Why does the electromagnetic flowmeter have errors? Why?


Release time:

2021-08-06

  Why does the electromagnetic flowmeter have errors? Why?

  Electromagnetic flowmeter is an instrument that uses the principle of electromagnetic induction to measure the flow of conductive fluid according to the electromotive force induced by conductive fluid passing through an external magnetic field. But when the electromagnetic flowmeter is used, there will be measurement error. What's going on? What caused it? Next, Kaifeng Kailiu Instrument Co., Ltd. will give you a specific explanation.

  1. The tube is not filled with liquid. The liquid in the test tube cannot be filled due to insufficient back pressure or poor installation position of the flow sensor. When there is a small amount of gas in the tube, the measurement result will deviate from the actual value, resulting in small error; When there are many gases, the measured value will be unstable and the output will shake. At this time, the measured value error is large and can not be used as the correct result.

  2. The measured liquid contains solid components. When this happens, the following problems usually occur in the instrument: slurry noise, dirt on the motor surface, lining worn or covered by sediment, reduction of flow cross-sectional area, conductive deposition layer or insulating deposition web rod electrode or lining. If there is conductive material in the deposition layer, the flow signal is likely to be short circuited, resulting in instrument failure.

  3. Improper selection of electrode and grounding ring materials. Due to the mismatch between the material and the measured medium, the parts of the electromagnetic flowmeter in contact with the medium include electrode and grounding ring. In addition to the corrosion resistance problem, the main reason is the electrode surface effect. Whether the electrode can reliably detect the flow signal is very important to the performance of the flowmeter. The grounding ring forms an electrical connection with the medium and is connected through the grounding wire and zero potential. When the process pipe connected to the sensor is plastic or pipe with insulating coating inside, the grounding ring must be installed, otherwise the instrument will not work normally.

  4. Uneven conductivity

  "Dosing" liquid is often injected into the liquid in the proportioning process, and the injected liquid is usually added by reciprocating pump. If the conductivity of the injected liquid is different from that of the main liquid, but the mixed liquid has not been mixed evenly, if the electromagnetic flowmeter sensor is installed downstream, the instrument output will shake due to the sharp change of conductivity. Although the liquid conductivity is greater than the threshold and changes slowly, it will not affect the normal measurement of the electromagnetic flowmeter. This phenomenon often occurs in the raw water adding coagulant process of water supply treatment engineering.

  The above points are the reasons for the errors of electromagnetic flowmeter. To sum up, we can see that they are mainly caused by improper selection, installation and use in the early stage. I hope you can avoid these problems in future operation.