Model 979 Series Helium Mass Spectrometer Leak Detector
C-2
DRAFT 9/15/03
C.3 Terminology
The following terminology has application throughout this manual:
Flow
std cc/sec
One cubic centimeter of gas per second at a pressure differential of
one standard atmosphere (760 torr at 0 °C).
atm cc/sec
One cubic centimeter of gas per second at ambient atmospheric
pressure and temperature (used interchangeably with std cc/sec
because the difference is insignificant for leak testing purposes).
Rate-of-Rise
In vacuum systems, this is defined as the rate of increase of abso-
lute pressure per unit time with the vacuum pump isolated from the
system, and is the sum of actual inleakage and internal outgassing.
Rate of rise is usually expressed in torr or microns (millitorr) per
hour. The flow rate should be expressed in torr-liters/second.
Conversions
1 std cc/sec*0.76 torr-liter/sec
1 torr-liter sec*1.3 std cc/sec
1 atm cc/sec9.7 x 10
4
micron cubic feet per hour or practically
10
5
micron CFH (
µ
CFH)
1
µ
CFH or practically 10
−
5
std cc/sec
*for practical purposes, equal
Numerical Notation,
Exponential System
Most leak rates of commercial significance are very small fractions
of an std cc/sec. Therefore negative powers of ten are used as a
convenient system of numerical shorthand.
Table C-1 shows the relationship of exponents and multipliers (to the base 10) to the
arithmetic form, and the equivalent result.
Table C-1
Decimal Notation
Multiplier x 10
n
Arithmetic Form
Result
1 x 10
2
=
1 x 10 x 10
=
100
1 x 10
1
=
1 x 10
=
10
1 x 10
o
=
1
=
1
1 x 10
−
1
=
1 x 1/10
=
.1
1 x 10
−
2
=
1 x 1/10 x 1/10
=
.01
5 x 10
−
3
=
5 x 1/10 x 1/10 x 1/10
=
.005
1 x 10
−
3
=
1 x 1/10 x 1/10 x 1/10
=
.001
Summary of Contents for 979 Series
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