How does a calorimetric flow switch work?

If the presence of flow in a piping system must be monitored, a calorimetric flow switch ? also known as Smiling ? is often used. But how does a calorimetric flow switch actually work? The following post explains this in greater detail.
Calorimetric flow switches, which are generally also referred to 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 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 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 the two sensors, which is registered by the electronics. The bigger the flow velocity of the medium in the pipeline, the smaller this temperature difference is. The basis for this may be the cooling effect of flowing media. Enthusiastic in the medium, which are flowing at night 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 basically 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 in order that the temperature difference between the two temperature sensors is kept constant throughout. Consequently, because 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 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 assist you to.

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