height difference of the clear water pool;
The Q meter is the flow rate value accumulated by the flow meter during verification.