An introduction to pressure sensors
Piezoresistive technology measures pressure by using the change in electrical resistance of a material when it is stretched. ■ Potentiometric: utilizes a resistance device (potentiometer) and a sliding arm connected to a Bourdon tube. As the pressure changes, the arm moves, and a relative signal is produced by the potentiometer based on the force level. ■ Resonant: force applied to a diaphragm with a vibrating wire alters the resonant frequency of the wire, which is converted into an electrical signal. ■ Strain Gauge: transforms an applied force (pressure) into a change in electrical resistance that fluctuates with the applied force. This resistance can then be measured. Pressure sensor types To understand pressure sensors, it's also important to review the different types available for use in a design. Below are the basic types, presented in alphabetical order: ■ Diaphragm sensors: incorporate thin, flexible, circular metal plates that deform under pressure. ■ Sealed sensors: use atmospheric pressure at sea level as the reference pressure. ■ Solid-state sensors: with no moving parts, these sensors use a semiconductor switching
Figure 1: Visualizing the relationship between the variety of pressure measurements. (Image source: CUI Devices)
between the plates of a capacitor.
Common pressure measurement technologies The origins of pressure detection, comprehension, and measurement can be traced back to the pioneering work of Galileo in the late 1500s and Torricelli in the mid- 1600s. The Bourdon Tube, the first pressure gauge, was invented in 1849, and it wasn't until 1930 that the first electrical output pressure transducers were introduced. With the rise of semiconductor technology, the number of different technologies utilized to detect this fundamental force has surged. Here is a brief overview of the primary pressure measurement technologies and their applications: ■ Capacitive: detects alterations in electrical capacitance caused by pressure flexing a diaphragm
■ Inductive: detects minute deflections of a diaphragm linked to a magnetic core that causes linear motion in the core. This motion varies the induced current and is transformed into an electrical signal. ■ Optical: utilizes a light source that is gradually blocked by an increase in pressure and a sensor that produces a signal proportional to the change in the light. Fiber-optic sensors can also be used to measure changes in the path and phase of light caused by pressure. ■ Piezoelectric: a quartz or ceramic material generates a variable electric charge proportional to the amount of compression applied to it by an external pressure.
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