The working principle and structure of the heating element of thermal gas mass flow meter

Time: 2024-08-01
Equipment Configuration:Thermal gas mass flow meters

Thermal gas mass flow meter measures gas mass flow directly by double RTD structure, working based on thermal diffusion principle. Its structure includes sensor assembly, circuit system and case protection, and is widely used in petrochemical, pharmaceutical and other fields.

Project Overview

The heating element of a thermal gas mass flow meter (usually including two thermal resistors or RTDs, such as PT100) is its core component. They work based on the principle of thermal diffusion and are used to directly measure the mass flow of gases. The following is a detailed description of its working principle and structure:

Working principle:

1. Dual thermal resistor structure: Thermal gas mass flow meters usually contain two reference-level thermal resistors. (RTD), one of which is called the speed sensor (RH) or heating element and the other acts as a temperature sensor (RMG or R5[T]) to monitor the fluid temperature.

2. Heating and temperature difference maintenance: The speed sensor (RH) will be heated to a constant temperature higher than the fluid temperature. As the gas flows through the heating element, it removes heat, causing the temperature of the heating element to drop. In order to keep the temperature of the heating element constant, it is necessary to adjust the current applied to the heating element. The current increment of this adjustment is proportional to the gas mass flow rate flowing through the sensor.

3. Heat transfer and flow calculation: The faster the flow rate of the gas, the more heat is taken away, and the greater the current required for supplementary heating. By measuring the change in current required to maintain a constant temperature difference, the mass flow rate of the gas can be calculated. This process involves heat transfer phenomena such as heat conduction and convection heat transfer.

4. Thermal diffusion principle: Thermal flow meter can also be based on the thermal diffusion principle, that is, when the fluid flows through a heating object, the heat loss of the heating object is in a certain proportion to the flow rate of the fluid. By monitoring the heat loss rate Measure flow indirectly.

Structure:

  • Sensor component: consists of two thermal resistors (RTD), embedded inside the measuring pipe or installed in an intrusive manner. These sensors are constructed from high-quality materials such as platinum to ensure accurate and stable thermal performance.

  • Circuit system: including bridge circuit, operational amplifier, PID controller and drive circuit, used for temperature control and signal processing of heating elements. Changes in the unbalanced voltage of the bridge circuit reflect changes in heating current, which in turn reflects fluid flow.

  • Enclosure and protection: The entire sensor assembly is enclosed in a protective case, which may include an explosion-proof design to adapt to different industrial environments, especially where explosive gases are present.

Thermal gas mass flow meters are widely used in petrochemistry, medicine, food processing, and environmental monitoring due to their characteristics of no need for temperature and pressure compensation, fast response speed, and wide application range. It has been widely used in many fields.

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