Temperature and pressure compensation for flow rate

The orifice flow meter can be installed either before or after the control valve, but it is necessary to ensure there is enough straight pipe section; it is better to install it before the control valve, as this reduces the impact of the control valve’s opening and closing on flow measurement. The temperature and pressure sensors can be separated from the orifice plate, as long as they can reflect steam changes in real time......

A orifice plate is good in front of a control valve. The temperature and pressure measurement points for temperature and pressure compensation must follow the position of the orifice plate.

For steam flow regulation, devices such as pressure transmitters, thermometers, orifice plates, and control valves are commonly used. The installation positions should be as follows: 1. The orifice plate should be installed in front of the control valve, because if it is placed behind the control valve, the opening degree of the control valve will not remain constant; as a result, the inlet pressure to the orifice plate will be unstable, leading to inaccurate measurements by the orifice plate. 2. The pressure transmitter must be placed before the orifice plate, within a straight pipe section; only in this way can it ensure that the pressure measured is the actual inlet pressure at the orifice plate, thus guaranteeing accurate measurements. This pressure can then be used to perform accurate pressure compensation for the flow rate. 3. The thermometer should be installed after the orifice plate and before the control valve; more precisely, it should be placed after the straight section following the orifice plate. If it is installed in front of the orifice plate, it will inevitably affect the length of the straight section, and due to the presence of this thermometer, the required length of the straight section will not be sufficient. Therefore, the best installation order should be as follows: pressure transmitter, orifice plate, thermometer, control valve.

The flow meter is installed in front of the control valve, as the fluid passing through the control valve undergoes changes in state, which affects the flow meter’s measurement. Temperature and pressure sensors do not necessarily have to be installed together with the flow meter; they only need to be placed on pipes where the fluid conditions are the same. In other words, as long as the medium being measured by the flow meter, the temperature sensor, and the pressure sensor has similar properties, it’s not necessary for them to be installed together. It is common to use temperatures from a distant location for compensation, as long as the properties are similar enough. Hope it’s useful to you

What was said on the 5th floor is absolutely correct; what are you still hesitating about?

This post was last edited by HEJIYUER on 2016-2-23 00:42, version 1. Considering the requirements of the upstream resistance elements for the straight pipe section, the orifice plate is placed before the control valve, and the temperature sensor is located downstream of the orifice plate, which results in lower requirements. 2. The foundation of the orifice plate theory is \"conservation of mass\", whereas the density before and after a gas orifice plate changes. We measure the pressure upstream or downstream of the orifice plate (using a PT), and based on the differential pressure and the expansion coefficient ε, we can determine the other pressure, thereby \"balancing\" the mass equation; otherwise, it is not possible to calculate the orifice size. ISO specifies that P2/P1 should be greater than 0.75 in order to control the degree of gas expansion and prevent the density downstream from becoming too low, thus ensuring the \"accuracy\" of the backpressure density. The pressure should not be downstream of the valve; it can be on the orifice plate, outside the 2D area downstream thereof, which is permitted according to ISO standards. If the PT is located downstream of the control valve and pressure compensation is used based on the pressure behind the valve, the value entered for the orifice plate calculation is the pressure upstream of the orifice plate. Since the pressure drop across the valve can be significant, P2/P1 will be less than 0.75, resulting in poor accuracy. 3. Due to the throttling expansion through the orifice plate, the temperature does not drop much (as the pressure difference is small). When setting TE, the factors related to the straight pipe section are the main considerations. @jiaguoyun @Big Horse with Big Bow

I learned that initially, as long as the requirements for straight pipes were met, it didn’t matter where the pressure gauge and thermometer were placed – as long as they could reflect the actual conditions of the steam – before the control valve installed on the orifice plate. After reading the comments, I realized I had thought too superficially: lol. By the way: the original poster should set a best answer; the explanations on the fifth and ninth floors are both very professional.