The Most Commonly Used Manometer Fluids Are Mercury, Oil, Alcohol And Water

　　Air manometer, an instrument used to measure the condition of a fluid (liquid or gas), which is specified by the force applied by the fluid on a unit area (for example, pounds per square inch or Newtons per square centimeter) when the fluid is at rest.

　　The reading on the pressure gauge (that is, the difference between the two pressures) is called the gauge pressure. If the lower pressure is atmospheric pressure, the total pressure or absolute pressure is the sum of gauge pressure and atmospheric pressure.

　　The simplest device for measuring static pressure is about 90 pounds per square inch (62 Newtons per square centimeter) U-tube manometer, where one column of liquid in the tube is an open high-pressure area and the other column Low pressure in the area. The pressure difference is represented by the liquid level difference between the two columns of liquid and is calculated as the liquid level difference multiplied by the liquid density. The most commonly used manometer fluids are mercury, oil, alcohol, and water.

　　This Bourdon tube level gauge was invented in 1850 and is still one of the most widely used instruments for measuring up to 100,000 pounds per square inch (70,000 Newtons per square inch) of various liquids and gases (including steam, water, and air) pressure. Square centimeters). The device (also shown in the picture) consists of a flat circular tube coiled into a circular arc. One end is welded to the center block and communicates with the fluid whose pressure is to be measured; the other end is sealed and coupled to the pointer spindle. When the pressure inside the test tube is greater than the external pressure, the test tube tends to straighten, causing the pointer to rotate. Read the pressure on a circular scale.

　　Metal bellows and diaphragms are also used as pressure sensing elements. Due to the small deflection and large pressure changes, the bellows instrument is particularly suitable for pressures below atmospheric pressure. In an aneroid barometer, two corrugated diaphragms sealed at their edges to form a capsule are used, and these diaphragms are evacuated to measure atmospheric pressure.

　　These instruments use mechanical linkage, so they are mainly used to measure static pressure or slowly changing pressure. For rapidly changing pressure, an electronic pressure sensor that converts the pressure into an electrical signal is more suitable. These include strain gauges; moving contact resistive elements; and inductive, magnetoresistive, capacitive, and piezoelectric devices. Electromechanical sensors used in hydraulic controllers that require speed and power convert changes in fluid pressure into electrical signals.