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Description of electromagnetic flowmeter selection and installation precautions

Electromagnetic flowmeter is a new type of flow measuring instrument developed rapidly with the development of electronic technology in the 1950s and 1960s. An electromagnetic flowmeter is an instrument that applies the principle of electromagnetic induction to measure the flow of a conductive fluid based on the electromotive force induced by the conductive fluid through an applied magnetic field. The structure of the electromagnetic flowmeter is mainly composed of a magnetic circuit system, a measuring conduit, an electrode, a casing, a lining and a converter.

Selection:

1. Understand the process parameters

(1) Understand the name of the liquid to be tested (provided by the user)

(2) Understand the maximum flow rate, common flow rate, and minimum flow rate of the liquid to be tested (provided by the user)

(3) Understand the process diameter (provided by the user)

(4) Understand the medium temperature (provided by the user)

(5) Understand the medium pressure (provided by the user)

(6) Understand the conductivity of the fluid being tested (provided by the user)

(7) Understand whether there is a negative pressure condition (provided by the user)

2. Preliminary selection

(1) Determine whether to use an electromagnetic flowmeter (determined by the salesman) based on the name and nature of the measured medium

Note: Electromagnetic flowmeters can only measure the flow of conductive liquids, while gases, oils and most organic liquids are not in the case of general conductive liquids.

(2) Determine the electrode material based on the known properties of the medium

Note; the company generally provides four kinds of electrodes, such as stainless steel, Hastelloy, titanium and tantalum. Which electrode should be used according to the nature of the medium.

(2) Determine whether to use rubber or PTFE liner according to the temperature of the medium (determined by the salesperson)

Note: The temperature resistance of rubber should not exceed 80C;

PTFE with temperature resistance 150C, instant resistance to 180C;

Urban sewage can generally be rubber lining and stainless steel electrode

(3) According to the known medium pressure, select the body flange specification (determined by the salesperson)

Note: The electromagnetic flange specification is usually when the diameter is from DN10-250, the rated pressure of the flange is ≤1.6Mpa;

When the diameter is from DN250-1000, the rated pressure of the flange is ≤1.0Mpa;

When the actual pressure of the medium is higher than the above-mentioned pipe diameter-pressure corresponding range, it is a special order, but the maximum pressure shall not exceed 6.4Mpa.

(4) Determine the conductivity of the medium

Note: (1) The conductivity of the electromagnetic flowmeter must not be less than 5uS/cm.

(2) The conductivity of tap water is about tens to hundreds of uS/cm. Generally, boiler soft water (deionized water) conducts electricity, and pure water (highly distilled water) does not conduct electricity.

(3) The conductivity of gases, oils and most organic liquids is much lower than 5 uS/cm and is not conductive.

3. Understand user requirements

(1) Understand whether it is a combined local display or a split remote display (provided by the user)

Note: Please understand the maximum distance when displaying for remote remote transmission. The maximum separation distance is 100 meters.

(2) Know if additional features are required (provided by the user)

Note: 1. The electromagnetic flowmeter itself has upper and lower limit flow alarm, frequency and current output functions, no special order is required.

2. The electromagnetic flowmeter housing seal protection grade is IP65 and IP68. When selecting the submersible IP68, it is a special order.

3. When the electromagnetic flowmeter is to be connected to the computer, the RS-485 communication port needs to be added, which is a special order.

4. Selection: After the above steps, the model specifications of the electromagnetic flowmeter can be finalized.

Installation should pay attention to the problem:

Before installing the electromagnetic flowmeter, you must have a good understanding of its installation method. Generally, the flow rate of the medium used for industrial electromagnetic flowmeter is 2~4m/s. Under special circumstances, the minimum flow rate should be no less than 0.2m/s, and the highest should be no more than 8m/s. Therefore, you need to pay more attention during the installation process.

1. Non-full pipe flow can not use electromagnetic flowmeter. If it is not full, the outlet can be changed to a higher level as shown above. When it is still, the water is still full. If it does not flow, the flowmeter will display zero.

2. The flange of the electromagnetic flowmeter needs to be installed. It is enough to screw the flanges on both sides, so the installation is very simple.

3. Ensure that the pipe at the installation location is full.

4, to ensure that the installation position to the water direction 10 times the diameter of the straight pipe section, the rear 5 times the diameter of the straight pipe section (5D after the first 10D).

5. The reason for the requirement for full pipe is to ensure that all the pipes are water. If there is gas, it is not allowed. The flowmeter calculates the flow according to the full pipe.

When installing the electromagnetic flowmeter, it should also be noted that there should be no strong leakage current on the pipeline where the sensor is installed. It should be kept away from the equipment with electromagnetic flowmeter as much as possible to avoid electromagnetic field interference.

At the same time, after the installation work is completed, it is necessary to be able to carry out a detailed inspection, and the electromagnetic flowmeter can be used only after the inspection is confirmed.

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