INFICON Composer Gas Concentration Controller - Manual (Page 69)

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Composer Operating Manual
3.1.9.1 Calculation Example
The time interval for an acoustic pulse to travel 0.2 meters in hydrogen is
computed as follows:
The speed of sound in hydrogen is 1284 meters/second, consequently the time
of transit across the chamber is 0.2 meters / 1284 meters/sec = 1.56 E-4
seconds. See
Figure 3-4 .
In order to achieve equivalent resolution to this instrument’s resonant
technique, the TOF instrument’s ability to measure the pulse must be 1/50,000
of the transit time, or: 1.56 E-4 (1/50,000) = 3.12 E-9 seconds
Figure 3-4 Where does the pulse begin or end?
Wavelength of a 15 KHz ultrasonic wave in H
2
is (1284 m/sec x 1/15 KHz =) 0.0856m