If the current 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 post explains this in greater 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 in line with 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 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 bigger the flow velocity of the medium in the pipeline, the smaller this temperature difference is. The foundation for this is the cooling effect of flowing media. The molecules in the medium, which are flowing past the probe tip, collect ? เพรสเชอร์เกจ of heat? and transport them away. The more molecules flow past, the higher the cooling effect. The amount 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, one of that 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 should 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
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 includes a calorimetric flow switch for monitoring the flow of liquid media (model FSD-3). Your contact person will undoubtedly be happy to assist you to.