If the presence of flow in a piping system must be monitored, a calorimetric flow switch ? often known as a flow monitor ? is often used. But so how exactly does a calorimetric flow switch really work? The following blog post explains this in more 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 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 in line with the calorimetric measuring principle consists of a measuring probe with two temperature sensors built-into it (see illustration). One of many sensors is heated continuously with the aid of an integrated 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. Successful of the medium in the offing, the smaller 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. The more molecules flow past, the greater the cooling effect. The quantity 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, among and this can be heated. In this technical solution, the heating power is regulated in order 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 in order to keep the size of the temperature difference constant. The applied heating power is thus a primary 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 need help with selecting 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 help you.