1. What is a gas mass flow meter?

Mass flow meter, also known as Mass Flow Meter (abbreviated as MFM), is an instrument that accurately measures gas flow. Its measurement value is not inaccurate due to fluctuations in temperature or pressure and does not require temperature and pressure compensation.

2. What is a gas mass flow controller?

Mass flow controller, namely Mass Flow Controller (abbreviated as MFC), not only has the function of a mass flow meter, but more importantly, it can automatically control the gas flow, that is, the user can set the flow rate as needed, and the MFC automatically keeps the flow rate constant at the set value. Even if the system pressure fluctuates or the ambient temperature changes, it will not deviate from the set value. Simply put, a mass flow controller is a gas flow stabilizing device that can be manually set or connected to a computer for automatic control.

3. What are the main advantages of gas mass flow meters/mass flow controllers?

(1) Flow measurement and control will not be inaccurate due to fluctuations in temperature or pressure. For most flow measurement and control systems, it is difficult to avoid pressure fluctuations in the system and temperature changes in the environment and medium. For ordinary flow meters, fluctuations in pressure and temperature will cause large errors; for mass flow meters/mass flow controllers, they can generally be ignored.

(2) Automation of measurement control

The mass flow meter/mass flow controller can output the flow measurement value as a standard electrical signal. In this way, it is easy to realize digital display of flow rate, automatic measurement of accumulated flow rate, automatic data recording, computer management, etc. For mass flow controllers, automatic control of flow can also be achieved. Usually, the input and output signals of analog MFC/MFM are 0~+5V or 4~20mA. Digital MFC/MFM is also equipped with RS232 or RS485 digital serial communication port, which can be easily connected to the computer for automatic control.

(3) Accurate quantitative control

Flow mass flow controller can accurately control the given amount of gas, which is particularly useful for flow control of many processes and proportion control of different gases.

(4)Wide scope of application

It has a wide working pressure range, and the product can range from vacuum to 10MPa; it can be applied to a variety of gas media (including some corrosive gases, such as HCL); it has a wide flow range, the minimum flow range of the product can reach 0~5 sccm, and the maximum flow range can reach 0~1500 slm. The resolution of the flow display can reach 0.1% of the full scale, and the flow control range is 2 to 100% of the full scale (range ratio - 50:1), so it is widely used in many fields.

4. What is the concept of the working pressure difference range of the mass flow controller? 

The mass flow controller (MFC) is equipped with a gas flow adjustment valve. The valve can adjust the flow rate through the controller from zero to the full scale of the measurement. During the working process, a pressure drop, that is, the pressure difference, will occur between the inlet and outlet of the controller. The working pressure difference range of MFC is usually 0.1~0.3MPa. If the pressure difference is lower than the minimum value (0.1 MPa), the control may not reach the full scale value; if it is higher than the maximum value (0.3MPa), the flow rate may not be less than 2% F.S when closed. When users use MFC, regardless of whether the reaction chamber they are working in is vacuum or high pressure, the pressure difference between the inlet and outlet ends of the MFC should be maintained within the required pressure difference range, and the air pressure should be relatively stable.

5. When volatile liquids are used to evaporate steam, the air pressure is very low. How to customize low pressure drop products of mass flow controllers?

Some users use volatile liquid evaporation vapor as the gas source (such as acetone, etc.), but the air pressure is very low, and ordinary MFC cannot work properly. At this time, the user needs to make a special statement to the supplier to customize a low pressure drop mass flow controller. Usually, an MFC with a working pressure difference lower than 0.01MPa can be customized. At this time, the working pressure difference range of the MFC will also become smaller. Note: When using volatile liquid vapor, do not allow the vapor to condense in the MFC. Condensation will affect the normal operation of the MFC. To prevent condensation, the pipeline and MFC can be appropriately heated, but the working environment temperature of the MFC should usually not exceed 50°C. If the user wants the working environment temperature of the MFC to exceed 65°C, special high-temperature products need to be purchased.

6. Can mass flow controllers be used to control corrosive gases and special gases? How to choose sealing materials?

Mass flow controllers can be used to control various gases, including corrosive gases and special gases. However, it should be noted that for the use of corrosive gases and special gases, appropriate selection of models and sealing materials is required. When ordering, users need to make a special statement to the supplier about the gas used to avoid serious losses due to incorrect selection of models or sealing materials. Usually the wet materials in contact with the working gas of the gas mass flow controller are 316L stainless steel, polytetrafluoroethylene and sealing materials. The sealing materials are divided into two categories: metal seals and rubber seals. The material of metal seal is generally corrosion-resistant materials such as stainless steel, gold or nickel.

In principle, MFC with metal seal can be used for any gas, including various corrosive gases and special gases. For highly corrosive gases such as boron tribromide, boron trichloride, and hydrogen fluoride and metal oxide gases used in MOCVD, it is recommended to use metal-sealed MFCs. Since metal-sealed MFCs are more expensive, rubber-sealed MFCs are usually used in situations with low requirements. Unless otherwise stated, MFCs are sealed with fluorine rubber and can be used for most acidic and alkaline corrosive gases, such as halogen dry gases such as hydrogen chloride. Some other special corrosive gases require the use of special rubber. Ammonia gas-needs to use ammonia-resistant rubber, such as ethylene propylene rubber, neoprene rubber or nitrile rubber; organic solvent atmosphere (acetone, toluene, etc.)-needs to use silicone rubber; boron tribromide, boron trichloride, hydrogen fluoride, etc.-needs to use perfluorinated rubber.