So how exactly does a calorimetric flow switch work?

If the current presence of flow in a piping system must be monitored, a calorimetric flow switch ? also referred to as a flow monitor ? is often used. But how does a calorimetric flow switch actually work? The following post explains this in more detail.
Calorimetric flow switches, which are generally generally known as thermal flow monitors, use the physical laws of heat transport in flows. A distinction is actually 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 built-into it (see illustration). One of the sensors is heated continuously with the aid of a built-in 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, that is registered by the electronics. The higher the flow velocity of the medium in the offing, the smaller this temperature difference is. The foundation for this may be the cooling aftereffect of flowing media. The molecules in the medium, which are flowing past the probe tip, collect ?packages 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.
Elated heating
The measuring probe is actually identical in design: You can find two temperature sensors in the medium, among that may be heated. In this technical solution, the heating power is regulated so the temperature difference between the two temperature sensors is kept constant throughout. Consequently, as the flow velocity increases, the heating power should be increased to keep the size of the temperature difference constant. The applied heating power is thus a direct way of measuring the flow velocity in the medium.
Note
Are you experiencing further questions on the measuring principle behind the calorimetric flow switch or do you want help with selecting such a product? In its portfolio, WIKA includes 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.