Theory
91518 Multigas Analyzer Service Manual 3-4
Memory Circuits (RAM and Flash ROM)
The memory circuits provide program memory for the MCU. The RAM is used for loading the software program
and data. The flash ROM is used for storing the software program.
SDLC Interface
The 91518 Multigas Analyzer communicates with the Spacelabs Healthcare monitor using a SDLC interface
that is common between all current Spacelabs Healthcare monitors and modules. The Multigas Analyzer can
use both 9-pin and 26-pin SDLC cables, depending on the Spacelabs monitor that is used. Refer to Multigas
Setup on page 2-2.
Test Indicator LEDs Circuit (Factory-Use Only)
The LED indicators are used for testing. Refer to Troubleshooting on page 5-1.
Gas Analyzer Unit
The OEM gas analyzer unit (P/N 010-1651-00) is a discrete device that measures the concentrations of gases.
Anesthetic agents or mixtures of two anesthetic agents are automatically identified and concentrations of the
identified agents are measured. The analyzer also detects mixtures of more than two agents and issues a
AGENT MIX message.
The gas analyzer unit consists of:
• Gas sampling system
• Gas measuring unit
• OM measuring unit
• CPU board
• OM board
Gas Sampling System
The sampling system takes care of drawing a gas sample into the analyzers at a fixed rate. The gas sampling
system samples the measured air to the analyzer and removes water and impurities from it. A sampling line is
connected to the water trap. The pump draws gas through the sampling line into the gas measuring unit. After
the gas measurements, the gas is exhausted through the sample gas out connector.
A larger pressure difference makes the deformations of the gas concentration curves less sensitive to high
variations of the airway pressures.
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