Novametrix Medical Systems OXYPLETH 520A, Руководство по обслуживанию

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2471 & 2775 Main Board
5-Jun-01 Model 520A Service Manual
27
PRELIMINARY
remaining bits (D6-D0) are shifted out on subsequent falling edges of the CLK
input. On the clock pulse following the one that shifts out the least significant bit
(D0), the CLK and DOUT lines are returned to 3-state and the ADC performs a new
conversion based on the input it receives from the IC33 channel selected by the
A0AUX-A2AUX input address lines.
The ADC sample/convert/store-result cycle is based on internal chip timing and not
the CLK input which (along with CS) only controls serial data output. Thus the CS
line is free to return high once the ADC cycle begins.
Sensor Status Parameters
9.3.13
The sensor (and battery) status parameters input to the multiplexor IC33 are
described below. Note that channel number refers not to the IC33 pin number, but
to the signal label (e.g., channel I0 signal resides at IC33 pin 13).
Channel I0: ADCV12.
This is an extra input to the multiplexer IC33 pin 13. It is unused as of this writing.
Channel I1: Auxiliary Input.
This is an extra input to the multiplexer IC33 pin 14. It is unused as of this writing.
Channel I2: Photodiode DC Level.
Resistors R40, RP8 (pins 1, 2) and capacitor C97 form a voltage divider and low
pass filter that provide a measure of the mean DC level at the output of the
photodiode current-to-voltage amplifier IC40 pin 1. This channel (IC33 pin 15) is
used in determining ambient light interference. If this line is examined while the
sensor’s Red and Infrared LEDs are turned off, then any DC level at IC40 pin 1
must be the result of ambient light impinging on the photodiode. If the DC shift is
in excess of limits set in the software, a Light Interference message appears on the
monitor’s display.
Channel I3: Sensor LED Supply Voltage.
This channel, at IC33 pin 12, monitors the sensor LED supply voltage through a
voltage divider consisting of RP10 (pins 5, 6) and RP8 (pins 1, 8). If a fault occurs
that causes the LED supply fuse F2 to blow, or if the sensor wires are shorted, this
channel reports the condition and the Message Center displays
PROBE FAILURE
.
Channel I4: Incompatible Probe Detection
The input at IC33 pin 1 provides the processor with an incompatible probe indicator
(words probe and sensor are interchangeable). The photodiode output voltage at
IC40 pin 1 will be positive if a SuperBright™ sensor is connected to the monitor.
This positive signal passes through the high pass filter of C73 and RP10 (pins 7, 8)
to the amplifier inverting input IC36 pin 6, where it is summed with the -5 volt
output from IC43. The resultant voltage at IC33 pin 1 will be approxi2.81
volts with no photodiode input. This voltage drops as the (positive) photodiode
signal at IC40 pin 1 increases. If the IC40 pin 1 signal goes negative, as would
happen if a non-SuperBright™ 8600 series sensor were connected to the monitor,