Electromagnetic flow meter is an instrument widely used in industrial flow measurement. Its measurement principle is based on Faraday's law of electromagnetic induction. In practical applications, the accuracy and stability of electromagnetic flow meter are affected by many factors, one of which is the requirement to install straight pipe sections. This article will elaborate on the requirements for the installation of straight pipe sections for electromagnetic flow meter from many aspects, with a view to providing help for the use and maintenance of electromagnetic flow meter.

1. Concept and function of straight pipe section

The straight pipe section refers to a straight section required before and after the fluid passes through the pipeline. Its length is generally more than 5 times the inner diameter of the pipeline. The main function of the straight pipe section is to gradually eliminate various disturbances caused by the fluid during the pipe flow process such as diffusion, expansion, contraction, etc., so as to stabilize the fluid flow and ensure measurement accuracy. The difference in the length of the straight pipe section will affect the measurement accuracy. If the length of the straight pipe section is insufficient, the measurement results may be biased. Therefore, the correct installation of the straight pipe section is an important guarantee for the measurement accuracy of the electromagnetic flow meter.

2. Requirements for straight pipe sections

(1) Length of straight pipe section

According to the requirements of the national standard JJG1033-2007 "Electromagnetic Flow meter", the electromagnetic flow meter should be installed in a straight pipe section, and the length of the straight pipe section should meet the following conditions:

A In any direction perpendicular to the measurement direction, when the inner diameter of the pipe is not less than 25mm, the length of the straight pipe section shall not be less than 10 times the inner diameter of the pipe, but shall not be less than 250mm;

B When the inner diameter of the pipe is greater than 25mm, the length of the straight pipe section shall not be less than 5 times the inner diameter of the pipe, but shall not be less than 250mm.

(2) Installation position of straight pipe section

The electrodes of the electromagnetic flow meter sensor should be installed in the vertical direction of the pipe to ensure measurement accuracy. At the same time, electromagnetic flow meter should avoid being installed in locations where pipes are bent or deformed, which will cause eddy currents in the fluid and thus affect measurement accuracy. If the electromagnetic flow meter must be installed in a curved or deformed position, the length of the straight pipe section needs to be increased to eliminate the influence of fluid eddy currents.

(3) Shape of straight pipe section

The shape of the straight pipe section should be kept as regular as possible, and sudden deformation, diffusion, shrinkage, etc. should not occur to reduce the disturbance of fluid flow. At the same time, fluid uniform distribution devices should be installed at the inlet and outlet of the straight pipe section to ensure

Uniform flow of fluid.

(4) Pipe material and inner surface finish of the straight pipe section The material of the straight pipe section of the electromagnetic flow meter should be non-magnetic to avoid interference from the magnetic field. Common non-magnetic materials include stainless steel, fiberglass, PVC, etc. At the same time, the inner surface of the straight pipe section should be kept smooth to avoid eddies, vortices and unstable flows caused by friction during fluid flow, which will affect the measurement accuracy. The inner surface roughness of the straight pipe section should generally be less than 0.01mm.

3. Installation method of straight pipe section

The straight pipe section should be installed in a manner that ensures a tight fit with the pipe without any gaps to avoid fluid leakage or other problems. At the same time, the installation of straight pipe sections should take into account the convenience of maintenance and replacement, so that they can be easily operated when maintenance or replacement is required.

The length of the straight pipe section is an important factor affecting the measurement accuracy of the electromagnetic flow meter. The longer the length of the straight pipe section, the better the stability of the fluid flow, the fewer eddies and eddies in the fluid, and the higher the measurement accuracy. Therefore, in practical applications, the appropriate straight pipe length should be selected according to specific conditions. At the same time, when installing an electromagnetic flow meter, you should follow the requirements of national standards and choose appropriate materials and installation methods to ensure the measurement accuracy and reliability of the electromagnetic flow meter.