INFICON Composer Gas Concentration Controller - Manual (Page 44)

2 - 2
IP
N 07
4-
28
9L
Composer Operating Manual
[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]
Where f and f
2
are the resonant frequencies of the mixture and pure gas,
respectively.
f
C
2L
------- =
m
M
1
M
2
-------- =
g
γ
1
γ
2
----- =
h
1
γ
2
----- =
M M
2
m 1 – ( )x 1 + { } =
γ 1 =
γ
2
g h – ( ) 1 h – ( ) { }
x 1 g – ( ) g h – ( ) + { }
-------------------------------------------------- +
C
2
γ
2
RT
M
2
------------- =
c
2
c
2
2
h
g h – ( ) 1 h – ( )
x 1 g – ( ) g h – ( ) +
------------------------------------------- +
 
  1 m 1
– ( )x + [ ] 1 –
=
λ
C
C
2
------
 
 
2
f
f
2
----
 
 
2
= =