If the presence of flow in a piping system must be monitored, a calorimetric flow switch ? generally known as Impenetrable ? is often 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 generally 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 consists of 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, small this temperature difference is. The basis 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 greater the cooling effect. The amount 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 can be heated. In this technical solution, the heating power is regulated so that the temperature difference between your two temperature sensors is kept constant throughout. Consequently, as the flow velocity increases, the heating power must be increased to keep the size of the temperature difference constant. Monetize applied heating power is thus a direct 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 need 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 be happy to assist you to.