Smiths Medical BCI 3304, Руководство по обслуживанию

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Chapter 2: Oximeter Circuit Description
3304 Service Manual 2-1
Functional Structure
The functional structure of the oximeter is shown in drawing no.
71200S1. The oximeter consists of the main board, the display board,
two key labels, speaker, probe connector assembly and the battery:
The oximeter board contains the battery charger, power •
supplies, the on/off control logic, speaker control circuitry,
the microprocessor, and the data acquisition circuitry. It also
includes isolated RS-232 printer interface.
The display board contains the 7-segment displays, the led bar •
graph, the indicator lights, LED driver chips. The display board
connects to the main board through an fourteen-conductor
ribbon cable.
The key labels contains the front panel touch keys. •
The probe connector assembly is a cable connecting main board •
with patient probe.
Battery Charger
general Description
The wall mount charger has an unregulated 12 V DC output that
comes into the main board at J10. Transorb D13 prevents electrostatic
discharges from entering the system. The charger circuit built around
linear regulator U27 generates a constant charging current of 0.138A
defined by resistors R66, R67 and R68. The comparator U28A and U28B
monitors the voltage on the battery, and at 7.2V turns off U27. The
trickle charge current is then defined by resistor R70. Capacitor C92,
being in the discharged state at power up, provides the initial high
current condition of the charger. If the battery is fully charged, the
ciruitry switches to the trickle current mode in a few seconds.
Chapter 2: Oximeter Circuit Description