Fresenius Medical Care 4008 E Technical Manual page 356

2nd phase:
The watchdog is triggered too slowly; switch-off of the 24-V voltage is monitored. As soon as the
voltage has fallen below a specific value (<5 V), the watchdog is again triggered by CPU 1 in the
correct time-reference and a trigger request is transmitted to CPU 2.
After having recognized the trigger request, CPU 2 checks the permissible voltage level and, with
all prerequisites being fulfilled, emits a release pulse for the output-stage flip-flop (WD_RESET).
With the function being correct, the 24-V voltage is again switched on. The increase of the 24-V
voltage is monitored.
The 2nd phase is now completed successfully.
3rd phase:
The watchdog is triggered too rapidly; switch-off of the 24-V voltage is monitored. As soon as the
voltage has fallen below a specific value (<5 V), the watchdog is again triggered by CPU 1 in the
correct time-reference and a trigger request is transmitted to CPU 2.
After having recognized the trigger request, CPU 2 checks the permissible voltage level and, with
all prerequisites being fulfilled, emits a release pulse for the output-stage flip-flop (WD_RESET).
With the function being correct, the 24-voltage is again switched on. The increase of the 24-V
voltage is monitored.
The 3rd phase is now completed successfully.
4th phase:
The watchdog is triggered by CPU 1 in the correct time-reference. The 24-V voltage must be
applied.
CPU 2 emits an inhibit pulse (WD_SET) to the reset input of MF2. The output of MF2 acts on the
output stage and resets the output-stage flip-flop, thus inhibiting the energization of the relay. The
24-V voltage is switched off, this being monitored by CPU 2.
As soon as the voltage has fallen below a specific value (<5 V), the cut-off route of CPU 2 is
tested, and CPU 2 emits a release pulse for the output-stage flip-flop (WD_RESET).
With the function being correct, the 24-V voltage is again switched on. Achieving of the 24-V
voltage level is being monitored.
The 4th phase is now completed successfully.
Only after the above sequence has been completed correctly will the 24-V voltage for the further
function run be switched on.
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Fresenius Medical Care 4008 4/09.03 (TM)