horiba APMA-370, Operation Manual

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10 APPENDIX
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10 APPENDIX
10.1 Measurement Principle
As shown in the diagram below, the APMA-370 uses the modulation effect that occurs with
infrared absorption of sample gas itself when sample gas and zero gas are alternately sent to
its cell at a certain flow rate using a solenoid valve which is actuated at a frequency of 1 Hz.
Unless the gas concentration of the measured component is changed in the cell, the output
from the detector essentially becomes zero, therefore, the zero drift dose not occur. Since the
APMA-370 also uses the AS-type detector, extremely high-accuracy results are obtained
without no effect of the interference component.
Fig. 101 NDIR measurement principle