6141.22X Incubator 8000 IC/SC/NC
Function Description
09.99 Page 44 of 49
c. over-temperature alarm
The bistable relay for the over-temperature alarm is installed on the Motherboard PCB. The
excitation winding is triggered by the hardware via X2/20c from the PCB Analog and by the
software via port PB6 from PIA D1. By contact K1.l the relay position is read in and evaluated
via port PA0 of PIA D1. Through contact K1.2 a cutoff relay is driven for the actuators.
Excitation of the reset winding is done via port PB4 of PIA D1. C16 prevents continuous driving
of the reset winding due to a defective port PB4 and thus that a a pick up of the relays in the
event of over-temperature is made impossible.
d. fan failure alarm
The fan is monitored by the voltage pulses induced in a coil by two permanent magnets which
are attached at the impeller. The negative pulse triggers the mono flop D6A via the inverting
amplifier N1. Via port PA6 of PIA D1 the signal is evaluated. Via port CB2 of PIA D2 the circuit
function may be tested by pulling down the input of the circuit to a lower voltage level. Thus
the fan pulses become ineffective.
e. watchdogs
Mono flops D3A and D3B form the two watchdogs for driving of the heatings and the valves.
The watchdogs monitor the chronological program flow, separate for background and IRQ-
level. Mono D3A is re-triggered via address 8030h in the background, mono D3B via address
8040h in the IRQ. The maximum re-triggering time is 100 ms. Both output signals are
interconnected logically and with a further interconnection of the trigger signals for the
heatings and valves lead to a release resp. blocking of these actuators. Moreover, in case one
of the mono flops is elapsed the beeper is activated independent of the software.
f. +5 V voltage monitoring
The digital supply voltage of 5 V is monitored by a window comparator for high and low voltage
conditions. The limits are set to 4.4 V and 5.5. V. If the window comparator senses high or low
voltage, the 24 V power supply for the solid state relays and the oxygen valves is interrupted
by the relay (17). Via transistors V15 and V16 the comparator limits to test the function of the
voltage monitoring can be adjusted. This is done by the software via ports CA2 and CB2 of PIA
S1 (10-Minutes-Test).
Normal operation: CA2 = L-level; CB2 = H-level
Test upper limit: CA2 = H-level; CB2 = H-level
Test lower limit: CA2 = L-level; CB2 = L-level
The +5 V supply voltage is also monitored via a watchdog circuit (25A) on the CPU PCB (25).
This watchdog circuit cannot be tested during operation because it triggers a reset.
To Next Page
Loading...
