Bubble sensor
Bubble sensors are used to detect the presence of bubbles in fluid-filled tubes. They play a vital role in many fields, including medical technology, process control, pharmaceuticals, and the petroleum industry. The most common type of sensors used are ultrasonic or capacitor based.
Ultrasonic sensors
Ultrasonic sensors use two techniques to detect bubbles, one method involves transmitting sound waves from a transducer through the fluid to a second transducer that detects the waves. A second method involves pulse-echo, sound waves are transmitted to the fluid, reflected and received by the same transmitter that sent it. In both of these methods bubbles will have an effect on the velocity, attenuation and the scattering of the sound, thus they are easily detected.Capacitive sensors
Due to their ease of fabrication and minimization capability, Capacitive sensors have found uses in a number of industries and can be efficiently designed on a printed circuit board. A capacitor consist of two parallel electrodes with a capacitance computed as,C =εA/d
Where ε is the permittivity of the dielectric medium, A is the cross sectional area of the electrodes and d is the distance between them. Liquids have a higher dielectric constant than gas; when an air bubble is in a fluid-filled tube the capacitance is reduced and the output voltage rises. The size of the bubble is inversely related to the measured capacitance. Table 1 shows an example of the characteristics of a particular capacitive sensor being researched.
| Capacitance | Air Bubble Diameter | Output Voltage |
| 43.50 | 0 | 18.60 |
| 42.63 | 0.82 | 20.30 |
| 42.54 | 1.00 | 22.01 |
| 41.07 | 2.97 | 40.50 |
| 40.44 | 3.55 | 43.70 |
| 39.38 | 4.00 | 47.90 |
'''Table 1 Example Characteristics of a Particular Capacitive Sensor'''