Selection and working principle of thermal gas mass flow meter

Abstract: The selection and working principle information of thermal gas mass flow meters are provided by excellent flowmeter and flowmeter manufacturers and quotation manufacturers. Selection of thermal gas mass flowmeter 1. Range selection and diameter selection; 1. Look-up table method: Table 1: Selection table of air mass flow range. Table 2: Selection table of calibration flow range of four common gases. Table 3: Universal gas flow upper limit. for verification. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is the selection and working principle of thermal gas mass flowmeters. Selection of thermal gas mass flowmeter 1. Range selection and diameter selection; 1. Look-up table method: Table 1: Selection table of air mass flow range. Table 2: Selection table of calibration flow range of four common gases. Table 3: Universal gas flow upper limit. For the convenience of verification and use, the measuring range is standardized and checked when the instrument leaves the factory. The upper limit of the range will be reflected on the label and the verification certificate. 2. Determination of the upper and lower limits of the range: (1) Determination of the lower limit: Because the lower limit of the thermal gas mass flowmeter can measure extremely low flow rates, such as 0.05m/s, it is not necessary to consider the lower limit in the selection. (2) Determination of the upper limit: Generally, it is better to choose a higher one, and there should be a margin of more than 20%. Because the actual flow is easy to estimate the wrong u (3) Mixed gas range: For mixed gas, the user should give the molar ratio of the standard and the mixed gas, and then the manufacturer determines the range. Typically calibrated with air or nitrogen, then multiplied by a conversion factor. (4) Upper limit of explosion-proof products: the maximum flow rate should preferably be less than 34m/s. 2. Selection of installation methods: pipeline installation and plug-in installation; 1. In the gas industry, when the inner diameter of the pipeline <Φ250, generally use pipeline installation. 1. In diameter less thanΦIn the 250 pipeline, the cumulative flow calibration is generally used, and the pipeline type is commonly used in structure. 3. When the diameter is greater thanΦWhen the temperature is 250, the instantaneous flow calibration method is adopted, that is, the wind tunnel is used for calibration, so they are all plug-in structures. 4. If the on-site pipeline has been installed and no flange is installed, it can only be a plug-in structure. rightΦProducts with a diameter of less than 250 can still be calibrated by means of cumulative flow.ΦThe caliber above 250 is the instantaneous flow calibration method. 5. According to the operator's personal habits, the plug-in structure is adopted in the hope of convenient maintenance and installation. The range of plug-in structures can be extended toΦ15---Φ2000mm. 3. Selection of structure type: The first type is an integrated structure, that is, the sensor, the transmitter, and the display part are integrated, and the power supply is 220VAC or 24VDC. The display part is equivalent to a flow totalizer, displaying instantaneous flow and cumulative flow, setting alarm points and outputting linear 4--20mA signals. The second is a split structure, that is, the sensor, transmitter and display part are separated, and the display part is an independent intelligent flow totalizer, which displays instantaneous flow and cumulative flow, sets alarm points and outputs 4--20mA signal. The two parts are connected by three wires, and the transmitter is a three-wire system. The third type is the advanced armored type. That is, the sensor is armored, and the diameter is within 10. According to the pipe size, it can be selected due to different insertion depths.Φ10.Φ8,Φ6 The outer diameter of the sensor and the fixing method are with a 3/8 ball valve and a ferrule sealing structure. The transmitter and the sensor are separated and connected with a 1m cable, and the transmitter is independently installed beside the pipeline. The third structure is a special order, which is not listed in the selection table. 4. Selection of instrument output type: 1. Linear output; 2. Linear output in a certain range of the range; 3. Small signal removal; 4. Output filtering; 5. Communication interface. 5. Measurement unit and flow conversion table: generally choose the mass flow unit, namely kg/h. Select the standard unit that is Nm³/h. For comparison, it is necessary to convert the operating volume in m³/h converted to Nm³/h. When the flow is large, choose t/h or Nm³/h. When the flow rate is very small, choose the standard ml/min or ml/min. Symbol SCCM. Choose standard liter/min, L/min, symbol SLM. Standard cubic meter symbol SM³/min. 6. Selection of sensor materials: 1Cr18Ni9Ti is used for most of the supply, if there are special requirements, please negotiate with the manufacturer when ordering. 7. Scope of supply of special thermal gas mass flow meters (military, scientific research, supporting): (1) high frequency (quick response) sensor; (2) dust-proof sensor; (3) probe for flow field measurement; (4) ) Equipment matching special model. Working principle of thermal gas mass flowmeter: It is an instrument that measures gas mass flow using the principle of heat conduction. The sensor of the thermal gas mass flow meter consists of two reference grade thermal resistances (platinum RTDs). One is the mass velocity sensor T1, and the other is the temperature sensor T2 that measures the temperature change of the gas. When the two RTDs are placed in the measured gas, the sensor T1 is heated to a constant temperature difference ΔT above the gas temperature, and the other sensor T2 is used to sense the measured gas temperature. As the gas flows through, the electronic unit senses the decrease in ΔT and increases the energy to maintain the constant temperature difference ΔT. When the gas flow decreases, the electronic unit reduces the energy supply to the heating probe. The total energy supply to the heating probe is proportional to the gas mass flow rate. The microprocessor outputs a linear signal as the gas mass flow rate increases, and the gas flow takes away more heat. The temperature of the sensor T1 decreases. To maintain a constant temperature difference between T1 and T2, The heating power of T1 will increase. This heat transfer is proportional to the gas mass flow rate (density * flow rate). According to Kin's law of thermal effect, heating power P, temperature difference ΔT (T1-T2) and mass flow Q have a definite mathematical relationship. P/△T=K1+K2f(Q) K3K1, K2, K3 are constants related to the physical properties of the gas The above is the whole content of this article. You are welcome to inquire about the flowmeter selection and quotation of our factory. 'Selection and working principle of thermal gas mass flow meter'

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