Nellcor N-180, Руководство пользователя

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N-180 Pulse Oximeter Service Manual
3-12
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Control signals:
Refer to figure FO10-1 (sheet 4 of 7 and sheet 7 of 7). Measuring SpO
2
is
controlled by logic signals from micro controller U5. The control signals
are listed and defined below:
IRGATE* is a result of micro controller output PWM1* ANDed with output
CMT1. IRGATE * controls the transmission of the IR on and off levels
into the IR Filter and amplifier.
IRLED* from micro controller output CMSR4. IR
LED
* controls the selection of
the LED drive level at U4B and the direction of current applied to the
sensor LEDs.
REDGATE* is a result of micro controller output PWM1* ANDed with output
CMT0. REDGATE * controls the transmission of the red on and off
levels into the red filter and amplifier.
REDLED* from micro controller output CMSR5. REDLED* CONTROLS the
selection of the LED drive level at U4A and the current direction
applied to the sensor LED s.
SATIN from micro controller output CMSR3. SATIN controls the inverting
amplifier through U10B and U14A.
Analog to Digital Conversion
Analog to digital conversion (figure 3-5) is accomplished by a dual-channel
device (U20) that produces a multiplexed serial output. Channel 1 (AIN1)
accommodates either VCAL1 voltage or the analog pulse waveform from the
red filter and amplifier channel. Channel 2 (AIN2) accommodates either
VCAL2 voltage or the analog pulse waveform from the IR Filter and amplifier
channel. These selections are determined by the configuration of quad field
effect transistor (FET) switch U24A, B, C, and D. Switching is controlled by
logic signal RESISTORS.
Logic signal ADCCHN determines the output bit stream multiplexing from
device U20. In turn, bit stream multiplexing determines the channel present
on the ADCDATA line. The ADCDATA line is coupled directly to micro
controller U5 for conditioning prior to transmission to the monitor display
processing circuits.