FAQ`s

What are the different units of pressure and what do they represent?
In the US, the most widely used unit for pressure is the pound per square inch or psi. As its name implies, one psi is equivalent to a force of one pound over an area of one square inch. The SI unit for pressure is the pascal, which is defined as a force of one newton over an area of one square meter. Other units derived from the pascal include the bar, equal to 10,000 pascal, and the standard atmosphere (atm), equal to 101,325 pascal. Another common pressure unit is the torr (closely related to mmHg), which is defined as 1/760 of an atmosphere, and thereby is also indirectly derived from the pascal.

Please visit the conversion table > to compare different units of pressure.

What do extended abbreviations, such as psia or psid, mean?
In each case, the extra letter indicates the reference point for the pressure measurement. Absolute pressure (psia) indicates that the measurement is given relative to a total vacuum. Differential pressure (psid) indicates that the measurement is given relative to some other pressure source. Gauge pressure (psig), or more exactly vented gauge pressure (psivg), means that the measurement is given relative to local pressure. Sealed pressure (psis), or more exactly sealed gauge pressure (psisg), means that the measurement is given relative to some sealed chamber which usually holds standard atmospheric pressure. All these different measurements of pressure are usually a positive number, which indicates that the measured pressure is greater than the reference pressure, and this is always the case for absolute pressure.

What can affect a pressure transducer’s measurements?
Many variables can influence a pressure transducer’s performance characteristics. Set-up conditions related to the pressure medium, fixture tightening, and mating port may also introduce inaccuracies. Additionally, environmental conditions such as temperature, humidity, and electrical noise, as well as high vibrations, extended cycling, and others are able to impact the output signal. For these reasons, it is important to consider all such factors before choosing a pressure transducer, and to contact the manufacturer to ensure that the pressure transducer matches the application.

What are the different performance specifications and what do they mean?
Each specification gives the maximum error range for a given pressure transducer’s output (usually as a percentage of full scale output) in regard to a specific characteristic. There are four main specifications which are critical to understanding pressure transducer performance. First, non-linearity determines how much the output deviates from a perfectly straight line. Second, hysteresis gives the difference between the descending and ascending outputs. Third, repeatability is the measure of how consistently the output repeats from run to run. And fourth, thermal effects show the error in output that occurs as the result of a temperature change. The combined error of all these specifications does not exceed one percent for almost all pressure transducers, and it may be as low as a few hundredths of a percent for the most precise.