Dräger Medical Babytherm 8004, Technical Documentation Manual

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Function Description Babytherm 8004/8010
Receiver and transmitter for serial data transfer
Optocouplers transmit the serial measured data (mattress heater, skin tem-
perature) to the WT Power PCB. An optocoupler receives the serial test sig-
nals for the measuring circuits. An optocoupler transmits the overtemperature
signal to the Power PCB.
Selection logics of test signals
An addressing module and a shift register convert the serial test signals into
parallel data.
The test signals activate the following test circuits:
– Overtemperature of mattress heater (41.6 °C)
– Skin temperaure (36 °C)
Measuring amplifier (skin temperature, mattress heater)
Two skin-temperature hybrides measure the skin temperature.
Four measuring amplifiers (NTCs) measure the mattress temperature in
pairs. The NTCs are fitted in pairs to the mattress heater. The measured val-
ues of one measuring pair must not deviate by more than 0.5 °C from each
other. Both measuring pairs must not deviate by more than 5 °C from each
other. One measuring amplifier for each pair evaluates the overtemperature
of the mattress heater (greater than/equal to 41.6 °C).
Overtemperature comparators
Two comparators evaluate the signals for the mattress heater overtempera-
ture. The comparators are adjusted to a voltage value that corresponds to a
mattress temperature of greater than/equal to 41.6 °C.
If the mattress temperature reaches or exceeds 41.6 °C, the output level of
the respective comparators goes towards zero volt. The safety relay of the
mattress heater is switched of by the hardware.
Test circuit (41.6 °C mattress heater)
A test circuit checks the function of the mattress heater overtemperature
comparator at regular intervals.
Test circuit (36.0 °C skin temperature)
The software checks the skin-temperature hybrides.
The test circuits are provided with reference resistors. They are located at the
inputs of the skin-temperature hybrides. The output voltage values of the
skin-temperature hybrides correspond to a temperature of 36.0 °C.
A/D conversion with multiplexer
The multiplexer transmits the analog measuring signals of the skin tempera-
ture to the integrated A/D converter. The serial output signal of the A/D con-
verter is applied to an optocoupler.