If the presence of flow in a piping system should be monitored, a calorimetric flow switch ? also called a flow monitor ? is often used. But how does a calorimetric flow switch actually work? The following blog post explains this in more 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 includes a measuring probe with two temperature sensors built-into it (see illustration). Among the sensors is heated continuously using a built-in heating element (wire-wound) with a continuing 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 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 ?packages of heat? and transport them away. The more molecules flow past, the greater the cooling effect. The number of molecules passing by increases continuously with increasing flow velocity.
Regulated heating
The measuring probe is actually identical in design: You can find two temperature sensors in the medium, one of which 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 Impressive , the heating power must 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 selecting this type of 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 help you.