How to install electromagnetic flowmeter sensor
(1) Installation location
Generally, the protection level of the electromagnetic flowmeter sensor shell is IP65 (dust and water spray level specified in GB 4208), which has the following requirements for the installation site.
1) When measuring mixed-phase fluids, choose a place that will not cause phase separation; when measuring two-component liquids, avoid installing downstream that has not been uniformly mixed; when measuring chemical reaction pipelines, install it downstream of the fully completed section;
2) Avoid the negative pressure in the measuring tube as much as possible;
3) Choose a place with little vibration, especially for integrated instruments;
4) Avoid large motors, large transformers, etc. nearby to avoid electromagnetic field interference;
5) It is easy to realize the place where the sensor is grounded separately;
6) Avoid high concentration corrosive gases in the surrounding environment as much as possible;
7) The ambient temperature is in the range of -25 / -10 ~ 50/60 ℃, the temperature of the integrated structure is also subject to electronic components, and the range should be narrower;
8) Environmental relative humidity is in the range of 10% to 90%;
9) Avoid direct sunlight as much as possible;
10) Avoid rainwater, not being submerged by water.
If the protection level is IP67 (dust-proof and immersion-proof) or IP68 (dust-proof and submersible), the above two requirements 8) and 10) are not required.
(2) Length requirement of straight pipe section
In order to obtain normal measurement accuracy, a certain length of straight pipe section should also be upstream of the electromagnetic flowmeter sensor, but its length is lower than most other flow meters. After 90 ° elbow, T-shaped tube, concentric reducer, and full-open gate valve, it is generally considered that as long as the straight pipe section is 5 times the diameter (5D) length from the center line of the electrode (not the connection surface of the sensor inlet end), the valve with different opening degrees Need 10D; the downstream straight pipe section is (2 ~ 3) D or no requirement; but to prevent the butterfly valve valve from reaching into the sensor measuring tube. The lengths of the upstream and downstream straight pipe sections proposed by various standards or verification regulations are also inconsistent. The requirements are higher than usual as shown in the following table. This is because in order to ensure that the requirements of the current 0.5-level precision instruments are met. ISO 6817 is a standard for using electromagnetic flowmeters. The standard believes that there should be at least 10D straight pipes for any type of flow disturbances, and performance changes can be guaranteed not to exceed 1%. ISO 9104 and JJG 198 are documents proposed to evaluate the performance of electromagnetic flowmeters; the straight pipe length of JJG 198 listed in the table is an instrument with an accuracy of 0.5 and above.
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