6141.22X Incubator 8000 IC/SC/NC
Function Description
09.99 Page 25 of 49
2.2.2.23 Thermal switches heaters
The air heater is protected by a thermal circuit breaker (9) that interrupts the power for the
heater in case of over-temperatures. The humidifier is equipped with two thermal switches.
One is used to interrupt the power (10) in case of severe overheating. The second thermal
switch (7) operating at a lower temperature level is used to indicate the microprocessor that
the water supply is empty which causes a rise in the temperature of the humidifier.
2.2.2.24 Display driver and keyboard interface (26)
The 7 segment display and the LED's are driven by special integrated circuits which are used
in every module. The keyboard interface of the Air Temperature Display PCB is part of one of
these circuits and reads all keys (button switches) from all modules.
2.2.2.25 Mono stable flip-flop for INOP LED (24)
The Inop LED is driven by a mono stable flip-flop with a time constant of 100 ms. This mono
stable flip-flop is addressed by the unique address during the background routine.
2.2.2.26 Power supply and battery (15)
The power supply delivers voltages of +5 V, +15 V, -15 V and +24 V. A NiCad battery
integrated into the power supply serves as the power source in case of power failure to drive
the signal transducer and the power failure LED.
2.2.2.27 Power fail detection (23)
If half waves of the AC power supply voltage are missing because of disturbances or
interruptions or because the Incubator has been switched off at the main power switch, a NMI
(Non Maskable Interrupt) is activated. The software will immediately check the position of the
main power switch and based on its position initiate a "cold" or "warm" start.
2.2.2.28 Driver for the beeper (22)
The beeper is driven by a digital signal of PIA1. Very short pulses to the beeper are
suppressed by a filter to avoid spurious noise during testing. In case of a power failure the
beeper is activated independently of the microprocessor and powered by the battery.
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