If the current presence of flow in a piping system must be monitored, a calorimetric flow switch ? generally known as a flow monitor ? is often used. But how does a calorimetric flow switch really 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 in line with the calorimetric measuring principle consists of a measuring probe with two temperature sensors integrated into it (see illustration). Among the 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 second 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, the smaller this temperature difference is. The basis for this is the cooling effect of flowing media. The molecules in the medium, which are flowing at night probe tip, collect ?packages of heat? and transport them away. The more molecules flow past, the higher the cooling effect. The number 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 which can be heated. In this technical solution, the heating power is regulated so 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 how big is the temperature difference constant. The applied heating power is thus a direct 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 the selection of such a product? In its portfolio, WIKA has a calorimetric flow switch for monitoring the flow of liquid media (model FSD-3). Beating will undoubtedly be happy to assist you to.