Pressure measurement is an important process for many industrial control systems. Many instruments have been invented to measure pressure, with different advantages and disadvantages. Pressure range, sensitivity, dynamic response and cost all vary by several orders of magnitude from one instrument design to the other. Electronic and Hydrostatic gauges are common pressure measurement instruments. Hydrostatic gauges (such as the mercury column manometer) compare pressure to the hydrostatic force per unit area at the base of a column of fluid. Hydrostatic gauge measurements are independent of the type of gas being measured, and can be designed to have a very linear calibration, and have poor dynamic response.

Principal Pressure Measurement Instruments

  • Manometer is a pressure measuring instrument, usually limited to measuring pressures near to atmospheric. The term manometer is often used to refer specifically to liquid column hydrostatic instruments. The various types of manometers are: Simple Manometer, Micromanometer, Differential manometer, and Inverted differential manometer.
  • Vacuum Gauge is used to measure the pressure in a vacuum—which is further divided into two subcategories, high and low vacuum (and sometimes ultra-high vacuum).
  • Piston-type Pressure Gauges counterbalance the pressure of a fluid with a spring (for example tire-pressure gauges of comparatiively low accuracy) or a solid weight, in which case it is known as a deadweight tester and may be used for calibration of other gauges.
  • McLeod Gauge Pressure Measurement – A McLeod gauge isolates a sample of gas and compresses it in a modified mercury manometer until the pressure is a few mmHg.
  • Aneroid Pressure Gauge – Aneroid gauges are based on a metallic pressure sensing element which flexes elastically under the effect of a pressure difference across the element. “Aneroid” means “without fluid”.
  • Bourdon Pressure Gauge – The Bourdon pressure gauge uses the principle that a flattened tube tends to change to a more circular cross-section when pressurized.
  • Bellow Pressure Gauge – Bellows are gauges intended to sense small pressures or pressure differences, or require that an absolute pressure be measured, the gear train and needle may be driven by an enclosed and sealed bellows chamber, called an aneroid, which means “without liquid”.
  • Ionization Pressure Measurement Gauge – Ionization gauges are the most sensitive gauges for very low pressures (also referred to as hard or high vacuum). They sense pressure indirectly by measuring the electrical ions produced when the gas is bombarded with electrons.
  • Pirani Gauge Pressure Measurement System – Pirani (one wire) gauge consists of a metal wire open to the pressure being measured. The wire is heated by a current flowing through it and cooled by the gas surrounding it. If the gas pressure is reduced, the cooling effect will decrease, hence the equilibrium temperature of the wire will increase. The resistance of the wire is a function of its temperature: by measuring the voltage across the wire and the current flowing through it, the resistance (and so the gas pressure) can be determined.
  • Permanent Downhole Pressure Gauge (PDG) is a pressure and/or temperature gauge permanently installed in an oil or gas well. Typically they are installed in tubing in the well and can measure the tubing pressure or annulus pressure or both.
  • Time Pressure Gauge – Time pressure gauge is an instrument that digitally displays pressure data into time intervals. It translates complex pressure data (pounds per square inch or psi) into simplified duration format (time) creating greater precision and efficiency.