Dräger Medical Babytherm 8004, Technical Documentation Manual

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Babytherm 8004/8010 Function Description
Mattress heater control and scan
The operating voltage of the mattress heater is approx. 24 VAC. The heating
circuit is electrically isolated from the direct voltage and protected with a fuse.
In the event of a malfunction, a safety relay interrupts the heating circuit. Dur-
ing operation, a triac switches the heater. An upstream zero voltage and
phase group switch switches the heater on only during the positive pass of
the AC voltage and off during the negative pass of the AC voltage.
The voltage drop at the mattress heater and a parallel-connected optocoupler
generate pulses which activate a monoflop. The output of the monoflop sig-
nals the operating status of the mattress heater.
Figure 20 Block diagram 3 of WT Power PCB