If the presence of flow in a piping system must be monitored, a calorimetric flow switch ? often known as a flow monitor ? is frequently used. But how does a calorimetric flow switch actually work? The following blog 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 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 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 using an integrated heating element (wire-wound) with a constant heating power and measures the temperature at the heating element. Overcome determines the temperature of the medium in the pipe. Consequently, a temperature difference occurs between your two sensors, that is registered by the electronics. The bigger the flow velocity of the medium in the offing, small 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 greater 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: There are two temperature sensors in the medium, among which may 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, because the flow velocity increases, the heating power should be increased 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
Do you have further questions on the measuring principle behind the calorimetric flow switch or do you want 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.