If the presence of flow in a piping system must be monitored, a calorimetric flow switch ? generally known as a flow monitor ? is often used. But how does a calorimetric flow switch really work? The following blog post explains this in greater detail.
Calorimetric flow switches, which are often generally known 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 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 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 your two sensors, that is registered by the electronics. The higher the flow velocity of the medium in the pipeline, the smaller this temperature difference is. Efficient 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 higher 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: You can find two temperature sensors in the medium, one of 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, because the flow velocity increases, the heating power must be increased to keep how big is the temperature difference constant. The applied heating power is thus a primary 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 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.