Cocoon CWS 4000 - Sensor Board; System Block Diagram

Care Essentials CWS4000 Cocoon Warming System Service Manual
Power-On Reset
Following power-on capacitor (C3) charges from zero to +5V (VCC) through resistor (R1)
connected to ground. This causes the Reset input of the microcontroller to be momentarily
asserted high. The microcontroller type used on Control Board revision E and later has an
internal power-on reset circuit and capacitor (C3), resistor (R1) and diode (D1) are not fitted.
Watchdog Reset
The microcontroller watchdog timer is incremented regularly by the microcontroller hardware.
When a watchdog timer overflow occurs the microcontroller is reset.
To prevent such a system reset the microcontroller watchdog timer is reloaded before it
overflows by the application software program. If the microcontroller suffers a hardware or
software malfunction, the application software program will fail to load the microcontroller
watchdog timer. This failure will produce a system reset on overflow thus preventing the
microcontroller from running out of control. This prevents a potentially hazardous situation from
occurring.
6.2. Sensor Board
Digital Temperature Sensor
The temperature sensor (U1) is controlled by and communicates with the Control Board
microcontroller (U1).
Temperature Limit Thermostats
The maximum air temperature is not only limited by the control system but by two series-
connected bimetallic auto-resetting thermostats. These thermostats are located in the exhaust
air stream and will interrupt power to the CWS4000 should the output air temperature exceed a
predetermined limit. The temperature limit thermostat function does not require adjustment,
calibration or performance inspection.
6.3. System Block Diagram
The System Block Diagram shows the general electrical connectivity between the various
CWS4000 electrical and electronic subassemblies:
e Power inlet module including EMI filter and fuses.
e Temperature limit thermostats.
e Heater.
e Fan blower.
e Control Board.
e Sensor Board.
e Communications connector.
Before removing any of the connections between the electrical and electronic subassemblies,
make a careful note so that these may be correctly reinstated. Incorrect connections could
compromise patient safety and/or damage the CWS4000.
The System Block Diagram is presented as an aid to understanding the CWS4000 and does
warrant extensive discussion.
Revision | 13 June 2006 Page 15