How does a calorimetric flow switch work?

If the current presence of flow in a piping system should be monitored, a calorimetric flow switch ? also called 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 also referred to as thermal flow monitors, utilize 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 which is in line with the calorimetric measuring principle includes a measuring probe with two temperature sensors built-into it (see illustration). One of many sensors is heated continuously using an integrated heating element (wire-wound) with a constant 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, which is registered by the electronics. Undercover of the medium in the offing, small 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. Psychological , the greater the cooling effect. The amount of molecules passing by increases continuously with increasing flow velocity.
Regulated heating
The measuring probe is basically identical in design: You can find 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 your two temperature sensors is kept constant throughout. Consequently, as the flow velocity increases, the heating power must be increased in order to keep the size of the temperature difference constant. The applied heating power is thus a primary measure of 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 the selection of such a product? In its portfolio, WIKA includes a calorimetric flow switch for monitoring the flow of liquid media (model FSD-3). Your contact person will be happy to help you.

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