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 referred to as a flow monitor ? is often used. But how does a calorimetric flow switch really work? The following 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 which is using the calorimetric measuring principle consists of a measuring probe with two temperature sensors integrated into it (see illustration). One of the sensors is heated continuously using a built-in 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 your two sensors, that is registered by the electronics. The bigger the flow velocity of the medium in the offing, the smaller this temperature difference is. The basis for this may be the cooling aftereffect of flowing media. The molecules in the medium, which are flowing at night 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.
Faith 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, 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 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 want 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 be happy to assist you to.

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