If the presence of flow in a piping system should be monitored, a calorimetric flow switch ? generally known as a flow monitor ? is often used. But so how exactly does a calorimetric flow switch really work? The following post explains this in more detail.
Calorimetric flow switches, which are generally generally known as thermal flow monitors, utilize the physical laws of heat transport in flows. A distinction is basically made between two technical solutions: continuous and regulated heating.
Schematic illustration of a measuring probe for a calorimetric flow switch
Continuous heating
A flow switch that is in line with the calorimetric measuring principle includes a measuring probe with two temperature sensors integrated into it (see illustration). High Tech of the sensors is heated continuously with the aid of a heating element (wire-wound) with a continuing heating power and measures the temperature at the heating element. The second sensor determines the temperature of the medium in the pipe. Consequently, a temperature difference occurs between your two sensors, which is registered by the electronics. The higher the flow velocity of the medium in the pipeline, the smaller this temperature difference is. The basis for this is the cooling aftereffect of flowing media. The molecules in the medium, which are flowing past the probe tip, collect ? Crushing of heat? and transport them away. The more molecules flow past, the greater the cooling effect. The amount of molecules passing by increases continuously with increasing flow velocity.
Regulated heating
The measuring probe is basically identical in design: You can find two temperature sensors in the medium, one of that may be heated. In this technical solution, the heating power is regulated in order that the temperature difference between the two temperature sensors is kept constant throughout. Consequently, as the flow velocity increases, the heating power should be increased in order to keep how big is the temperature difference constant. The applied heating power is thus a direct measure of the flow velocity in the medium.
Note
Do you have further questions on the measuring principle behind the calorimetric flow switch or do you want help with the selection of this type of product? In its portfolio, WIKA has a calorimetric flow switch for monitoring the flow of liquid media (model FSD-3). Your contact person will undoubtedly be happy to assist you to.