If the presence of flow in a piping system should be monitored, a calorimetric flow switch ? also referred to as Ordeal ? is often used. But so how exactly does a calorimetric flow switch really work? The following post explains this in greater detail.
Calorimetric flow switches, which are generally also referred to 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 which is based on the calorimetric measuring principle includes a measuring probe with two temperature sensors integrated into it (see illustration). One of the sensors is heated continuously using a heating element (wire-wound) with a constant heating power and measures the temperature at the heating element. The next sensor 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 higher the flow velocity of the medium in the pipeline, small this temperature difference is. The foundation for this is the cooling effect 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.
Regulated heating
The measuring probe is actually identical in design: There are two temperature sensors in the medium, among which is often heated. In this technical solution, the heating power is regulated so the temperature difference between the two temperature sensors is kept constant throughout. Consequently, because 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 primary way of measuring the flow velocity in the medium.
Note
Do you have 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 help you.