If the presence of flow in a piping system should be monitored, a calorimetric flow switch ? often known as Ingredients ? is frequently 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, use the physical laws of heat transport in flows. A distinction is actually made between two technical solutions: continuous and regulated heating.
Budget of a measuring probe for a calorimetric flow switch
Continuous heating
A flow switch which is based on 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 with the aid of a 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 the two sensors, which is registered by the electronics. The bigger the flow velocity of the medium in the offing, the smaller this temperature difference is. The foundation for this may be the cooling effect 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 amount of molecules passing by increases continuously with increasing flow velocity.
Regulated heating
The measuring probe is actually identical in design: There are two temperature sensors in the medium, among and this can be heated. In this technical solution, the heating power is regulated so that the temperature difference between the two temperature sensors is kept constant throughout. Consequently, as 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 want help with selecting this type of 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.