Different types of pressure from different sources must be measured, um, differently. As such, there are a plethora of different instruments for measuring pressure. You’ve likely seen more than a few of them in your everyday life: tire gauges, blood pressure meters (which are technically called sphygmomanometers), etc. But, what makes these instruments different?Let’s take a look at some common pressure gauges and how they work.
Liquid Column Gauges
Wherever gravity is present (i.e. anywhere except a vacuum), a liquid column gauge can be used to measure pressure. A simple example uses a U-shaped tube half filled with liquid—one end is connected to the source of the pressure on wishes to measure, while the other end has reference pressure applied (usually ambient atmospheric pressure). The liquid column inside the tube will rise and fall until it reaches a pressure equilibrium between the two sources. Markings on the side of the tube note the level of pressure reached.
Bourdon pressure gauges utilize flattened tubes, bent into a C or helix shapes, that straighten when pressurized. One end of the flattened tube is attached to the pressure source, while the other is attached to a mechanical device that serves as the actual gauge. As the tube straightens out, it move the needle portion of the device across the numbered face of the gauge, indicating the level of pressure.
The pressure of the fluid/gas being measured is counterbalanced by a spring or solid weight. Piston-type gauges are often used to calibrate other types of pressure gauges.
These pressure instruments compare pressure to the hydrostatic force per unit area at the base of a column of fluid. Measurements from these gauges remain consistent regardless of the type of fluid or gas being measures.
These electronic pressure gauges measure the electrical ions produced by a gas as it is bombarded by electrons. Ionization gauges provide indirect measurement and are difficult to calibrate, as they are dependent on the nature of the gas being measured.