Question 1

What Is the Working Principle of Thermal Mass Flow Controller?

Accepted Answer

The principle of a thermal mass flow controller is based on the thermal diffusion effect and the principle of thermal equilibrium. It achieves high-precision control of mass flow rate by measuring the disturbance of the thermal field caused by gas flow.

Its core sensor typically consists of a heating element and symmetrically distributed temperature sensors. When the gas is stationary, the thermal field between the heating element and the temperature sensors is symmetrically distributed. When the gas flows, fluid molecules carry away heat, causing the temperature downstream of the heating element to drop, forming a temperature difference related to the flow rate.

According to King’s Law, the gas mass flow rate has a linear relationship with the temperature difference and the heating power. By measuring the temperature difference or adjusting the heating power, the gas mass flow rate can be calculated.

Question 2

Quantitative Control of Gas Flow

Accepted Answer

Gas flow controllers require accumulated gas volume values in some applications. How can the accumulated gas volume be precisely controlled?

Our MFC function includes a feature that automatically sets the instantaneous flow rate to 0 once the accumulated flow rate value is reached.

First, set the desired accumulated flow rate (accumulated gas volume) within the meter. Then, set the real-time intake flow rate (instantaneous flow rate). MFC will activate the accumulation function, and automatically stop gas supply once the accumulated flow rate reaches the set target value.

This control method can be operated on the meter’s screen or controlled via a host computer, and is equipped with 485 Modbus communication.

Guide to Connecting a Thermal Mass Flow Controller to a PLC

7 Critical Gas Detector Calibration Errors to Avoid: An Expert Guide

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