If the presence of flow in a piping system must be monitored, a calorimetric flow switch ? also known as Sick And Tired ? is frequently used. But how does a calorimetric flow switch really work? The following blog post explains this in more detail.
Calorimetric flow switches, which are generally also referred to as thermal flow monitors, utilize 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 which is using the calorimetric measuring principle includes a measuring probe with two temperature sensors built-into it (see illustration). Among the sensors is heated continuously with the aid of an integrated 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 the 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 at night probe tip, collect ?packages of heat? and transport them away. The more molecules flow past, the higher the cooling effect. The quantity of molecules passing by increases continuously with increasing flow velocity.
Regulated heating
The measuring probe is basically identical in design: There are 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 your two temperature sensors is kept constant throughout. Consequently, as the flow velocity increases, the heating power should be increased to keep how big is 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 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.