Methods for Verifying Electromagnetic Flow Meter Equipment

When people buy electromagnetic flowmeters , it is almost impossible to dismantle and transport them to the National Metrology and Testing Center for calibration because the electromagnetic flowmeter must be used online continuously. Therefore, it is very important to verify the accuracy of large-caliber electromagnetic flowmeters used on site.

So how do people verify the electromagnetic flowmeter equipment when they buy it? Jiangsu Haotian Technology Development Co., Ltd. believes that the best way is to fully verify the accuracy of the electromagnetic flowmeter to determine the accuracy of the electromagnetic flowmeter during application, ensure that the measurement data is authentic and reliable, or whether to replace the electromagnetic flowmeter.

Visual inspection and instrumentation can be used to check whether the sensor's excitation coil resistance, insulation resistance between signal lines, grounding resistance and other items meet the factory standards, and whether the electromagnetic flowmeter converter zero point and output current meet the accuracy requirements. The specific detection methods are:

1. Measure the resistance of the excitation coil to determine whether there is a short circuit between turns of the excitation coil (measure the resistance between line numbers 7 and 8). The resistance 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 indirectly evaluated to be unchanged.

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

3. Measure the contact resistance between the electrode and the liquid (measurement line numbers 1 and 2 and 1 and 3) to indirectly evaluate the general surface conditions of the electrode and lining layer. For example, whether there is a sedimentary layer attached to the electrode surface and the lining layer, and whether the sedimentary layer is conductive or insulating. The resistance value between them should be between 1 kilo-ohm and 1 megohm, 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 it is full of liquid and there is no liquid flowing. Make appropriate adjustments as needed.

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

6. Use the GS8 calibration instrument to test the output current of the converter. When zero flow is given, the output current should be: 4.00mA; when 100% flow is given, 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 values ​​of the excitation current should be within the specified range, approximately 137 (5%) mA.

Evaluate the impact of the external environment on the electromagnetic flowmeter, such as the excitation line and signal line are laid in the same pipeline, the excitation line and signal line are parallel to the high-voltage cable, and there are large transformers or motors around. This evaluation mainly uses visual inspection to observe whether the electromagnetic flowmeter in operation has sudden changes or fluctuations, and roughly judge whether the electromagnetic flowmeter is interfered by electromagnetic waves or other stray waves or whether there are bubbles in the pipeline.