The working principle of the plug-in electromagnetic flowmeter is based on Faraday's law of electromagnetic induction. In the electromagnetic flowmeter, the conductive medium in the measuring tube is equivalent to the conductive metal rod in the Faraday test, and the two electromagnetic coils at the upper and lower ends generate a constant magnetic field. When a conductive medium flows, an induced voltage is generated. The two electrodes inside the pipe measure the induced voltage generated. The measuring tube is electromagnetically isolated from the fluid and the measuring electrode by a non-conductive inner liner (rubber, Teflon, etc.).
Accurate measurement needs to choose the correct instrument, the quality of the instrument is the main, and secondly, it is necessary to consider the installation requirements. If the installation is not standardized, the instrument cannot be fully utilized. Therefore, for the installation of the flowmeter, we must pay attention to it. The technicians of Huaheng Instrument will introduce you to the installation requirements and precautions of the plug-in electromagnetic flowmeter:
1. The plug-in electromagnetic flow meter should be kept away from equipment with strong electromagnetic fields;
2. There should be no strong vibration in the installation place, the pipe is fixed firmly, and the ambient temperature does not change much;
3, The installation position must ensure that the pipe is always filled with the measured fluid, the length of the straight pipe on the upstream side of the sensor installation pipe is greater than 8D, and the length of the straight pipe on the downstream side is not less than 5D;
4. Clean the welding slag and burrs of the base of the pipe to be tested;
5. Install the DN80 ball valve on the mounting base, pay attention to the long cavity of the ball valve upward, check that the ball valve switch is normal; install the compression screw seat kit to the ball valve, loosen the positioning screw and the compression nut, insert the sensor into the rod and insert through the ball valve. The pipe being tested. The insertion depth of the sensor is 3mm outside the base. After meeting the requirements, tighten the positioning screw and the compression nut. Also note that the sensor direction mark is consistent with the fluid flow direction.
6. The opening on the pipe to be tested is larger than the base pipe, and the depth of the base pipe inserted into the opening of the pipe to be tested is the flatness of the two sides;
7. The plug-in electromagnetic flowmeter is welded by stainless steel welding rod, and the flange surface is parallel to the tube axis after welding;
8. Connect the power supply and other connections according to the instructions of the plug-in electromagnetic flowmeter. After power-on, check the instrument display to confirm that the pipe under test is full of fluid and the flow rate is zero. ;
9. After the fluid in the pipe under test is flowing and stable, check the instrument display. At this time, turn the sensor direction to maximize the display value, and lock the positioning screw and the compression nut;
10. For the case where the flow variation range is large and the fluid velocity is lower than the minimum flow rate required by the flowmeter for a long time, it should be considered to reduce the process pipeline or use two large and small small parallel flowmeters installed;
11. The plug-in electromagnetic flowmeter should be installed on the vertical process pipe as well as the ordinary electromagnetic flowmeter. This prevents the suspended solid from sinking on the electrode and raises the oil in the fluid to the outside of the measurement range of the electrode. When the flowmeter is installed on the horizontal process pipeline, the electrode of the sensor should be placed on the horizontal axis to avoid the interference of the electrode due to the bubble, resulting in measurement error;
12, Vertical installation, the sensor should be inserted into the pipeline should be less than 5 ° perpendicular to the vertical diameter of the pipeline section, suitable for measuring the cleaning medium with small vibration of the pipeline;
13. Tilt-mounted, the angle between the axis of the sensor and the axis of the pipe to be tested is 45°. It is suitable for measuring the flow of liquid with large diameter and measuring other impurities in the medium. The installation method has small water resistance and should not be entangled.
Fault 1: There is no output current after the power is turned on. Cause: The power is not turned on.
Removal method 1. Check if the fuse is blown 2. Check the power circuit wiring.
Fault 2: The current output is zero (4 mA) after the power is turned on. Cause: 1. The direction of the sensor mark is opposite to the flow of the fluid. 2. The converter excitation power line is connected incorrectly. 3. The input signal lines E1 and E2 are reversed.
Exclusion method: 1. Adjust the direction of the sensor to match the direction of the fluid. 2. Rewire the cable in the correct way. 3. Replace the signal lines E1 and E2.
Fault 3: The output signal exceeds 20mA after power-on or during operation. The flowmeter range is smaller than the actual measurement range.
Elimination method to reset the flowmeter range to make it reasonable
Fault 4: The output signal fluctuates too much. Cause: 1. There is gas at the sensor electrode, which causes the electrode to be in poor contact with the measured medium. 2. There is accumulation on the surface of the electrode, and the electrode is in poor contact with the medium. 3. The media flow actually fluctuates greatly. 4. Poor grounding.
Discharge method: 1. Correct installation to eliminate the influence of gas in the pipeline. 2. Clean the electrode surface. 3. Increase the meter damping time.
Fault 5: The output signal is gradually reduced or zero during operation. Cause: 1. The sensor is flooded. 2. The signal line is poorly insulated. 3. There is accumulation on the surface of the electrode, and the ability of the electrode to pick up the signal is reduced.
Discharge method: 1. Exclude water, replace signal line 3, clean electrode 4, and improve grounding method.