GE HEALTHCARE E-PSMP, Technical Manual

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Module Frames and Modules
10 - 8
2062973-004
1.3.3 MiniC sensor
The miniC sensor is a non-dispersive infrared analyzer measuring absorption of the gas sample
at 4.2 to 4.3
μ m infrared wavelength, which is selected using an optical narrow band filter. The
IR lamp is a filament surrounded by thermal isolation. There is a hole in the isolation, passing
the radiation to a conical measuring chamber with 3 mm length. From the sample chamber,
the radiation goes into a thermopile detector with an optical filter in front of it.
The temperature sensor measures the miniC sensor's temperature and it is used for
temperature compensation.
The miniC sensor is connected to the CPU board and they can't be replaced separately.
Figure 6 MiniC sensor
1.3.4 CPU board
The CPU board contains a processor, memories and all the analog signal processing needed. A
miniC sensor is attached to the board with a flexible PCB. Also supply voltage and an RS485
serial channel are connected to the CPU board using another flex cable.
Analog signals (CO
2
, temperature, absolute and differential pressures, and lamp current
signals) are fed to the 16-bit A/D converter. The processor controls the A/D converter and
calculates the CO
2
percentage and respiration rate from this data.
The processor controls sample flow by adjusting the pump voltage based on the differential
pressure signal. The processor also controls the current of the IR source and keeps it constant.
Calibration data is stored on the EEPROM.