Flow sensors are used to measure flow rates and often also the total volume of liquids flowing through a specified cross-section. Flow sensors and flow switches can be used to control both the flow rate and level of liquids in industrial applications. Depending on the application, different flow sensors are used:
Inline Flow Switch
Inline flow sensors operate with a movable magnet in the liquid flow restricting the flow as little as possible, and a fixed reed switch in the sensor housing. The flow in the sensor works against gravity. As soon as the flow exceeds the minimum specified value, it moves the magnet or plunger inside the flow tube, which is made of brass or resin. As the flow continues to increase, this magnet finally closes a magnetic switch in the control circuit and thus actuates the output relay. If the flow drops below the specified value and the plunger returns to its rest position, the output relay remains activated for the set time delay and then will be switched off.
Paddle Flow Switch
Paddle type flow switches are based on paddles that are positioned perpendicular to the flow direction and protrude into the flow. The flow exerts a force which deflects the paddle against a reset resistance as soon as the flow exceeds the specified minimum value, with a deflection angle proportional to the flow velocity. As soon as the flow reaches the nominal value and the paddle deflects accordingly far, a magnet mounted on top of the paddle closes a magnetic switch in the electronics of the flow sensor. If the flow falls below the specified value again, the paddle returns to its rest position and the switch opens. Versions in which all parts in contact with the liquid are made of stainless steel are suitable for measurements in drinking water or aggressive liquids. A choice of paddles allows the flow switches to be adapted to the application.
Ultrasonic Flow Sensors
Flow sensors based on ultrasound technology offer highly accurate and non-invasive flow measurement at a significantly lower cost than other current non-invasive measurement methods. In the in-line measuring cell integrated in these sensors, the flow is measured by determining the ultrasonic transit time in the medium flowing through the cell. The flow path is designed in such a way that the pressure drop is kept to a minimum. Since no moving parts protrude into the flow channel, the risk of the sensors clogging or jamming is very low. Impurities also pass through the sensors without impairing their function. The unique measuring technology automatically compensates for fluctuations in the viscosity or temperature of the measured medium. At the output of the electronics, the user can choose between pulse and analog signals - simply by selecting the appropriate connection cables.