990 CLD Autoline™ Leak Detector
DR
AFT 2/2/04
6-7
Glossary of Terms
Absolute Pressure
An engineering term to indicate pressure above the absolute zero
corresponding to empty space as distinguished from
gauge
pressure
In vacuum technology, pressure is always absolute pressure, and
therefore the term
absolute pressure
is redundant.
Absorption
The binding of gas in the interior of a solid (or liquid)
Adsorption
The condensing of gas on the surface of a solid.
Atmospheric Pressure
The pressure of the atmosphere at a specified place and time.
The standard atmosphere, or normal atmosphere, is defined
(independently of barometric height) as a pressure of
1,013,250 dyne/cm
2
.
Audible Leak Indicator An auxiliary component of a leak detector, which converts the
output signal to an audible note whose frequency is a function of
the leak size.
Background
An output signal of the leak detector due to entrapment of the
tracer gas or other substance to which the detecting element
responds in the vacuum system, which cannot be quickly removed
by pumping. A virtual leak of the tracer gas.
Background Signal
The steady or fluctuating output signal of the leak detector caused
by the presence or residual tracer gas or other substance to which
the detecting element responds.
Bake-Out
The degassing of a vacuum system by heating during the pumping
process.
Bomb Test
A form of leak test in which enclosures are pressurized with tracer
gas for the purpose of driving through possible leak passages and
thus into the internal cavities. Subsequent leak testing is done by
evacuation or immersion. See “Helium Bombing” below.
Bubble Test
A form of leak testing gas–containing enclosures in which a leak is
indicated by the formation of a bubble at the site of a leak.
Calibrated Leak
An orifice or membrane through which an accurately known
amount of helium passes in a given amount of time The leak is
usually accompanied by a reservoir of helium.
Cold Trap
A vessel designed to hold a refrigerant and which, when inserted
into a vacuum system, traps on its surface condensable vapors
present in the vacuum system. Most traps operate with liquid
nitrogen at a temperature of
−
196 °C (
−
320 °F).
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