Jin He summarizes the points of attention in the installation process of the electromagnetic flowmeter

Abstract : Electromagnetic flowmeters are widely used in many fields such as sewage, fluorine chemicals, production water, tap water industry, medicine, steel, and so on. Because the principle determines it can only measure conductive liquid. Although it is much better than other types of flowmeters in terms of reliability and stability, customers will still have some problems during actual use. This paper will discuss in detail the selection and installation of electromagnetic flowmeters.

Install electromagnetic flowmeter sensor installation should pay attention to the following questions:

First, the installation place of the general electromagnetic flow of the shell protection class IP65 (GB4208 dust-proof splash-proof level), the installation site requirements are:

1) When measuring mixed phase fluids, select sites that will not cause phase separation;

2) Select the place where the negative pressure will not appear in the measuring tube;

3) Avoid installing near electric equipment such as motors and transformers to avoid electromagnetic interference;

4) Avoid installation in places with strong corrosive gas around;

5) The ambient temperature should generally be in the range of -25 ~ 60 °C, as far as possible to avoid direct sunlight;

6) Install in a location where there is no vibration or vibration. If the vibration is too great, the pipes in front of and behind the sensor should be fixedly supported.

7) The relative humidity of the environment should generally be in the range of 10% to 90%;

8) Avoid installing in a place where it can be directly rained or immersed in water. If the sensor enclosure rating is IP67 (dust-proof and anti-submerged) or IP68 (dust-proof submersible), the last two items may not be required.

Second, straight pipe length electromagnetic flowmeter on the table straight pipe length requirements are relatively low. Generally, for flow resistances such as 90° elbow, T-shaped tee, reducer, full-open valve, etc., the straight line length from the sensor electrode shaft center line (not the sensor inlet end face) should be 3-5D; for different open The degree of the valve, it requires a 10D straight pipe length; sensor should generally have 2D straight pipe length. When the valve cannot be fully opened, the additional error can be greatly reduced if the valve closing direction is set to 45° with the sensor electrode shaft.

Third, the installation position and flow direction The electromagnetic flow sensor can be installed horizontally, vertically or obliquely. When installing horizontally, the sensor electrode shaft must be placed horizontally.

This prevents short-term insulation of the electrodes due to air bubbles entrained in the fluid; it also prevents the electrodes from being covered by deposits in the fluid. The sensor should not be installed at the highest point to avoid gas accumulation and should be installed at the highest point of the piping system.

For vertical installation, the flow direction should be upward, so that with no flow or small flow, the heavier solid particles entrained in the fluid will sink, while the lighter fat species will rise off the sensor electrode area. When measuring liquid-solid two-phase flow such as mud and pulp, vertical installation can avoid solid phase sedimentation and uneven wear of the sensor lining. At a downpipe outlet, poor installation locations should be avoided.

The sensor installation site should have a certain back pressure. The sensor outlet directly draining can easily cause the liquid in the measurement tube to be less than full. It is a poor installation location and should be avoided.

To prevent negative pressure in the sensor, the sensor should be installed behind the pump and not in front of the pump.

Fourth, install the bypass pipe In order to facilitate checking and adjusting the zero point when the liquid flow is at rest, the bypass pipe should be installed as small as possible. When measuring fluids containing sediment, consideration should be given to the ease of installation of the sensor.

V. Grounding In order for the measurement to be accurate and the electrode not to be galvanic, the electromagnetic flow sensor must be grounded separately and the sensor and the fluid are at approximately the same potential. Separate electromagnetic flowmeters, in principle, should be grounded on the sensor side, the converter should be grounded at the same ground point, in most cases, the sensor's built-in reference electrode or metal tube can ensure that the potential balance. Therefore, the fluid in the tube can be grounded via the built-in reference electrode and the metal tube, and the grounding plate of the sensor can be connected to the grounding wire.

If the sensor is installed on a pipe with corrosion protection with a cathode, in addition to grounding the sensor together with the grounding ring, use a thick copper wire to bypass the sensor across the two flanges of the pipe so that the cathodic protection current is between the sensor and the sensor.

It is normal for the electromagnetic flowmeter to display a negative value during installation or operation. Reinstall it. The sensor is not installed according to the flow direction markings, resulting in the opposite direction of measurement. There is definitely a way to solve the problem of failure, so do not worry about this.

Measuring pipe empty pipe or not full of pipe, there is gas. At this time, the flow meter will show a negative number or a flow value that is suddenly large or small. The sensor signal line is reversed. Since the electromagnetic flowmeter has the forward and reverse flow measurement function, the reverse flow rate is displayed. Replace the signal line. Fill the pipeline with the measured medium and allow the flowmeter to have measurement conditions.

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