丈量液体中含有气泡的现象 How to deal with the phenomenon of air bubbles in liquid measured by electromagnetic flowmeter
Causes: The composition of the bubble gas in the liquid has two ways: inhalation from the outside world and the dissolution of the gas (air) in the liquid into free bubbles. If the liquid contains large air bubbles, the entire electrode can be covered when the electrode is wiped, causing the flow signal input circuit to open instantly, causing the output signal to appear jerky. Judging method: The simplest judging method is to cut off the excitation circuit current of the magnetic field when encountering sloshing. If so, when the instrument still appears and is unstable, it is stated that most of them are formed due to the influence of bubbles. If this is the case, use a pointer multimeter to measure the electrode resistance. The loop resistance of the electrode can be measured higher than normal. However, the test needs the long-term accumulated test experience and data of professionals. 装在管系高点而潴留气体或外界吸入空气形成流量计晃动的话，改换装置位置是最彻底的处理办法，在管线最低点或采用U型管装置。 Solution: Regarding the condition that the measured medium contains air, if it is judged that it is caused by the position of the device, if the electromagnetic flowmeter is installed at the high point of the piping and the gas is trapped or the outside air is sucked into the flowmeter, the device position is changed. The most thorough treatment method is at the lowest point of the pipeline or adopt U-shaped pipe device. However, many applications are large calibers or the location of the device is not easy to change. It is recommended to install a gas collection bag and an exhaust valve upstream of the flow meter. A DN2200 caliber electromagnetic flowmeter, the fluctuation of the display due to air bubbles can reach 20-50%. After the exhaust device is installed, the measurement returns to normal.
--与流体接触零部件材料的选择 Electromagnetic flowmeter -selection of parts and materials in contact with fluid
Sensor parts that come in contact with the fluid include linings (or measuring tubes made of insulating materials), electrodes, grounding rings, and gaskets. The material's corrosion resistance, abrasion resistance, and upper temperature limit affect the instrument's resistance to fluids. Adaptability. Because there are few parts, simple shapes, flexible material selection, the electromagnetic flowmeter sensor has strong adaptability to fluids. (1) Lining material (or measuring tube in direct contact with the medium) Commonly used lining materials are fluoroplastics, polyurethane rubber, neoprene, and ceramics. In recent years, high-purity alumina 999.7% AI2O3) ceramics have been used for the lining, but only for small and medium-caliber sensors. Neoprene and FRP are used for non-corrosive or weakly corrosive liquids, such as industrial water, waste water, and weak acids and bases, and are the least expensive. Fluoroplastics have excellent chemical resistance, but poor abrasion resistance, and cannot be used for measuring slurry. The earliest application of fluoroplastics is polytetrafluoroethylene. Because it is only pressed against the measuring tube and has no adhesive force, it cannot be used in negative pressure pipes. Later, various modified varieties were developed to achieve injection molding and have Strong binding force can be used for negative pressure. Polyurethane rubber has excellent abrasion resistance, but poor acid and alkali corrosion resistance. Its abrasion resistance is equivalent to 10 times of natural rubber, suitable for coal slurry, ore slurry, etc .; the medium temperature should be lower than 40 ~ 60/70 ° C. Alumina ceramic has excellent abrasion resistance and abrasion and corrosion resistance to strong acids and bases. The abrasion resistance is about 10 times that of polyurethane rubber. It is suitable for corrosive mineral pulp; but it is brittle and negligent during installation and clamping It is fragile and can be used at higher temperature (120 ～ 140/180 ℃), but to prevent sudden temperature changes, such as steam sterilization, the general sudden change of temperature can not be greater than 100 ℃, and it takes 10min to raise 150 ℃.