IFM Efector flow sensors and transmitters are solid state alternatives to mechanical flow switches for sensing the flow rate of liquids and gases. Because there are no moving parts to jam or break, ifm efector flow sensors eliminate the maintenance headaches of mechanical flow switches. ifm efector flow sensors offer a variety of process connections to fit most applications. This flexibility allows the sensor to be easily installed in many different applications that have various mounting requirements.

SI Series Calorimetric Principle

The operating principle of ifm efector flow sensors is based on the calorimetric principle. ifm efector flow sensors use the cooling effect of a flowing fluid or gas to monitor the flow rate. The amount of thermal energy that is removed from the tip determines the local flow rate. This temperature-based operating principle can reliably sense the flow of virtually any liquid or gas.

SI Tip Design

The sensor tip of the SI flow sensor houses two transistors and a heater element. One transistor is located in the sensor tip, closest to the flowing fluid. This transistor is used to detect changes in the flow velocity of the liquid or gas. The second transistor is bonded to the cylindrical wall and is affected only by changes in the temperature of the liquid or gas. 

In order to make the sensor sense flow, it is necessary to heat one of the transistors in the probe. When power is applied, the tip of the probe is heated. As the fluid starts to flow, heat will be carried away from the sensor tip. Cooling of the first transistor is a function of how fast heat is conducted away by the flowing liquid. The difference in temperature between the two transistors provides a measurement of fluid velocity past the sensor probe. When fluid velocity is high, the temperature differential is small. As fluid velocity decreases, there is an increase in temperature differential.

Specifications