Electromagnetic flowmeter use and maintenance troubleshooting

Case introduction

The electromagnetic flowmeter transmitter has a simple structure, no moving parts, and no resistance parts, throttling parts, etc. that hinder the flow of fluid. Therefore, it can be used to measure the flow of media such as mud, sewage, slurry, chemical fiber, etc., and when the fluid flows through the transmitter, there is almost no pressure loss, which can greatly reduce the consumption of motive power such as pumps. By selecting the appropriate lining material, the flow rate of corrosive media can also be measured.

The electromagnetic flowmeter can measure the flow rate of single-phase, liquid-solid two-phase conductive media, and the measurement is not affected by the temperature, viscosity, density, pressure, etc. of the measured medium. Therefore, after the electromagnetic flowmeter is calibrated with water, it can be used to measure the flow of other conductive media without correction.

The measuring range of the electromagnetic flowmeter is wide. The general range ratio is 10:1, and the highest range can be 100:1. As long as the medium flow rate is symmetrical to the axis of the pipeline, the volume flow rate measured by the electromagnetic flowmeter It is only proportional to the average flow rate of the medium and has nothing to do with the flow state of the medium. The electromagnetic flowmeter has fast dynamic response, can measure instantaneous pulsating flow, and has good linearity. The accuracy is generally 1.5 and 1.0. The above are the advantages of electromagnetic flowmeters, but there are also certain limitations and shortcomings: electromagnetic flowmeters cannot be used to measure gases, steam, and liquids containing a large number of bubbles. It cannot be used to measure liquids with low conductivity, such as petroleum products, organic solvents, etc. Due to the temperature limitations of the lining material and insulating material of the transmitter measuring tube, general electromagnetic flowmeters cannot be used to measure the flow of high-temperature media.

1. Principles for selecting electromagnetic flowmeters:

Electromagnetic flowmeters include two parts: a transmitter and a converter. The main problem in its selection is how to correctly select the transmitter and convert Just use it with the device. The selection of transmitter should be considered from the following aspects.

1.1 Selection of caliber and range:

When selecting a transmitter, you should first determine its caliber and flow measurement range, or determine the flow rate range of the fluid in the transmitter measurement tube. . Select the full-scale scale of the transmitter based on the maximum flow value expected in the production process, and the common flow rate of the transmitter in use can exceed 50% of the full-scale range to obtain higher measurement accuracy, and the transmitter range is determined Finally, the diameter is determined based on the relationship between the fluid flow rate and the head loss in the measuring tube. The flow rate is 2-4m/s as the most suitable. Usually the diameter of the transmitter is the same as or slightly smaller than the diameter of the pipe.

1.2 Selection of working pressure:

The pressure when the transmitter is used must be lower than the specified working pressure.

1.3 Temperature selection: The temperature of the measured medium cannot exceed the allowable temperature of the transmitter lining material. The medium temperature is also limited by the temperature resistance of electrical insulation materials, enameled wires, etc.

1.4 Selection of lining materials and electrode materials: The lining materials and electrode materials of the transmitter must be selected correctly according to the physical and chemical properties of the measured medium, otherwise the transmitter will be seriously damaged due to corrosion of the lining and electrodes. Soon to be damaged. Therefore, it must be based onThe anti-corrosion experience of the specific measurement medium during the production process, and the correct selection of the electrode and lining materials of the transmitter.

2. Use and maintenance of electromagnetic flowmeter

2.1 During the use of the electromagnetic flowmeter, when the power equipment near the transmitter has a strong ground leakage current, or There is a large stray current on the pipeline where the transmitter is installed, or electric welding is performed, which will cause an increase in interference potential, which will affect the normal operation of the flow meter. This should be paid special attention to during use.

2.2 When using, be careful not to allow the measured medium to contain a large amount of magnetic substances. After the instrument is put into normal operation, the potentiometers must not be adjusted at will, and the pipelines should be leak-free. These are all things that need to be paid attention to during use.

2.3 During the use of the electromagnetic flowmeter, scale may accumulate on the inner wall of the measurement conduit. The resistance of the scale layer is low. In severe cases, the electrode may be short-circuited, which may cause the flow signal to become smaller and smaller or suddenly drop. In addition, the lining of the measuring tube may also be corroded or worn, causing an electrode short circuit, causing serious measurement errors, and even the instrument cannot continue to work. Therefore, the transmitter must be regularly maintained and cleaned to keep the inside of the measuring tube clean and the electrode plate bright.