Industry new

Application description of electromagnetic flowmeter in the original pump station

1 Introduction

In recent years, with the continuous improvement of the automation technology level of domestic water supply industry and the requirements of trade settlement measurement, electromagnetic flowmeters have been more and more widely used and promoted, especially in the water supply industry of China, MMG/KL-GB electromagnetic flowmeter. The application has been widely recognized.

2 Basic principles

According to Faraday's law of electromagnetic induction, when a conductive liquid cuts magnetic lines of force in a magnetic field, an induced potential is generated in the conductor, and the magnitude of the induced potential is proportional to factors such as the magnetic induction intensity and the strength of the magnetic field of the cutting force.

The potential is given by:

E=K×B×V×D

Where: E - induced voltage;

K——meter constant;

B——magnetic induction strength;

V - average flow rate;

D——Measure the inner diameter of the tube.

When a fluid is flowing, the fluid flows through a magnetic field perpendicular to the flow direction, and the flow of the conductive liquid induces a voltage proportional to the average flow rate or the flow rate per unit volume, so that the induced voltage has a minimum conductivity as long as the measured fluid has a minimum conductivity. The signal is detected by two electrodes in direct contact with the liquid and transmitted through the cable to the amplifier, which is then converted into a uniform output signal.

3 Main technical features and installation requirements

3.1 Main technical characteristics of electromagnetic flowmeter

1 Since the measurement results are independent of physical parameters such as pressure, temperature, and conductivity of the liquid, the measurement accuracy is high and the operation is reliable.

2 There is no obstruction in the measuring tube, so there is no additional pressure loss, ie no additional head loss for tap water measurement.

3 Only the pipe and the electrode are in contact with the liquid to be tested. Therefore, as long as the electrode material is properly selected, corrosion resistance and wear resistance can be achieved. It has the characteristics of long service life and low maintenance requirements.

4 The flow rate of the fluid in the forward and reverse directions can be measured.

5 The output signal mode is flexible. There are pulses, currents, frequencies, etc.

3.2 Electromagnetic flowmeter use and installation requirements

1 The upstream pipe of the electromagnetic flowmeter has at least 5 pipe lengths of straight pipe sections, and at least 3 pipe lengths of straight pipe sections downstream. When conditions permit, the length of the straight pipe before the flowmeter is relaxed is 10 times or more.

2 In the installation of the electromagnetic flowmeter, the sensor grounding ring should be grounded reliably, and the grounding resistance should be no more than 10 OΩ.

3 Be careful to avoid external electromagnetic interference in the choice of the use environment, especially to avoid interference from power frequency electromagnetic fields.

4 For the installation of the valve in the upstream pipeline of the flowmeter outside the front distance, especially the butterfly valve or the right angle bend pipe, etc., it is better to install the rectifier in the straight pipe of 5-10 times the diameter of the upstream of the flowmeter. Achieve stable flow patterns and improve metering accuracy.

4 Electromagnetic flow and installation and configuration in the water supply industry

Based on the measurement principle and measurement characteristics of electromagnetic flowmeter, it has become a widely used product in the water supply industry. Since the use of the first electromagnetic flowmeter in 1989, Shanghai Waterworks has used more than 400 electromagnetic flowmeters from Kaifeng Open Flow Instrument Co., Ltd., ranging in diameter from DN15 to DN3000, mainly for water plants. Raw water trade measurement, twisting measurement, backwashing water metering, single-tube metering of pumping house, metering of plant water, and metering of factory water mains. There are also regional companies' pipe network connection boundaries for trade measurement of mutual water feeds. Due to the corrosive and abrasive nature of the water, in addition to the use of scraper electrodes for raw water and platinum electrodes for twisting, the rubber lining and stainless steel electrodes are generally used to meet the measurement requirements.

PREVIOUS：Application of plug-in electromagnetic flowmeNEXT：Electromagnetic flowmeters are described by c