Introduction 9 Anesthetic Gas Module
177
Figure 33 Anesthetic Gas Module Measurement Assembly
The measurement assembly contains the following subassemblies:
IR Source: The ceramic IR source is heated to 600°C by applying a
constant drive voltage across it.
Filter Wheel Assembly: The filter wheel assembly includes IR filters for the anesthetic agent,
CO
2
, N
2
O and a reference channel. A blank segment (dark period)
marks the beginning and end of the filter series.
Sample Cell: The sample cell is a stainless steel tube. It has non-IR absorbing
sapphire windows at both ends, and barbed inlet and outlet ports.
The inlet and outlet ports are placed as close as possible to the
windows so that the gas flows effectively through the cell.
Preamp Assembly The preamplifier board assembly includes an IR detector, an IR-
detector thermistor, a TE cooler, and a pre-amplification circuit. The
output from the preamplifier is a stream of pulses; this pulse train has
one pulse for each IR filter, and is terminated by a blank period (dark
level phase) (see Figure 34).
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