If the 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 so how exactly does a calorimetric flow switch actually work? The following blog post explains this in more detail.
Calorimetric flow switches, which are generally generally known 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 that is using the calorimetric measuring principle includes a measuring probe with two temperature sensors integrated into it (see illustration). One of many 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 bigger the flow velocity of the medium in the offing, 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. Insidious 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 which may be heated. In this technical solution, the heating power is regulated so 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 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
Do you have further questions on the measuring principle behind the calorimetric flow switch or do you need help with selecting such a 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.