Medivance Arctic Sun 2000, Service Manual

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11
2.4 Electronic Control System
The electronic control system consists of two independent subsystems, the Control and the Monitor.
The Control Subsystem performs all of the normal machine operations while the Monitor Subsystem
continually monitors important machine operations with independent sensors. If the Control acts
incorrectly with respect to the safety of the patient, the monitor will disable pump power, thus
preventing inappropriate therapy from being delivered. Each subsystem has a microprocessor,
watchdog, keyboard input circuitry, audio alarm, outlet water temperature sensing circuitry, and
patient temperature sensing circuitry.
The Control Subsystem performs the following functions:
ƒ Command (keyboard) interpretation and information display
ƒ Outlet water temperature control
ƒ Water flow control
ƒ Patient temperature measurement (Patient Temperature 1) and control
ƒ Temperature Out signal generation
ƒ Cold water supply temperature control
ƒ Valve control
The Monitor Subsystem performs the following functions:
ƒ Redundant command (keyboard) interpretation
ƒ Outlet water temperature monitoring
ƒ Patient temperature measurement (Patient Temperature 2)
ƒ Pump power control
ƒ Power supply monitoring
ƒ Data logging output to the RS-232 port
The majority of the hardware comprising the electronic control system is located within the card cage.
The card cage consists of six major elements (See Figure 7.4).
ƒ Power Module: The Power Module includes a 24VDC medical universal input switching power
supply (IEC601.1 compliant), a Mains circuit breaker, cooling fan, heater circuit fuse,
equipotential stud, and solid state relay. The Power Module is connected to the Power Card by
two pigtail connectors.
ƒ Backplane: The Backplane is passive, serving only to connect the four circuit cards listed below.
ƒ Power Circuit Card: The Power Card provides low voltage power regulation to the balance of the
electronics as well as Mains line synchronization (with 4000V isolation from Mains), pump power
control, a Mains loss alarm, and a secondary audible alarm. The Mains loss circuit is powered by
low leakage capacitors and needs no battery.
ƒ Processor Circuit Card: The Processor Card houses the Control and Monitor microprocessors
and their associated circuitry, including nonvolatile memory for each.
ƒ Isolation Circuit Card: Five isolated "islands" of circuitry comprise the Isolation Card. One island
is connected to the Backplane and provides an interface to the rest of the card cage. This island