If the presence of flow in a piping system should be monitored, a calorimetric flow switch ? also known as a flow monitor ? is frequently used. But so how exactly does a calorimetric flow switch actually work? The following post explains this in greater detail.
Calorimetric flow switches, which are often generally known as thermal flow monitors, use 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 consists of a measuring probe with two temperature sensors built-into it (see illustration). Among the sensors is heated continuously using an integrated heating element (wire-wound) with a continuing heating power and measures the temperature at the heating element. Convenient determines the temperature of the medium in the pipe. Consequently, a temperature difference occurs between the two sensors, which is registered by the electronics. The bigger the flow velocity of the medium in the pipeline, 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 quantity of molecules passing by increases continuously with increasing flow velocity.
Regulated heating
The measuring probe is actually identical in design: There are two temperature sensors in the medium, among which can 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, because 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 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 need help with selecting such a 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.