Mechanical Pressure Sensors(I)
Date：2016-4-12
Pressure:
Pressure is defined as a force per unit area, and can be measured in units such as psi (pounds per square inch), inches of water, millimeters of mercury, pascal (Pa, or N/m²) or bar. Until the introduction of SI units, the 'bar' was quite common.
The bar is equivalent to 100,000 N/m², which were the SI units for measurement. To simplify the units, the N/m² was adopted with the name of Pascal, abbreviated to Pa.
Pressure is quite commonly measured in kilo pascals (kPa), which is 1000 Pascal and equivalent to 0.145psi.
Absolute, Gauge and Differential Pressure:
Pressure varies depending on altitude above sea level, weather pressure fronts and other conditions. The measure of pressure is, therefore, relative and pressure measurements are stated as either gauge or absolute.
Gauge pressure is the unit we encounter in everyday work (e.g., tire ratings are in gauge pressure). A gauge pressure device will indicate zero pressure when bled down to atmospheric pressure (i.e., gauge pressure is referenced to atmospheric pressure). Gauge pressure is denoted by a (g) at the end of the pressure unit , e.g., kPa (g)
Absolute pressure includes the effect of atmospheric pressure with the gauge pressure. It is denoted by an (a) at the end of the pressure unit, e.g., kPa (a). An absolute pressure indicator would indicate atmospheric pressure when completely vented down to atmosphere - it would not indicate scale zero.
Absolute Pressure = Gauge Pressure + Atmospheric Pressure
The majority of pressure measurements in a plant are gauge. Absolute measurements tend to be used where pressures are below atmosphere. If the gauge is used to measure the difference between two pressures, it then becomes differential pressure.
Mechanical Pressure Sensors:
The object of pressure sensing is to produce a dial indication, control operation or a standard (4 - 20 mA) electronic signal that represents the pressure in a process. To accomplish this, most pressure sensors translate pressure into physical motion that is in proportion to the applied pressure. The most common mechanical pressure sensors or primary pressure elements are :
1) Bourdon tube
2) Helix and spiral tubes
3) Bellows and capsules
4) Diaphragm
5) Spring and piston
Pressure is defined as a force per unit area, and can be measured in units such as psi (pounds per square inch), inches of water, millimeters of mercury, pascal (Pa, or N/m²) or bar. Until the introduction of SI units, the 'bar' was quite common.
The bar is equivalent to 100,000 N/m², which were the SI units for measurement. To simplify the units, the N/m² was adopted with the name of Pascal, abbreviated to Pa.
Pressure is quite commonly measured in kilo pascals (kPa), which is 1000 Pascal and equivalent to 0.145psi.
Absolute, Gauge and Differential Pressure:
Pressure varies depending on altitude above sea level, weather pressure fronts and other conditions. The measure of pressure is, therefore, relative and pressure measurements are stated as either gauge or absolute.
Gauge pressure is the unit we encounter in everyday work (e.g., tire ratings are in gauge pressure). A gauge pressure device will indicate zero pressure when bled down to atmospheric pressure (i.e., gauge pressure is referenced to atmospheric pressure). Gauge pressure is denoted by a (g) at the end of the pressure unit , e.g., kPa (g)
Absolute pressure includes the effect of atmospheric pressure with the gauge pressure. It is denoted by an (a) at the end of the pressure unit, e.g., kPa (a). An absolute pressure indicator would indicate atmospheric pressure when completely vented down to atmosphere - it would not indicate scale zero.
Absolute Pressure = Gauge Pressure + Atmospheric Pressure
The majority of pressure measurements in a plant are gauge. Absolute measurements tend to be used where pressures are below atmosphere. If the gauge is used to measure the difference between two pressures, it then becomes differential pressure.
Mechanical Pressure Sensors:
The object of pressure sensing is to produce a dial indication, control operation or a standard (4 - 20 mA) electronic signal that represents the pressure in a process. To accomplish this, most pressure sensors translate pressure into physical motion that is in proportion to the applied pressure. The most common mechanical pressure sensors or primary pressure elements are :
1) Bourdon tube
2) Helix and spiral tubes
3) Bellows and capsules
4) Diaphragm
5) Spring and piston
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