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Absolute Pressure [ab-sə-ˌlüt pre-shər]

Absolute pressure uses perfect vacuum (the empty space of the universe) as a zero reference. It uses an absolute scale, making it equal to gauge pressure plus atmospheric pressure (on earth at sea level this is 760 Torr). This is commonly seen with the PSIA unit of measurement, meaning pounds per square inch absolute (as opposed to PSIG, or pounds per square inch gauge).

Gauge Pressure [gāj presh-er]

Gauge pressure uses atmospheric pressure (760 Torr on earth at sea level) as a zero reference. This results in the possibility for negative gauge pressures, which can be confusing. Negative gauge pressure means that the system is under vacuum from the perspective of a person accustomed to the earth’s atmosphere. This is commonly seen with the PSIG unit of measurement, meaning pounds per square inch gauge (as opposed to PSIA, or pounds per square inch absolute).

Atmospheric Pressure [at-mə-ˈsfir-ik presh-er]

Atmospheric pressure is also sometimes called barometric pressure. It is the pressure within the earth’s atmosphere, and at sea level, it is defined as 760 Torr. As your altitude increases, atmospheric pressure will decrease and approach perfect vacuum.

Linearity [li-​nē-​ˈer-​ə-​tē]

Generally, linearity can be described as a function that can be represented by a straight line on a graph. A familiar equation for this might be y = mx + b or f(x) = mx + b. For Fredericks sensors, this is defined as the maximum deviation from a linear output as a percentage of the measurement range. This is important because most sensors do not provide a perfectly linear output, and therefore the conversion from the raw sensor output to an accurate physical value can be challenging.

Analog Output [a-nə-ˌlȯg au̇t-ˌpu̇t]

An analog output is a voltage or current output corresponding to a physical input. For Fredericks products, this corresponds to a tilt angle position or a pressure/vacuum measurement, and is typically 0 to 5 V DC, 0 to 10 V DC, or 4 to 20 mA.

Repeatability [ri-​ˌpē-​tə-​ˈbi-​lə-​tē]

The repeatability of a sensor is the maximum deviation in the sensor output from an identical physical input. For example, if you place a tilt sensor at 0° tilt, move it, and return it to 0° tilt, the repeatability is the difference between the original and final outputs.

Rough Vacuum [rəf va-(ˌ)kyüm]

Rough vacuum is typically defined as the absolute pressure range from 760 Torr to 25 Torr.

Medium Vacuum [mē-dē-əm va-(ˌ)kyüm]

Medium vacuum is typically defined as the absolute pressure range from 25 Torr to 1*10^-3 Torr.

High Vacuum [hī va-(ˌ)kyüm]

High vacuum is typically defined as the absolute pressure range from 1*10^-3 Torr to 1*10^-9 Torr.

Ultra-High Vacuum [əl-trə-ˈhī va-(ˌ)kyüm]

Ultra-high vacuum is typically defined as the absolute pressure range from 1*10^-9 Torr to 1*10^-12 Torr.

Extreme High Vacuum (XHV) [ik-ˈstrēm hī va-(ˌ)kyüm]

Ultra-high vacuum is typically defined as the absolute pressure range less than 1*10^-12 Torr.

Perfect Vacuum [pər-fikt va-(ˌ)kyüm]

Perfect vacuum is a theoretical value of 0 Torr. This is essentially a volume containing no matter.

Resolution [re-zə-ˈlü-shən]

The resolution of a sensor is the smallest incremental physical input change that results in a monotonic output (continuously increasing or decreasing depending on the directionality of the physical input).

Operating Range [ä-pə-ˌrā-tiŋ rānj]

The operating range of a sensor is the maximum range over which the physical input produces a monotonic output (continuously increasing or decreasing depending on the directionality of the physical input). It is also the range over which all of the operating specifications stay within their defined tolerances. For example, a sensor may continue to have a monotonic output outside of its operating range, but the output resolution may be decreased.