INFICON Composer Elite Gas Concentration Monitor User Manual
Page 136
9 - 2
PN
07
4-
56
6-
P1
B
Composer Elite Operating Manual
Composer Elite determines the speed of sound by precisely determining the gases’
fundamental resonant frequency in a fixed chamber of length
L
. At resonance, a
standing half wave exists in the Resonant Chamber, so the speed of sound and
frequency are related as follows:
[6]
In practice, the exact value of
L
is unimportant. Composition is computed from
knowledge of the mixture's frequency relative to the frequency of the pure gas as
follows. Let:
[7]
[8]
[9]
Applying equations 7, 8, and 9 into equations 3 and 4 yields,
[10]
[11]
If we define the speed of sound in the majority, or carrier, gas as
C
2
[12]
and apply equations 9 and 10 into equation 4 we get:
[13]
Since the speed of sound in a fixed resonator is directly proportional to the
frequency of resonance, we define a ratio:
[14]
f
C
2L
-------
=
m
M
1
M
2
--------
=
g
1
2
-----
=
h
1
2
-----
=
M
M
2
m 1
–
x 1
+
=
1
=
2
g h
–
1 h
–
x 1 g
–
g h
–
+
--------------------------------------------------
+
C
2
2
RT
M
2
-------------
=
c
2
c
2
2
h
g h
–
1 h
–
x 1 g
–
g h
–
+
-------------------------------------------
+
1 m 1
–
x
+
1
–
=
C
C
2
------
2
f
f
2
----
2
=
=