对表前直管段长度的要求比较低。 First, the length of the straight pipe section The electromagnetic flowmeter has lower requirements for the length of the straight pipe section before the meter . Generally, for 90 ° elbow, T-shaped tee, reducer, fully open valve and other flow resistance parts, it should have a straight pipe length of 3-5D from the center line of the sensor electrode axis (not the sensor inlet end face); for different openings 10-degree valve requires a straight pipe length of 10D; generally 2D straight pipe length behind the sensor. When the valve cannot be fully opened, if the valve's interception direction is installed at 45 ° with the sensor electrode axis, the additional error can be greatly reduced.
Second, the installation site of the ordinary electromagnetic flowmeter enclosure protection level is IP65 (GB4208 dust and splash-proof water level), the requirements for the installation site are:
1) When measuring mixed-phase fluid, choose a place that will not cause phase separation;
2) Select a place where no negative pressure will appear in the measuring tube;
3) Avoid installing near electric equipment such as electric motors and transformers to avoid electromagnetic field interference;
4) Avoid installing in places with strong corrosive gas;
5) The ambient temperature should generally be in the range of -25 ~ 60 ℃, and avoid direct sunlight as much as possible;
6) Install in a place without vibration or small vibration. If the vibration is too large, fixed support should be added to the pipe before and after the sensor.
7) The relative humidity of the environment should generally be in the range of 10% ~ 90%;
8) Avoid installation in a place where it can be directly exposed to rain or submerged by water.
可以水平、垂直或倾斜安装。 3. Installation position and flow direction The electromagnetic flowmeter can be installed horizontally, vertically or obliquely. For horizontal installation, the sensor electrode shaft must be placed horizontally.
This can prevent the electrodes from being insulated for a short time due to the air bubbles entrained in the fluid; it can also prevent the electrodes from being covered by the deposits in the fluid. The sensor should not be installed at the highest point to avoid accumulation of air. It is installed at the highest point of the piping system. It is a bad installation position and should be avoided. When installed vertically, the flow direction should be upward, so that no flow or very low flow, the heavy solid particles entrained in the fluid will sink, and the lighter fatty substances will rise away from the sensor electrode area. When measuring liquid-solid two-phase flows such as mud and ore slurry, vertical installation can avoid solid phase sensation precipitation and uneven wear of the sensor lining. At the exit of a downward pipe, a bad installation position should be avoided.
There should be a certain back pressure at the installation place of the sensor. The direct exhaustion of the sensor outlet may easily cause the liquid in the measuring tube to be not full. This is a bad installation position 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 the inspection and adjustment of zero point when the liquid flow is stationary, small and medium pipe diameter should be installed as much as possible. When measuring fluids containing deposits, consider mounting methods that facilitate cleaning of the sensor.
V. Grounding In order to make the measurement accurate and the electrode will not be corroded by current, the electromagnetic flowmeter must be grounded separately, and the sensor and the fluid should be at about the same potential. In principle, the separation type electromagnetic flowmeter should be grounded on the sensor side, and the converter should be grounded on the same ground point. In most cases, the built-in reference electrode or metal tube of the sensor can ensure the potential balance. Therefore, the fluid in the tube can be grounded through the built-in reference electrode and metal tube, and the ground piece of the sensor can be connected to the ground.
If the sensor is installed on a pipeline with cathodic corrosion protection, in addition to grounding the sensor and the grounding ring together, a thick copper wire should also be used to bypass the sensor across the two flanges of the pipeline to make the cathodic protection current between the sensor and the sensor.
的主要优点如下： The main advantages of electromagnetic flowmeters are as follows:
1) The structure of the sensor of the electromagnetic flowmeter is simple, there are no moving parts in the measuring tube, and there are no throttling parts that hinder fluid flow. Therefore, it will not cause any additional pressure loss when the fluid passes through the flow meter, and it is one of the flow meters with the lowest energy consumption in the flow meter.
2) It can measure the flow rate of dirty media, corrosive media and suspended liquid-solid two-phase flow. This is because there are no obstructing flow parts inside the measuring tube of the instrument, and only the lining and electrodes of the measuring tube are in contact with the measured fluid, and the material can be selected according to the properties of the measured fluid. For example, using polytrifluoroethylene or polytetrafluoroethylene as the inner lining can measure various corrosive media such as acids, alkalis, and salts; the use of wear-resistant rubber as the inner lining is particularly suitable for measuring the wear of solid particles. Large liquid-solid two-phase flows such as mineral slurry and cement slurry, and various suspended liquids such as fiber-containing liquids and pulp.
3) The electromagnetic flow meter is a volume flow measuring instrument. During the measurement process, it is not affected by the temperature, viscosity, and density of the measured medium and its conductivity (within a certain range). Therefore, the electromagnetic flowmeter can be used to measure the flow of other conductive liquids only after it has been calibrated with water.
4) The output of the electromagnetic flowmeter is only proportional to the average flow velocity of the measured medium, and has nothing to do with the flow state (laminar or turbulent) in a symmetrical distribution. Therefore, the range of the electromagnetic flowmeter is extremely wide, and its measurement range can reach 100: 1, and some even reach the operational flow range of 1000: 1.
5) The electromagnetic flowmeter has no mechanical inertia and is sensitive in response. It can measure the instantaneous pulsating flow, and it can also measure the flow in both directions.
6) The caliber range of industrial electromagnetic flowmeters is extremely wide, from a few millimeters to several meters, and there are already real-flow calibration equipment with a caliber of 3m in China, which has laid the foundation for the application and development of electromagnetic flowmeters.