Glossary of Oxygen & Industrial Gas Terms

Explore common terms used in oxygen, carbon dioxide (CO₂), hydrogen sulfide (H₂S) and industrial gas analysis. This glossary provides practical definitions for measurement terminology, analyzer specifications, sensor technology, calibration, sample handling and instrumentation.

Term	Definition
ACCURACY	The quality of closeness to a specified value under stated conditions. Usually expressed as uncertainty – the maximum deviation to be expected between a reading or output and the actual value being measured.
AMBIENT AIR	Often used as a term when referencing oxygen analyzer calibration. Ambient air consists of 20.9% oxygen which can be used as a known SPAN gas value.
AMBIENT TEMPERATURE	The minimum / maximum temperature of air surrounding the device or equipment. A critical parameter when specifying an analyzer.
ANALOG	A parameter which varies in a continuous, rather than incremental or discrete-step manner.
CALIBRATE	To determine the indication or output of a device with respect to a standard. 0 through 9, a 1/2 digit will display a 0 or 1 and overrange at 2, a 3/4 digit will display up to 3 and overrange at 4. A meter with a display span of ±3999 counts is a 33/4 digit meter.
EMI / RFI	Electromagnetic interference / Radio Frequency Interference.
EXPANDED SCALE	AAn arrangement that expands a specific portion of an overall range to occupy a larger portion of the full-scale length than it normally would.
EXPLOSION PROOF	An enclosure capable of withstanding an explosion of a specified gas or vapor which may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosures by sparks, flashes, heat or explosion of the gas vapor within.
FORM	A method for specifying relay contact configuration: Form A SPST-NO single pole, single throw, normally open Form B SPST-NC single pole, single throw, normally closed Form C SPDT single pole, double throw Change-Over CO same as SPDT
FULL SCALE VALUE	The arithmetic sum of the two end-scale values (may not apply to some specialized meters, such as power factor). When zero is not on the scale, the full-scale value is the higher end-scale value. Examples: Scale Full Scale Value 0-10 ppm, 0 – 100ppm, 0 – 500ppm, 0 – 1000ppm, 0 – 2500ppm, 0 – 10000ppm, 0 – 1%, 0 – 5%, 0 – 10%, 0 – 25%
GROUND	Reference point for an electrical system. Often used to indicate an earth connection or negative side of a DC supply.
LINEARITY ERROR	A measure of the departure from a straight-line response in the relationship between two quantities, where the change in one quantity is directly proportional to a change in the other quantity. Usually expressed as a maximum percent.
NEMA 4X / IP66 ENCLOSURE	A rating standard which defines intended use and degree of environmental protection. Typically associated with analyzers that will be installed outdoors.
PPM (PARTS PER MILLION)	A convenient format to express very small numbers, such as temperature coefficients. 100ppm is 0.01%. PPM is also written as “trace” as in trace oxygen.
PSIA (PSI Absolute)	A pressure reading using vacuum as the reference.
PSIG (PSI Gauge)	A pressure reading using ambient air pressure as the reference.
RANGE	The span of values over which a meter will function without entering overload condition, e.g. 0-100ppm
REPEATABILITY	The ability of an instrument to register the same reading in successive measurements of the same input.
RESOLUTION	The degree to which nearly equal values of a quantity can be discriminated. In digital meters, the value represented by a one-digit change in the least-significant digit.
SENSITIVITY	The minimum change in input to which a device can respond.
SHIELD	A protective conductive covering that provides a least resistance path to ground for external interference.
SPAN CAL ADJUSTMENT	The ability to adjust the gain of an instrument so the display value.
T90 RESPONSE TIME	The time required for a sensor to respond to 90% of its total change resulting from a step input.
TWO-WIRE TRANSMITTER	An instrument configuration in which the signal output and power input share two wires, power is transfer on one wire and returned to a PLC or DCS system via a 4 – 20mA signal on the other wire. In most cases, this signal is non-isolated.
ZERO CAL ADJUSTMENT	The ability to adjust an instrument so that zero output or zero display corresponds to a specific input signal, such as 0V or 4mA.

Definitions