Working principle of thermal flowmeter | What is a thermal mass flowmeter? Pay attention to the principle and advantages and disadvantages of thermal mass flow meters

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1. Measurement principle of thermal gas mass flowmeter

Thermal gas mass flowmeter is an instrument that can directly measure gas mass flow rate. Its measurement principle is based on heat transfer and electrical compensation mechanism, as follows: the core principle is to achieve constant temperature difference control through two thermal resistance sensors (temperature sensor and speed sensor) and a bridge circuit. The temperature sensor measures the temperature of the gas inside the pipeline, while the speed sensor is electrically heated to a temperature higher than the gas temperature and maintains a constant temperature difference. When the gas flow carries away the heat from the speed sensor, the bridge circuit maintains the temperature difference by compensating for heating, and the compensation power is proportional to the gas mass flow rate. The specific steps for configuring the sensor probe include two sensors: temperature sensor: usually using Pt1000 or Pt300, measuring the temperature of the gas medium (t ℃). Speed sensor: Pt20 is generally used to maintain a temperature higher than the temperature sensor through electric heating. The constant temperature difference control bridge circuit ensures a constant temperature difference (Δ t) between the two sensors. When gas flows through the fiber hole, the heat of the velocity sensor is taken away, and the bridge maintains the temperature difference by increasing the compensation heating power (Δ P). The compensation power is directly related to the gas mass flow rate. When the resistance difference triggers compensation at a temperature of t ℃, the resistance changes of the temperature sensor (Pt1000/Pt300) and the speed sensor (Pt20) are different, r

esulting in an unbalanced bridge. After the comparator detects the voltage difference, it triggers a new heating action to restore the constant temperature difference. Instantaneous flow formula for flow calculation model: (q_m=K cdot frac {Delta P} {C_p cdot Delta t}), where: (q_m): Instantaneous mass flow rate (kg/s) (K): Factory calibration correction factor (Delta P): Bridge heating power (kJ/s) (C_p): Gas specific heat capacity at constant pressure (kJ/(kg ·℃)) (Delta t): Temperature difference between two sensors (℃) Standard condition volume flow conversion: (q_ {VN}=q_m cdot frac {3600} {rho-N}), where: Hall shirt: (q_ {VN}): Standard condition volume flow rate (Nm ³/h) (rho-N}) uN): Gas standard density (kg/m ³) calibration and verification correction factor calibration: For different pipe diameters and gas media, the correction factor K is calibrated through experiments to ensure measurement accuracy. Circuit simulation testing: Simulate the effect of gas flow rate on the temperature of the speed measuring probe under different operating conditions, and verify the feasibility of instrument calibration. Application advantages: high sensitivity and repeatability: suitable for use in large diameter and low flow rate scenarios (such as ventilation ducts and smoke emission monitoring). Low pressure loss and flexible installation: With diverse mechanical structures and easy installation, it has minimal impact on fluid resistance. Wide applicability: It can measure multiple gases and meets the requirements of the JJG1132-2017 calibration regulation. Summary: The thermal gas mass flowmeter achieves high-precision measurement of gas mass flow rate through heat transfer and electrical compensation mechanisms, combined wi

Working principle of thermal flowmeter | What is a thermal mass flowmeter? Pay attention to the principle and advantages and disadvantages of thermal mass flow meters

1. Measurement principle of thermal gas mass flowmeter

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