What is a Mass Flow Controller?
A mass flow controller is a flow control device that measures mass flow and automatically controls it to a set flow rate. Fluids can be measured in two ways: mass flow (weight) and volume flow (volume). Mass flow controllers can accurately measure and control mass flow regardless of temperature and pressure variations. For this reason, mass flow controllers are widely used in semiconductor manufacturing processes, analytical equipment, and other situations where high repeatability and accuracy are required.
Mass flow is generally measured using thermal and Coriolis sensors. Thermal sensors measure mass flow based on the principle that temperature changes occur in response to fluid flow. Coriolis sensors, on the other hand, detect the Coriolis force generated by fluid vibration and measure mass flow based on this. The method should be selected according to the fluid (gas or liquid) and the conditions of use.
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Mass Flow Controller Structure and Operation
The main components of a typical thermal mass flow controller are a flow sensor, control valve, and bypass. Operation is automatic with the following steps.
- Mass sensor is heated to measure fluid movement (mass flow rate)
- A bridge circuit converts the mass flow rate into an electrical signal
- Amplifies the mass flow signal converted to an electrical signal with an operational amplifier
- Converts to a digital signal with an AD/DA converter
- Compares the set flow rate with the current flow rate in an arithmetic circuit
- PID control is used to drive the valve actuator
- Repeat steps 1 to 6 (feedback control)
Principle of Mass Flow Controller Measurement
The flow sensor principle of the thermal mass flow controller is as follows
- Two electric heating wires are wound around a stainless steel capillary tube, which is heated to the same temperature. These electric heating wires are placed on the path through which the fluid flows.
- When the gas is shut off, the upstream and downstream electric heating wires maintain the same temperature and are not out of balance.
- However, as the gas flows, the upstream electric heating wire loses heat from the gas and flows downstream, changing the balance.
- To detect this change, a bridge circuit installed in the capillary tube is used. The bridge circuit is used to measure electrical signals and compares the signals from the upstream and downstream electric heating wires.
- The change in balance due to gas flow is converted into an electrical signal by a bridge circuit. This signal is measured as a mass flow rate.
Thermal mass flow controllers use this heat-based measurement principle to measure flow rates. This measured flow rate information is then fed back to the subsequent control circuitry, which performs control actions to bring the valve closer to the set flow rate by controlling the valve. Mass flow controllers from different companies may have different features depending on the flow sensor design and patented technology.
Lintec Mass Flow Controller Features
Lintec’s mass flow is based on a unique low-temperature sensing structure, and we were the first in the world to develop a liquid mass flow controller, as well as gas flow control.
Lintec’s mass flow controllers employ a low-temperature sensing structure (ambient temperature compensated sensor) to enable high-precision, high-speed measurement. The principle of this sensor is a unique structure that feeds back ambient temperature to the flow sensor so that the temperature of the flow sensor does not rise beyond what is necessary.
- Less thermal damage to the sensor (longer life): The low-temperature sensing structure keeps the temperature of the flow sensor low. This results in less thermal damage to the sensor and longer physical life.
- Low risk of thermal decomposition of fluids (e.g. ozone can be controlled): Since the measurement is taken at lower temperatures than typical mass flow controllers, it is ideal for flow control of gases with a high risk of thermal decomposition, such as ozone. Minimizes thermal effects on the fluid.
- Capable of high-speed flow control: The low-temperature sensing structure enables a response time that is overwhelmingly faster than that of conventional thermal sensors. Excellent performance when high-speed flow control is required.
This low-temperature sensing structure enables highly accurate and fast flow measurement and control.
Gas and liquid gas mass flow controller
Gas mass flow controllers for gases are sometimes abbreviated as gas mass. It is a fluid control device developed for precise gas fluid control and predates liquid mass flow controllers. Gas changes its volume under the influence of temperature and pressure according to Boyle-Charles’ law, but gas mass flow controllers provide precise flow measurement unaffected by temperature and pressure, and can automatically control to a set flow rate by means of a built-in control valve. Thermal mass flow controllers, which utilize constant pressure specific heat, are the main type of mass flow controllers.
Liquid mass flow controllers, abbreviated as liquid mass, were developed for precise liquid flow control. LINTEC was the first in the world to develop a thermal type liquid mass flow controller, contributing to technological innovation in the semiconductor industry. In addition to the thermal type, the Coriolis type and differential pressure type also exist.
- Gas gas mass flow controllers are fluid control devices dedicated to gases, enabling precise flow control without being affected by temperature or pressure.
- Liquid mass flow controllers, abbreviated as liquid mass, enable precise liquid flow control. LINTEC was the first in the world to develop a thermal liquid mass flow controller.