Who here knows about mass flow meters?

The \"SH.T 3104-2000 Code for Design of Installation of Petrochemical Instruments\" stipulates that: 5.0.9 The installation requirements for mass flow meters are as follows: 1. Mass flow meters should be installed in pipes that are completely filled with the medium to be measured. 2. Mass flow meters should be installed in horizontal pipes; when installed in vertical pipes, the fluid should flow from bottom to top, with an appropriate length of straight pipe at the outlet. 3. When used to measure volatile liquids (such as light hydrocarbons, liquefied gas, etc.), the pressure at the outlet of the flow meter should be higher than the saturated vapor pressure of the liquid. The flow meter should not be installed on the inlet pipe of the pump; when installed in a vertical pipe, it should be placed at the lowest point of the pipe. 4. The installation of Ω-tube mass flow meters in horizontal pipelines shall comply with the following requirements: a. When measuring gases, the Ω-tube should be placed above the pipeline; b. When measuring liquids, the Ω-tube should be placed below the pipeline. 5. When installing a straight-tube mass flow meter in a horizontal pipeline, due consideration must be given to the effect of the medium temperature on the transmitter; the ambient temperature at the transmitter should not exceed 60°C. 6. Mass flow meters with a diameter of 80 mm or more should be provided with supports. 7. When the liquid being measured may contain gases, a degasser should be installed. 8. It is advisable to install inlet and outlet isolation valves as well as bypass valves on the mass flow meter.

Due to the requirements of material balance, heat balance, storage, and economic calculations, it is mass or weight that is needed, not volume. Therefore, in measurement tasks, it is often necessary to multiply the measured volumetric flow rate by the density in order to convert it into a mass flow rate. Since density changes with the temperature of the fluid, in most cases, if the pipeline remains in a fixed operating condition, then the temperature and pressure of the fluid change little, and thus the variation in the fluid’s density is also small, allowing its effect to be ignored. In such cases, a volume flow rate measurement method is generally sufficient to achieve the measurement goal. However, when temperature and pressure change significantly, the density of the fluid changes greatly, making it meaningless to measure the volume flow rate and rendering accuracy impossible; in such situations, precise measurement is required, and a mass measurement method should be used.

When a fluid flows inside a rotating tube, it exerts a force on the tube walls; this force was discovered by Coriolis in 1832 while studying water wheels, and is commonly referred to as the Coriolis force. Mass flow meters operate on the principle of the Coriolis force. Inside the sensor, there are two parallel T-shaped vibrating tubes; a driving coil is located in the middle of these tubes, while sensing coils are placed at each end. When an excitation voltage supplied by the transmitter is applied to the driving coil, the vibrating tubes begin to oscillate back and forth periodically. As the fluid flowing through the sensor passes by these vibrating tubes, the Coriolis force comes into play, causing the tubes to vibrate torsionally. The sensing coils at the ends of the tubes generate two sets of signals with different phases, and the difference between these two signals is proportional to the mass flow rate of the fluid passing through the sensor. The computer calculates the mass flow rate passing through the oscillating tube. When different media flow through the sensor, the fundamental vibration frequency of the oscillating tube varies, and the density of the medium is determined based on this. The platinum resistor mounted on the sensor’s vibrating tube can indirectly measure the temperature of the medium. 　　A mass flow meter directly measures the mass flow rate of the medium passing through it; it can also measure the density of the medium and indirectly determine its temperature. Since the transmitter is an intelligent instrument based on a microcontroller, more than a dozen parameters can be derived from these three basic quantities for use by users. The mass flow meter features flexible configuration, powerful functions, and a high performance-to-price ratio, making it a next-generation flow meter. 　　A flow measurement instrument for measuring the mass flow rate in a pipeline. When the fluid under test experiences significant changes in parameters such as pressure and temperature, measuring only the volumetric flow rate can result in large measurement errors due to changes in the fluid density. In positive-displacement and differential-pressure flowmeters, the density of the fluid being measured can vary by 30%, which can result in a flow measurement error of 30–40%. With the increase in automation levels, many production processes have put forward new requirements for flow measurement. The chemical reaction process is controlled by the quality of the reactants (rather than their volume). The heating and cooling effects of steam and air streams are also proportional to the mass flow rate. Strict control of product quality, accurate cost accounting, and fuel quantity control for aircraft and missiles all require precise mass flow measurement. Therefore, a mass flow meter is an important flow measurement instrument. 　　Mass flow meters can be divided into two categories: one is the direct type, which directly outputs the mass flow rate ； Another category is the indirect or derived method, such as using a combination of ultrasonic flowmeters and density meters, with their outputs being multiplied together to obtain the mass flow rate. 　　Direct mass flow meters There are various types of direct mass flow meters, such as calorimetric, momentum, gyroscopic, and twin-impeller types.