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The electromagnetic flowmeter must ensure that the measuring tube is always filled with the measured medium in the installation position
2012-3-6 9:08:25

的安装电磁流量度的正确安装对电磁流量计的正常运行极为重要,这里主要介绍电磁流量传感器和转换器的安装。 Installation of electromagnetic flowmeter The correct installation of the electromagnetic flow rate is extremely important for the normal operation of the electromagnetic flowmeter. Here we mainly introduce the installation of the electromagnetic flow sensor and converter.
The installation of electromagnetic flowmeter sensors should pay attention to the following issues:
First, the installation site of the ordinary electromagnetic flow sensor 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. If the sensor's enclosure protection level is IP67 (dust-proof and water-proof) or IP68 (dust-proof and diving-proof), the last two items may not be required.
Second, the length of the straight pipe section The electromagnetic flowmeter has a lower requirement 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. 3. Installation position and flow direction The electromagnetic flow sensor 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 flow sensor must be grounded separately, and the sensor and the fluid should be at about the same potential. ,原则上接地应在传感器侧,转换器接地应在同一接地点,在大多数情况下,传感器的内装参比电极或金属管能确保所许的电位平衡。 In principle, the separation type electromagnetic flowmeter should be grounded on the sensor side and the converter grounding should be 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 wire. 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.

在安装过程中一定要注意以下事项: The electromagnetic flowmeter must pay attention to the following during the installation process:
Try to stay away from equipment with strong electromagnetic fields. Such as large motors, large transformers, etc. There should be no strong vibration in the installation place, and the ambient temperature does not change much. Easy to install and maintain. The selection direction of the installation position must be consistent with the direction of flow of the measured medium in the track. The installation position must ensure that the measuring tube is always filled with the measured medium. Choose a place where the fluid flow pulse is small, that is, away from the pump and local resistance parts (valves, elbows, etc.). When measuring two-phase fluids, choose a place where phase separation is unlikely to occur. As far as possible, avoid installing the ground force which shows negative pressure in the pipe. In order to clean the electrode and measuring tube without interrupting the flow of the process pipeline, the sensor can be installed in parallel with a cleaning port. Requirements for upstream straight pipe section The sensor requires 5 times the diameter of the upstream straight pipe section. The sensor has no straight pipe section requirements downstream. The downstream non-straight pipe section will not affect the measurement accuracy of the flow meter. When the diameter of the upstream and downstream straight pipe sections does not pass through the sensor, a gradually expanding pipe or a reducing pipe should be installed, and its cone angle should be less than 150 (preferably 7-80) and then connected to the pipe. The flow signal generated by a grounded sensor is very weak, usually microvolts and millivolts, so preventing the influence of external electrical interference is an important factor in using a good flowmeter. The grounding of the sensor requires the following two aspects: Measured medium: The ground terminal of the sensor and converter and the shielding layer of the flow signal line must be in communication with the measured medium. Grounding: A. Use earth as the zero potential to reduce external interference. Generally, the process pipes are metal pipes, which are all grounded. However, in the case of large external electromagnetic field interference, especially when the stray leakage current on the pipeline is large, a separate grounding device should be provided. The grounding wire can be a multi-strand copper wire with a total cross-section greater than 4mm2. Never connect it to the common ground of the motor or other electrical equipment to avoid the effect of leakage current. The ground resistance core is less than 10Ω. B. When the process pipe is a metal pipe, the contact resistance between the front and rear pipes and the sensor housing should be almost zero.