Thermal gas flow meters measure mass flow with high accuracy and wide range; thermal flow switches monitor the presence or absence of flow with high sensitivity. Both have different principles, applications and functional characteristics and need to be selected according to requirements.
Thermal gas flow meters and thermal flow switches play an important role in the field of industrial measurement and control. Although they are similar in some respects, there are significant differences in their operating principles, application scenarios and functional characteristics.
Differences in Operating Principles
Both thermal gas flow meters and thermal flow switches operate on the principle of thermal dispersion. Thermal gas flow meters work by heating the sensing element and measuring its heat loss to derive the mass flow rate of the gas. Specifically, the flowmeter contains two internal platinum RTD temperature sensitive elements, one acting as a reference head that senses the temperature of the medium, and the other acting as a measuring head that is partially heated by the circuitry. As the gas flows through the measuring head, it picks up some of the heat, resulting in a temperature difference between the two sensing heads. This temperature difference is converted into a voltage signal by the circuit, which in turn calculates the mass flow rate of the gas. The mass flow rate of a gas has a specific relationship to the temperature difference between the sensing heads and the heating power, and this relationship allows thermal gas flow meters to directly measure the mass flow rate of a gas without the need for temperature and pressure compensation.
In contrast, the operating principle of a thermal flow switch is more focussed on the presence or absence of flow and changes in flow rate. It also contains two platinum RTDs, one of which is heated as a detection resistor and the other unheated as a reference resistor. As the medium flows, heat is removed from the heated resistors, the resistance changes and the difference between the two resistors is used as a basis for determining the flow rate. Once the flow rate reaches or exceeds the preset threshold, the flow switch will issue an alarm or control signal, thus realising the monitoring and control of the flow rate.
Differences in application scenarios
Thermal gas flow meters are widely used in several industrial fields for their high accuracy, wide range ratio and direct mass flow measurement. For example, in the power industry, accurate measurement and control of combustion air flow in boilers is essential for improving combustion efficiency, reducing flue gas emissions and lowering energy consumption. Thermal gas flowmeters reliably measure the mass flow of combustion air to help achieve optimal combustion ratios. In addition, thermal gas flow meters play an important role in flue gas emission monitoring systems by accurately measuring the flow rate of the flue gas being discharged, providing a reliable basis for the correct calculation of the total emissions.
Thermal flow switches are more often used for the control and monitoring of liquid and gas flows, especially in scenarios where the presence of a flow or the flow rate reaching a specific value needs to be monitored. For example, in pneumatic and hydraulic systems, thermal flow switches can be used to monitor the flow of circulating water, cutting fluids and lubricating oils, as well as to protect pumps from idling. When the flow rate falls below a set value, the flow switch signals an alarm, alerting the operator to take action in time to prevent equipment damage or production interruption. In addition, thermal flow switches are often used in industrial processes for overflow protection and equipment failure signalling and other scenarios, providing a strong guarantee for the safe and stable operation of industrial production.
Comparison of functional characteristics
In terms of functional characteristics, thermal gas flow meters and thermal flow switches also have their own distinctive features. Thermal gas flowmeter has a wide range ratio, good seismic performance, long service life, high degree of digitalisation and a variety of communication interfaces. It is capable of measuring gases with a wide range of flow rates, from as low as 0.1Nm/s to as high as 120Nm/s, and is suitable for gas flow measurement in various complex environments. At the same time, its sensor has no moving parts and pressure sensing parts, and is not affected by vibration on the measurement accuracy, with superior anti-vibration performance. The digital design enables accurate measurement and easy maintenance, while the multiple communication interfaces realise the needs of factory automation and integration.
Thermal flow switches are known for their high sensitivity, unlimited installation locations, different materials to suit different acidic and alkaline liquid environments, customisable length of flow sensing rods, and a variety of signal output methods. It can be accurately and easily adjusted configuration, work reliably, easy to operate, especially suitable for impurity-containing liquid flow control and monitoring. In addition, thermal flow switches are compact, easy to install, and explosion-proof for hazardous locations, further broadening their application scenarios.
Choices for real-world applications
In practical applications, the choice of thermal gas flow meter or thermal flow switch needs to be based on specific measurement needs, working environment and cost control and other factors for comprehensive consideration. If you need to measure the mass flow rate of gas, and have high requirements for measurement accuracy and range ratio, then the thermal gas flow meter is a better choice. It can directly measure the mass flow rate of gases without temperature and pressure compensation, and with high measurement accuracy and wide range ratio, it is suitable for gas flow measurement in various complex environments.
If only the presence or absence of flow or whether the flow rate reaches a specific value is required, and the requirements for measurement accuracy and range ratio are relatively low, then a thermal flow switch may be more appropriate. It can sensitively sense changes in flow rate and issue an alarm or control signal when the flow rate reaches or exceeds a preset threshold, providing a strong guarantee for the safe and stable operation of industrial production. At the same time, the thermal flow switch also has the advantages of easy installation, low maintenance cost and applicability to a variety of fluid media, which further improves its competitiveness in practical applications.
In summary, thermal gas flowmeter and thermal flow switch in the working principle, application scenarios and functional characteristics of the significant differences. In practical applications, we need to consider the specific measurement needs, working environment and cost control and other factors to choose the most suitable measurement tool. Only in this way, we can better play the advantages of these devices, for the safe, stable and efficient operation of industrial production to provide strong support.
Hangzhou Economic Development Area，Hangzhou 310018，China
