INFICON Composer Elite Gas Concentration Monitor - 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
= =