Detailed Description Of Block Diagram - Dräger 8000 IC Function Description

2.2.2

Detailed description of block diagram

The numbers in brackets refer to the position in the block diagram.
2.2.2.1 Air temperature sensor (39)
The air temperature sensor is part of the feedback loop of an operational amplifier (31B). This
operational amplifier produces an output voltage proportional to the air temperature. A second
amplifier stage modifies the voltage to the input voltage range of the ADC. Resolution: 0.0 °C
to 60.0 °C = 0.0 to 5.0 V.
2.2.2.2 Over-temperature sensor (38)
The over-temperature sensor is mechanically integrated with the air temperature sensor in one
housing. This allows a redundant measurement for the air temperature. The amplification
factor and thus the output signal differs from the output signal of the air temperature sensor.
The air and over-temperature sensor are checked crosswise by software. In case of a
temperature difference of more than 0.5 °C a sensor alarm is produced. The over-temperature
sensor is placed in the feedback loop of the operational amplifier (31A). A second amplifier
stage modifies the voltage to the input voltage range of the ADC. Resolution: 0.0 to 50.0 °C =
0.0 to 5.0 V.
2.2.2.3 Over-temperature comparator (29)
The output voltage of the over-temperature sensor circuit is additionally monitored by a
comparator. The trigger level of this comparator is set to 40.0 °C. If the over-temperature
sensor output voltage reaches this limit independent and unaffected by the microprocessor
this comparator switches off the heater and sets the incubator into the safe operation mode.
The over-temperature condition is stored and latched by a bipolar relay (16). After the
temperature has fallen and the over-temperature sensor circuit is reset by the operator with a
dedicated reset button, normal operation of the temperature control system is continued.
2.2.2.4 Testing of over-temperature comparator (36)
Every 10 minutes the over-temperature sensor circuit (comparator) is tested by the
microprocessor. On the Analog PCB the relay (K2) or by FET transistors on newer devices as
of 1996 substitutes for a short time the over-temperature sensor with a fixed resistor simulating
a temperature higher than 40.0 °C.
6141.22X Incubator 8000 IC/SC/NC
Function Description
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