Introduction 9 Anesthetic Gas Module
171
General Measurement Principles
The Philips M1026A Anesthetic Gas Module uses a technique called Non-Dispersive Infrared Gas
Concentration Measurement (NDIR) to measure the concentration of gases.
This works as follows:
• The gases that the Philips M1026A Anesthetic Gas Module can measure absorb infrared (IR) light.
• Each gas has its own absorption characteristic. The gas mixture is transported into a sample cell, and
an IR filter selects a specific band of IR light to pass through the gas. For multiple gas
measurements, multiple IR filters are used.
• The higher the concentration of gas in the mixture the more IR light it absorbs. This means that
higher concentrations of IR absorbing gas results in lower transmission of IR light.
• The amount of IR light transmitted through an IR absorbing gas is measured.
• From the amount of IR light transmitted, the concentration of gas can be calculated. This
calculation provides the gas concentration value.
O
2
gas cannot be measured with this technique as it does not absorb IR light. Hence O
2
gas is
measured with a sensor that makes use of the paramagnetic properties of O
2
for its fast measurement
technique.
Theory of Operation
Figure 30 shows the functional blocks within the Philips M1026A Anesthetic Gas Module.
Figure 30 Anesthetic Gas Module Functional Block Diagram
The main components of the Philips M1026A Anesthetic Gas Module are:
• Main PC Board.
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