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In the automatic detection and control of petrochemical production processes, it is necessary to measure the flow rate of various fluids in order to operate, control, and monitor them effectively. The calculation of the total amount of materials remains an important basis for energy management and economic accounting. It is evident that in production and scientific research experiments, flow rate is a very important parameter. Flow rate monitors serve as important tools for developing production, saving energy, improving economic efficiency, and enhancing management standards. Next, the editor from Gongcaiwang will introduce the application of flow sensors in the monitoring of ammonia gas flow rates. Ammonia, NH3, is a colorless gas. It has a strong pungent smell. Density 0.7710. Relative density 0.5971 (air = 1.00). It can be easily liquefied into a colorless liquid. It can be liquefied by applying pressure at room temperature (critical temperature: 132.4°C, critical pressure: 11.2 MPa, or 112.2 atmospheres). Boiling point -33.5°C. It can also easily solidify into a snow-like solid. Melting point -77.75°C. Soluble in water, ethanol, and ether. It decomposes into nitrogen and hydrogen at high temperatures, and has a reducing effect. As an important component of chemical products, ammonia is also one of the main raw materials for fertilizers, and its consumption in China is very high. Ammonia is also a commonly used gas in laboratories and production. The main method for producing ammonia involves heating a mixture of solid ammonium chloride and slaked lime, and then collecting the gas. Ammonia flow measurement: The flow box method calculates the net ammonia emission by comparing the differences in the measurement values obtained from two sampling disks placed vertically in the windward and leeward directions. Therefore, the ammonia concentration in both the windward and leeward directions needs to be measured simultaneously, and the measurement method must be accurate enough to reflect the concentration difference between these two directions. The total ammonia flow rate is estimated using the following formula based on the source strength value in the flow rate box: Where: Q represents the source strength, in units of ug/s; U is the average wind speed in the horizontal direction, in units of m/s; Cup is the average concentration in the upwind direction, in units of ug/m3; Cdown is the average concentration in the downwind direction, in units of ug/m3; Z is the height at which the sampling disk is placed, in units of m; D is the distance between two adjacent deoxygenation rods, in units of m. The working principle of the ammonia flow meter: It consists of vortex generators designed within the flow field, detection probes, and corresponding electronic circuits. When a fluid flows past a vortex generator, two alternating rows of vortices are formed on either side of it; these vortices are known as Karman vortex streets. Based on the theory of Karman vortex streets, it was proposed that the frequency of these vortex streets is proportional to the flow velocity of the fluid, and an equation relating frequency to flow velocity was given: f = St × V/d. Here, f represents the frequency at which the vortex streets occur (in Hz); V is the average flow velocity on either side of the vortex-generating body (in m/s); and St is the Strouhal number (a constant). These alternately appearing vortexes create a series of alternating negative pressures. When these pressures act on the sensing probe, they generate a series of alternating electrical signals. After being processed by a pre-amplifier through operations such as conversion, shaping, and amplification, a pulse frequency signal (or standard signal) that is proportional to the vortex activity is output. Regarding the use of ammonia flow meters, Gongcai.com recommends the American Siargo gas mass flow sensor – FS4001. This mass flow sensor utilizes Siargo’s proprietary MEMS flow sensor and packaging technology. The packaging box is made of chemically inert and heat-stable polycarbonate material. The high pressure rating is 5BAR (73 PSI), thanks to Siargo’s unique MEMS chip design, specialized packaging technology, and durable sensor housing. The measurement range of the sensor is from 0~30 sccm to 0~1000 sccm. The flow rate of each model is achieved through specially designed enclosures and smart electronic products, in order to attain the appropriate sensitivity. Key features of the gas mass flow sensor-FS4001: 1) The sensor has high sensitivity and a very low starting flow rate. 2) It uses thermal mass flow measurement technology, eliminating the need for temperature and pressure compensation and thus ensuring high measurement accuracy. 3) Multiple sensors are integrated on a single chip, which increases the sensor’s range ratio. 4) The sensor maintains high stability at zero point. 5) High stability across the entire range. 6) High accuracy and excellent repeatability throughout the range. 7) Low power consumption. 8) Low pressure loss. 9) Fast response time. Block diagram of the gas mass flow sensor-FS4001: The functional block diagram is shown below. A voltage converter related to power supply and signal transmission for the sensor drive circuit of MEMS sensor chips. The microcontroller processes the 19th letter of the English alphabet ； (Zooming, filtering, etc.) converts voltage into flow rate. The flow signal is sent in analog or analog and digital formats (RS232).