How to verify the accuracy of electromagnetic flowmeter?

The verification of the accuracy of the electromagnetic flowmeter is very useful for the management of the electromagnetic flowmeter, ensuring its accuracy and reliability, and accumulating the original comparison data. It is also very useful to perform verification and verification in the future. The verification of the accuracy of the electromagnetic flowmeter can use the clear water tank volume and electromagnetic flowmeter calibration equipment.

Fully verify the accuracy of the electromagnetic flowmeter to determine the accuracy of the electromagnetic flowmeter in the application process of the waterworks and ensure that the measurement data is authentic and authentic or replace the electromagnetic flowmeter.

Visual inspection and instrumentation methods are used to check whether the excitation coil resistance of the sensor, the insulation resistance between the signal lines, and the grounding resistance are in compliance with the pre-factory standards. Does the zero point of the electromagnetic flowmeter converter and the output current meet the accuracy requirements? . The specific detection method is:

1. Measure the resistance value of the excitation coil. Determine if there is a short circuit between the excitation coils (resistance value between line number 7 and 8). 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 indirect evaluation of the electromagnetic field sensor sensor's magnetic field strength does not change.

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

3. Measure the electrode-to-liquid contact resistance (line numbers 1 and 2 and 1 and 3) to indirectly assess the general condition of the electrode and liner surface. If the electrode surface and the liner layer adhere to the deposited layer, the deposited layer is conductive or insulating. The resistance between them should be between 1 kilohms and 1 megohms, and the resistance values ​​of 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 electromagnetic flowmeter 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 of the signal cable and the excitation cable and check that the shielding is intact.

6. Use the GS8 calibration instrument to test the converter's output current. When given zero flow, the output current should be: 4.00mA; when given 100% flow, the output current should be: 20.00mA. The error of the output current value should be better than 1.5%.

7. Test the excitation current value (between converter terminals 7 and 8). The positive and negative field current values ​​should be in the specified range, approximately 137 (5%) mA.

Evaluate the influence of the external environment of the electromagnetic flowmeter on the impact of the electromagnetic flowmeter's operation accuracy, such as the laying of the same line of the excitation line and the signal line, the excitation line and the signal line and the high voltage cable, and the surrounding large transformers or motors. This evaluation mainly uses the visual inspection method to observe whether the electromagnetic flowmeter in operation is in a state of abrupt change or fluctuation. It is roughly judged whether the electromagnetic flowmeter is disturbed by electromagnetic waves or other stray waves or whether there are bubbles in the pipeline.

The instruments and tools required for the verification of the electromagnetic flowmeter itself: one GS8, one 4-1/2 multimeter, one 500V megohmmeter, one analog multimeter, and common tools.

Clear water pool method verification:

The water tank factory water electromagnetic flowmeter measurement accuracy verification using the clear water tank volume method is one of the methods commonly used by water companies.

In the condition of measuring the geometrical dimension of the clear water tank and reducing the error of each operation, a higher reference effect of comparison can be obtained.

The principle of the clear water tank volume method is: using a high-precision steel ruler to measure the actual space plane size of the clear water tank and the water absorption well, and accurately calculate the actual plane area of ​​the clear water tank and the water absorption well. First adjust the water level in the clear water tank to a higher water level and close all the outlet valves.

After the water level of the pool is stable, the water level of the clear water tank and the water absorption well is accurately measured by a clear tank liquid level transmitter and a high-precision steel ruler. In order to correct the error caused by the valve leakage of the clear water tank, the clear water tank and the water level of the water absorption well are measured again after a certain time interval, and the water leakage per unit time is calculated to correct the water discharge measurement and reduce the error. Record the electromagnetic flowmeter accumulative flow to be verified, and the purpose of manually measuring the liquid level of the clear water tank and the water absorption well is 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 in the pool is stable, use the clear water tank level transmitter again and use a high-precision steel rule to manually measure the water level of the clear water tank and the water absorption well, record the water level of the clear water tank and the water absorption well again, and record the accumulated flow of the electromagnetic flowmeter to be verified. . Finally, the height difference ⊿h of the clear water tank and the water absorption well is calculated to calculate the actual water volume of the clear water tank and the water absorption well. The actual water amount is equal to the height difference ⊿h multiplied by the plane area and the corrected water amount.

Then calculate the amount of water to be verified by the electromagnetic flowmeter, and use the actual water volume of the clear water tank minus the accumulated amount of the electromagnetic flowmeter to obtain the error between them, so as to verify the accuracy of the metering system of the manufactured water electromagnetic flowmeter. Using the clear water tank volumetric method to verify the metering accuracy of the factory water water electromagnetic flowmeter needs to be performed in a completely static state in the clear water tank state, so that the obtained data is more accurate. Calculated as follows:

E=(Q standard Q meter)/Q standard 100%

In the formula: E is the error value between the two;

Q is marked as the volume calculated by the difference in the falling height of the clear water tank;

The Q meter is the flow rate value that the flow meter accumulates during verification.