Measurement accuracy analysis of flowmeter

In order to improve the measurement accuracy at the low end of the flow range, it is necessary to greatly improve the differential pressure measurement accuracy in the low differential pressure section. The most labor-saving and effective way is to add a low-range differential pressure transmitter to form a dual-range differential pressure transmitter. Pressure flow meter (2). (Engineering) Add a low-range differential pressure transmitter and a differential pressure transmitter. The reason why the indication error at the low end of the differential pressure cannot be further reduced is that its accuracy cannot be determined arbitrarily, and is affected by the area of ​​the bellows, etc. Restricted by factors, in fact, the area of ​​the bellows not only restricts the differential pressure value corresponding to the accuracy level, but also the differential pressure value corresponding to the influence of ambient temperature and long-term drift. In order to improve the differential pressure measurement accuracy when the relative flow rate is small, it is also an effective method to add a low-range differential pressure transmitter. For example, there is a steam flow measurement target, the maximum flow is 100^^, the minimum flow is 31/1^, the common pressure is 1.1^1^, the common temperature is 250 匸, the nominal diameter is 0^500, and the high-range differential pressure transmitter is 0, 075 Intermediate differential pressure transmitter, measurement range: 0〜1001^&, the low-range differential pressure transmitter is a 0.075-level low-differential pressure transmitter, and the measurement scale is set to 0〜3.751^3. In this way, under the command of the intelligent secondary meter, the two transmitters actively switch and cooperate with each other.〜On a scale of 100^, ^ is 1.25^. ① Countermeasures for other elements [3]〜5]. The measurement uncertainty of the economical differential pressure flowmeter is not only related to the uncertainty of the differential pressure measurement 4, but also related to the uncertainty of the flow density '1, the non-linearity of the outflow coefficient 0 and the expansion coefficient', for To eliminate or fundamentally eliminate the influence of these elements on the uncertainty of flow measurement, density compensation, outflow coefficient compensation, and expansion coefficient calibration can be performed in the secondary table according to the regular mathematical model [3]. The specific methods will be reviewed in Chapter 8 of this book. ② Avoid transmission distortion of differential pressure signal. In style. ^) In the relationship between the uncertainty of differential pressure measurement and the uncertainty of flow measurement shown, it is assumed that the differential pressure value input by the differential pressure transmitter is the same as the differential pressure value generated by the saving device. However, the pressure guiding tube is in the In the process of leading the differential pressure generated by the saving equipment to the transmitter, due to various reasons, it is easy to cause distortion of the differential pressure signal transmission. Among these reasons, there are unreasonable root valve selection devices, the slope of the pressure guiding pipe does not meet the requirements, the height of the condenser installation is different, the pressure guiding pipe is too long and the temperature of the transmission medium (liquid) in the pipe is not equal']. When the measured medium is dry gas, this kind of transmission distortion is usually negligible. When the measured medium is wet gas and steam, it will lead to transmission distortion if carelessness is taken.

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