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How to choose the instrument for measuring the chilled water cooling quantity

1 electromagnetic flowmeter, electromagnetic flowmeter has obvious advantages in the flow measurement of chilled water. The advantages of the electromagnetic flowmeter described in Section 4.2.3 can be revealed in the measurement of chilled water flow, among which Corrosion problems are especially important for brine chilled water. In high-rise buildings, some air-conditioning water pressure is high. At this time, it can be negotiated with the instrument manufacturer to specially manufacture electromagnetic flowmeters that can withstand pressure requirements. In the specific design fashion, the following issues need to be considered.
a. The choice of measuring tube lining. If the chilled water is fresh water, the rubber lining is used and the price is lower. If the chilled water is brine, a PTFE liner must be selected. If both fresh water chilled water and brine are measured, a PTFE liner must be selected.
b. The electromagnetic flowmeter measures the moisture resistance of the excitation coil of the tube. There are two common methods for the excitation coil in the electromagnetic flow sensor to be sealed in the housing. One is to use the upper and lower halves of the outer casing, and the sealing strip is pressed by screws to achieve sealing; the other is to use the housing welding sealing method. , to isolate the coil from the outside world. The latter is more reliable, completely eliminating the breathing phenomenon of the coil cavity and preventing the intrusion of external moisture. However, in the production process, the cavity around the coil is always filled with air, and the water vapor content therein varies with the atmospheric temperature and relative humidity during assembly. If the water vapor content is high, condensation will likely occur after the flowmeter is put into use due to a decrease in temperature in the conduit and cavity.
Vent valve
The misoperation caused the negative pressure in the tube to cause the coil to get wet and the insulation to be destroyed. Thus, when the chilled water temperature is low (some manufacturers are bounded by 0 ° C), the air in the cavity is replaced with nitrogen, and at a lower temperature (such as -10 ° C or lower), Methyl silicone oil (some manufacturers monthly transformer oil) is filled. Different manufacturers have different practices, but the general one is that the enclosed drying medium does not escape, and the coil insulation does not decrease during long-term use.
c. The lining is subject to negative pressure problems. When the chilled water flow is measured normally, the measuring tube itself is not subjected to negative pressure. Only when the water in the pipeline is discharged, the venting valve at the highest point of the pipeline is forgotten to open, so that the negative pressure occurs in the upper part of the pipeline for the same reason. Negative pressure also occurs in the hot water pipe.
The negative pressure inside the pipe that KROHNE's several linings can withstand is listed in Table 4.3. Therefore, once the negative pressure inside the pipe exceeds the specified value, it is possible to cause the inner lining of the measuring tube to fall off instantaneously, and therefore, it should be avoided. Another way to solve this problem

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