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Mass flow controller
From GAWDAwiki
Mass flow controllers (MFCs) are closed-loop systems that measure and control the flow of liquid or gas. Both analog and digital MFCs are available. MFCs are commonly used as components of gas mixers, ambient air analyzers and gas dilution systems. A flow controller's accuracy is typically expressed as a percent of Full-Scale flow (% FS) and is dependent on the type of MFC as well as how it is calibrated [1].
Components
- The base houses the channels that make up the gas’ main flow path. All other parts of the mass flow controller are mounted on the base.
- The thermal sensor is made up of a small-bore tube with two resistance-thermometer elements wound around it. When an electric current is applied to the resistors, the tube is heated and then a temperature differential is created between the two resistors when gas passes through the tube. This is measured as an electrical signal.
- The bypass, also known as the flow splitter, ensures equitable flow rates between the sensor and the main flow path. This makes it possible to measure total flow rate by measuring only the gas that flows through the sensor.
- The control valve establishes the gas flow in response to a signal comparing the actual flow to the set point.
- Printed circuit board
Measurements
The temperature differential between the resistance elements in the thermal sensor depends on mass gas flow and is a function of its density, specific heat and flow rate. Mass flow is typically measured in standard cubic centimeters per minute (sccm) or standard liters per minute (slm).[2]
