INFICON Composer Elite Gas Concentration Monitor - Manual (Page 61)

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Composer Elite Operating Manual
4.1.7 What is the Effect of Flow Variation?
There is virtually no flow induced effect on concentration measurement in the
Composer Elite System except at the highest flow rates, see
Figure 4-3 , the
pressure drop across the Acoustic Sensor is about 12 Torr [1.60 kPa] at 2000 sccm
for the Standard sensor or 6 Torr [0.80 kPa] for the High Flow sensor.
HINT: Large variations in flow rate will cause a shift in the zero concentration
point. To minimize zero shift due to flow rate change, carefully set the inlet
tubing heater temperature (Temperature Setpoint 2). The default value for
Temperature Setpoint 2 is 3 degrees higher than Temperature Setpoint 1.
Adjusting the Temperature Setpoint 2 value slightly might be necessary
depending on your process requirements.
Figure 4-3 Effect of flow on apparent concentration
4.1.8 How Does This Instrumental Method Differ from Measuring the Speed
of Sound by Time of Flight?
The use of a low frequency Resonant Chamber has significant advantages over
Time of Flight (TOF) methods. It allows the constructive build up of energy within
the Resonant Chamber. Plus, sound transmission in hydrogen at low frequency is
more efficient than at high frequency. This enhances the instrument’s ability to
measure concentration in hydrogen mixtures at lower pressures. Finally, the
careful intelligent manipulation of the applied frequency around the resonant
amplitude peak allows even greater precision in the determination of the speed of
3935
3925
3915
3905
3895
100 200 300 400 500 600 700
Flow (SCCM)
Frequency (Hz)
H2- 300 Torr
H2- 600 Torr
H2- 150 Torr