Datex-Ohmeda CAPNOMAC ULTIMA, Service Manual

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CAPNOMAC ULTIMA
TM
SERVICE MANUAL
5-20
5.5
SpO
2
measuring board (Rev. 06 and up)
Block diagram and schematic diagram part 1
Figure 5.10
Parts layout, timing diagram, and schematic diagram part 2
Figure 5.11
Signal waveforms and schematic diagram part 3
Figure 5.12
Schematic diagram part 4 Figure 5.13
The board is intended to perform the following tasks:
Control the LED light sources of the probe.
Amplify the signal coming from the detector and separate
the red and infrared signal components to respective
channels.
Multiplex in both channels the alternating component of the
signal (plethysmographic pulse) with the signal proportional
to the total intensity measured with the respective
wavelength.
Provide isolated output from the multiplexer channels (red
channel and IR channel) to the SpO
2
Processor board.
Power supply
The isolated power supply consists of:
- 32.768 Hz oscillator.
- Half-bridge converter with isolation transformer.
- Stabilization and filtering of the output voltages with linear
regulators.
- Protection of the overloading with PTC-type thermistor.
Timing/LED control
The timing pulses are produced by a PAL (Programmable Array
Logic) D3. The input signal for D3 (SYNC.) is taken from the
switching power supply as a 32.768 Hz square wave. All timing
signals are synchronized at this switching frequency. The timing
circuit controls the LED driver circuitry (signals LED
R
and
LED
IR
), the RC time constants in amplifier chain (MEASURE)
and sampling (SAMPLE
R
, SAMPLE
IR
).
LEDs in the probe are driven with constant current pulses, (90 or
300 mA). The pulse duration and duty cycle can be seen in timing
January 15th, 1997/6