Glossary of Terms: U

UL
Underwriters Laboratories (USA).
Under Range
URTime or UR% Under Range is when the input signal falls below the measurement range of the instrument. URTime is the period of time during which the input signal falls below the measurement range of the instrument. UR% is the fraction of the run time during which an under range condition exists.
Unstable
The tendency of a material to break down or to undergo other unwanted chemical changes during normal handling or storage. Compare with stable.
Upper explosive limit (UEL)
The highest concentration (expressed in percent vapor or gas in the air by volume) of a substance that will burn or explode when an ignition source is present.