If the presence of flow in a piping system must be monitored, a calorimetric flow switch ? also referred to as a flow monitor ? is frequently used. But how 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 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 that is based on the calorimetric measuring principle includes 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. The second sensor determines the temperature of the medium in the pipe. Consequently, a temperature difference occurs between the two sensors, that is registered by the electronics. The higher 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 at night 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: You can find two temperature sensors in the medium, among which can be heated. In Focus , 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 must be increased in order to keep how big is the temperature difference constant. Devoted 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 undoubtedly be happy to help you.