测量原理是法拉第电磁感应定律，传感器主要组成部分是：测量管、电极、励磁线圈、铁芯与磁轭壳体。 The measuring principle of HN LD series electromagnetic flowmeter is Faraday's law of electromagnetic induction. The main components of the sensor are: measuring tube, electrode, excitation coil, iron core and yoke housing. The electromagnetic flowmeter is mainly used to measure the volume flow in conductive liquids and slurries in closed pipes. Including strong corrosive liquids such as acid, alkali and salt. Electromagnetic flowmeters are widely used in petroleum, chemical, metallurgy, textile, food, pharmaceutical, papermaking and other industries, as well as in environmental protection, municipal management, and water conservancy construction.
1: The electromagnetic flow transmitter should be installed in a dry and ventilated place indoors. Avoid installing in places where the ambient temperature is too high, should not be subject to strong vibration, and try to avoid equipment with strong magnetic fields, such as large motors, transformers, etc. Avoid installing in places with corrosive gas. Installation location is convenient for maintenance. This is the environmental condition to ensure the normal operation of the transmitter. 2: In order to ensure that the measuring tube of the electromagnetic flow transmitter is filled with the measured medium, it is best to install the changer vertically and flow from bottom to top. Especially for liquid-solid two-phase flow, it must be installed vertically. If only horizontal installation is allowed on site, it must be ensured that the two electrodes are at the same level 3: Valves and bypasses should be installed at both ends of the electromagnetic flow transmitter. 4: The millivolt AC potential measured by the electrodes of the electromagnetic flow transmitter is based on the liquid potential in the transmitter. In order to stabilize the liquid potential and to maintain the equipotential between the transmitter and the fluid to ensure stable measurement, the transmitter housing and the metal tube should be well grounded at both ends, and the converter housing should also be grounded. The grounding resistance cannot be greater than 10 and cannot be shared with the grounding wire of other electrical equipment. If it is not possible to ensure good contact between the transmitter housing and the metal pipe, connect them with metal wires. Reliable grounding. 5: In order to avoid interference signals, the signal between the transmitter and the converter must be transmitted with a shielded wire. Signal cables and power cables are not allowed to be placed in the same cable steel tube in parallel. The length of the signal cable should not exceed 30m. 6: The installation site of the converter should avoid strong AC and DC magnetic fields and vibrations. The ambient temperature is -20 to 50 ° C. It does not contain corrosive gases and the relative humidity is not more than 80%. 7: In order to avoid the influence of relative measurement of flow rate, the flow regulating valve should be set downstream of the transmitter. For the small-diameter transmitter, because the distance from the center of the electrode to the inlet of the flowmeter is equivalent to several times the diameter D, the upstream straight pipe may not be specified. But for larger caliber flowmeters, generally there should be more than 5D straight pipe section in the upstream, and generally no straight pipe section is required in the downstream.
必须是在线连续使用，几乎不可能拆除再运输到国家计量检测中心进行检定。 Because the electromagnetic flowmeter must be used continuously online, it is almost impossible to dismantle and transport it to the National Metrology and Testing Center for verification. Therefore, it is necessary to verify the accuracy of the large-diameter electromagnetic flowmeter used in the field. Accuracy verification of electromagnetic flowmeters It is also very useful for the management of electromagnetic flowmeters to ensure their accuracy and reliability, accumulate original comparison data, and conduct future verification and verification. The accuracy of the electromagnetic flowmeter can be verified by the volume of the clear water tank and the electromagnetic flowmeter. Evaluate the impact of the external environment of the electromagnetic flowmeter, such as laying the same line as the excitation line and signal line, paralleling the excitation line and signal line with high-voltage cables, and surrounding large transformers or motors. This evaluation mainly uses the visual inspection method to observe whether the electromagnetic flowmeter is abrupt or fluctuating during operation to roughly judge whether the electromagnetic flowmeter is interfered 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 multimeter, one 500V megohmmeter, one pointer multimeter and commonly used tools. 2. Validation of clear water tank volume method: The verification of the measurement accuracy of the electromagnetic water flowmeter delivered by the water factory adopts the clear water tank volume method, which is one of the methods often used by water supply enterprises. Under the condition that the geometric size of the clear water tank is measured accurately and the operation errors are reduced, a higher comparison reference effect can be obtained. The principle of the clear water tank volume method is: use high-precision steel ruler to measure the actual space plane size of the clear water tank and the suction well, and accurately calculate the actual planar area of the clear water tank and the suction well. First set the clear water level to a higher level and close all water outlet valves. After the water level of the clear water tank is stable, use the clear water level transmitter and manually measure the water level of the clear water tank and suction well with high precision steel ruler. In order to correct the error caused by the leakage of valves such as the clear water tank, the water level of the clear water tank and the suction well is measured again after a certain period of time, and the water leakage per unit time is calculated in order to correct the water measurement and reduce the error. Record the accumulated flow of the electromagnetic flowmeter to be verified. The purpose of manually measuring the level of the clear water tank and the suction well is to verify the accuracy of the level transmitter. Then turn on the water pump and 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 tank is stable, the clear water tank and suction wells are manually measured with a high-precision steel ruler, and the water level of the clear water pool and the suction well is recorded again, and the cumulative flow of the electromagnetic flowmeter to be verified is recorded. . Finally, the water level difference ⊿h between the clear water tank and the suction well is calculated, so as to calculate the actual water volume of the clear water tank and the suction well. The actual water amount is equal to the height difference ⊿h times the plane area and the corrected water volume. 的计量系统精度。 Then calculate the water volume of the electromagnetic flowmeter to be verified, subtract the accumulated volume of the electromagnetic flowmeter from the actual water volume of the clear water tank, and get the error between them, so as to verify the accuracy of the metering system of the factory water electromagnetic flowmeter . The clear water volume method is used to verify the measurement accuracy of the electromagnetic water flowmeter of the factory water and the factory water when the state of the water tank is completely static, so the data obtained is more accurate. Calculated as follows:
E = (Q standard—Q instrument) / Q standard × 100%
Where: E is the error value between the two;
Q is the volume calculated by the difference in the height of the clear water tank;
Q meter is the flow value accumulated by the flowmeter during verification.