Datex-Ohmeda S/5 B-GAS, Technical Reference Manual

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Datex-Ohmeda S/5 Anesthesia Monitor
Document No. 800 1005-1
16
2.2.2 ACX-200 measuring unit
The ACX photometer is of dual path type. The infrared light beam passes through a measuring
chamber containing the gas to be analyzed, and a reference chamber, which is free of CO
2
, N
2
O,
and AA. The measurement is made by determining the ratio between the two light intensities.
Figure 9 ACX photometer (ACX-200 measuring unit)
A filter wheel is used to control the light from an incandescent lamp that passes through the
photometer. The filters are arranged so that the light is passed sequentially:
•
first at the CO
2
absorption wavelength through the reference chamber
•
then through the measuring chamber
•
finally it is blocked completely
The same sequence is repeated at the N
2
O and anaesthetic agent gas absorption wavelengths.
After passing through the filters the light is reflected and focused by a mirror onto the infrared
detector. This detector measures the three light levels for each gas described above.
There is an optical sensor incorporated in the photometer which detects light from a reflective
surface on the filter wheel once every revolution. The pulses from this sensor are used to
synchronize the electronics to the signal from the infrared detector. A stabilizing diode measures
the temperature, which is needed to compensate for thermal drifts. The infrared detector, the
optical sensor and the stabilizing diode are mounted on the preamplifier board.