The reason why gas mass flow meters (MFM) do not require temperature and pressure compensation lies in their direct measurement principle based on the law of heat conduction, which accurately calculates mass flow by sensing the heat carried away by gas molecules, fundamentally avoiding the interference of temperature and pressure on measurement results.
Taking MFM based on thermal principle as an example, its core components are heating wire and temperature sensor. When gas flows through the heating wire, it will take away some heat, causing the temperature of the heating wire to decrease. According to the law of heat conduction, the heat carried away by a gas is proportional to its mass flow rate. The temperature sensor monitors the temperature changes of the heating wire in real time and transmits the signal to the built-in circuit. The circuit calculates the temperature change rate and combines it with the gas specific heat capacity (Cp value) at constant pressure to directly determine the mass flow rate of the gas, without the need for additional measurement of temperature or pressure parameters. For example, in semiconductor manufacturing, MFM can accurately control the flow rate of silane gas, and even if the ambient temperature fluctuates by ± 10 ℃, the measurement error is still controlled within ± 0.5%.
Some MFMs use constant temperature difference or constant power technology to further optimize performance. The constant temperature difference type maintains a fixed temperature difference between the heating wire and the gas, and adjusts the heating power in real time to compensate for changes in flow rate; The constant power type fixes the heating power and calculates the flow rate by measuring the temperature difference. Both of these technologies have built-in digital signal processing algorithms that can automatically correct differences in gas thermal conductivity, ensuring measurement accuracy for different gases such as nitrogen and argon.
The non temperature pressure compensation feature of MFM makes it significantly advantageous in industrial scenarios. For example, in vacuum coating equipment, gas pressure may fluctuate significantly from vacuum to 10MPa, and traditional volumetric flow meters require frequent calibration. MFM can directly output the mass flow rate under standard conditions (such as sccm/slm) without pressure conversion. In addition, its wide range ratio (50:1) and fast response (<100ms) characteristics make it an ideal choice for dynamic processes such as combustion control and gas mixing.