How does a Thermal Flow Switch Work?
Thermal flow switches consist of two temperature sensors, power supply, signal processor, and output relay or NPN/PNP transistor output. This type of temperature sensor is made of special semiconductors. The two sensors have very similar physical characteristics and are separated by a certain distance, and the thermal influence between them can be ignored. The sensors are paired to track the temperature of the medium. The voltage drop of these sensors is proportional to the temperature and they work accurately over a wide temperature range. One of the sensors (Sensor1) is heated to a temperature higher than the medium temperature. The other sensor (Sensor2) is at the same temperature as the medium and is called the reference sensor.
The voltage difference generated by the equal constant current flowing through the two sensors is inversely proportional to the amount of heat absorbed and removed by the medium on Sensor1. Since the flow rate of the medium is proportional to the amount of heat removed. By measuring the voltage difference between the two sensors, the flow rate of the medium at this time can be known, and the flow rate of the medium can be known by calculation.
Thermal flow switches are mostly used in cooling circulation systems and lubrication systems.
Thermal flow switches are designed based on the principle of generating a difference in probe temperature changes. A heating sensor and two heat-sensitive sensors are built into the probe and are in contact with the medium. When the thermal flow switch is working, the heating sensor emits a constant amount of heat.
When there is no medium flowing in the pipeline, the heat received by the heat-sensitive sensor is a constant value. When there is medium flowing, the heat received by the heat-sensitive sensor will change with the flow rate of the medium. The thermal sensor converts this temperature difference signal into an electrical signal. When the flow rate reaches a certain set point, the thermal flow switch outputs a switch signal.
What is the Purpose of a Flow Switch?
The function of a flow switch is to trigger a signal according to the change in fluid flow. The flow switch controls or protects the operation of the system to avoid equipment damage or safety accidents.
A flow switch is a device used to monitor the flow of liquids, gases and other media in a pipeline. Its core function is to trigger system actions through flow changes. The specific functions and application scenarios are as follows:
- Protect the safe operation of the equipment
Prevent dry burning: In systems such as boilers and heat pumps, when the water flow rate is lower than the set value (such as 1L/min), the flow switch will output a “break” signal. It prevents dry burning damage to the equipment due to lack of water.
Avoid idling or overload: In industrial pipelines, abnormal flow (too high or too low) may cause damage to the pump or motor. The flow switch can cut off the circuit or adjust the equipment status in time.
- Automation control and alarm
Trigger linkage control: For example, in the fire protection system, when the sprinkler head is started or the fire hydrant is opened, the flow switch detects an increase in flow. The fire pump group is automatically started to ensure water supply.
Alarm function: When the pipeline is broken, blocked or the medium flow exceeds the preset range, the flow switch will send an alarm signal. Prompt the operator to intervene.
- Adapt to different media and scenarios
Multi-media monitoring: Applicable to water, oil, steam, gas, etc., and monitoring is achieved through mechanical baffles, thermal conductivity or ultrasonic principles.
Special environment application: For example, explosion-proof flow switches are used in flammable and explosive environments, and fire-fighting special models meet high temperature and high pressure requirements.
- Energy saving and efficiency optimization
Start and stop equipment on demand: For example, in a circulating water system, the flow switch can control the operation of the water pump according to actual needs.
Precise flow management: Dynamic flow adjustment is achieved through analog output (such as 4-20mA) to improve process stability.
Summary: The core value of flow switches is to ensure system safety and improve automation level through real-time flow monitoring, and they are widely used in industries, fire protection, energy and other fields. Their specific functions need to be comprehensively designed in combination with system types (such as boilers, fire protection pipe networks) and medium characteristics (liquid/gas).
