milk, and liquid styrene, lasers operate on a principle very similar to that of ultrasonic level sensors. Instead of using the speed of sound to find the level, however, they use the speed of light (see Figure 9). A laser transmitter at the top of a vessel fires a short pulse of lig...
As the flow passes through the chamber, the displacer piston is moved downstream. Dividing the volume of the chamber by the time it takes for the displacer to move from one detector to the other gives the calibrated flow rate. This rate is then compared to the reading of the flow meter ...