Electromagnetic flowmeter performance and resolution

Case introduction

Electromagnetic flowmeters are currently used very widely. With the advancement of science and technology and the continuous improvement of processing levels, the functions of electromagnetic flowmeters have become more powerful and the accuracy has improved than before. How to judge whether an electromagnetic flowmeter is good or not? Bad or not. There are many methods, and the means are also different. In the testing stage of the production workshop, the resistance of the magnetic coil and the contact resistance between the electrode and the liquid are generally measured with a multimeter to comprehensively judge the performance of the instrument.

The uniqueness of the electromagnetic flowmeter is reflected in the following points, because the electromagnetic flowmeter is a volume flow measurement instrument. During the measurement process of the instrument, it is not affected by the measurement medium. temperature. The influence of physical properties (within a certain range) such as viscosity, density and conductivity. Therefore, after the instrument is calibrated with water, it can be used to measure the flow rate of other conductive liquids without the need for additional corrections. The transmitter of the electromagnetic flowmeter has a simple structure, no moving parts, and no throttling parts that hinder the flow of fluid, so it will not cause any additional pressure loss when the fluid passes through, and it will not cause wear, blockage, etc. It is especially suitable for measuring liquid-solid two-phase fluids such as slurry with solid particles, sewage, and various viscous slurries. Similarly, since there are no moving parts in its structure, the electrodes can be made by attaching a corrosion-resistant insulating lining and selecting corrosion-resistant materials to achieve good corrosion resistance, making it suitable for measurement of various corrosive media.

1. First select a flow meter with corrosion resistance

1) Instrument selection for general acidic media. Oval gear flowmeters made of acid-resistant steel, such as vortex flowmeter sensors and turbine flow sensors, have acid-resistant steel in contact with the fluid. They can be used for general acidic liquids and gases, and can also meet the needs of accurate measurement of acidic liquids.

2) Instrument selection for conductive liquids. First, choose an electromagnetic flowmeter with a corrosion-resistant lining material for the measuring tube. The one with good corrosion resistance is polytetrafluoroethylene. There are also many kinds of electrode materials, such as molybdenum-containing acid-resistant steel 0Cr18Ni12MoTi, 316L, Hastelloy B, Hastelloy C, titanium, platinum, platinum-iridium alloy, etc., which can meet the needs of most corrosive media.

3) Instrument selection for non-conductive liquids. Optional clamp-on ultrasonic flowmeter in which the fluid does not come into direct contact with the meter is suitable for measuring various corrosive media.

4) Instrument selection for corrosive gases. Generally, a throttling differential pressure flowmeter is used. On the basis of the pipeline being lined with rubber, glass, or polytetrafluoroethylene, the transmitter diaphragm is initially made of molybdenum-containing stainless steel, and later a layer of polytetrafluoroethylene is affixed to the diaphragm. Fluorine vinyl isolation diaphragm, but corrosion still exists. When the instrument manufacturer continued to improve the diaphragm material and still could not solve all the problems, a solution was proposed to use isolation fluid to isolate instruments with poor corrosion resistance from corrosive fluids. The commonly used isolation fluid for highly corrosive gases is fluorine oil, but fluorine oil is very expensive. In addition, the isolation container must be made of corrosion-resistant materials, which makes the instrument more expensive.'

2. Select a measurement plan suitable for special working conditions.

In special working conditions, sometimes choosing a flow meter with corrosion resistance still cannot solve the problem. This requires an in-depth understanding of the process flow and related medium characteristics to avoid the problem of corrosion resistance of flow measurement instruments. For example, the flow into a sewage treatment plant generally needs to be measured in order to control the total amount of pollutants discharged. Sewage is generally either acidic or alkaline, and accordingly an appropriate amount of alkali or acid must be added to neutralize it. Then, considering the corrosion of measuring instruments by sewage, it is of course better to choose the flow detection point after neutralization.