Pressure Measurements

Barometer

Piezometer

Open-ended tube connected to a vessel / pipe containing a liquid.

Measures the pressure head of a liquid.

Advantages

• Simple
• Small pressure differences can be measured

Disadvantages

• Only for liquids
• Long tube required to measure even moderate pressures

Manometer

Hydrostatic principle is used here. Measures absolute pressure. Manometer liquid should not mix with the liquid in which the pressure is to be measured.

$$P_x = P_y$$ $$P_{A} + a\rho g = P_{\text{atm}} + h \rho_{m} g$$ $$P_{A} = P_{\text{atm}} + h \rho_{m}g - a\rho g$$

Differential Manometer

Used to measure pressure difference between two points. Can be used for both liquids and gases. Difficult to measure small pressure differences (because small displacement of manometer liquid).

Pressure Gauges

Bourdon Pressure Gauge

Advantages

• Easy to use
• Wide range of pressures can be measured

Disadvantages

• Not very accurate
• Needs to be calibrated regularly