5: Central Unit Safety Switch-Off; 6: Central Unit Safety Shut-Down - Honeywell H-S81-HS Operation Manual

General Description
1.5.5 Central Unit Safety Switch-off
During operation, central units cyclically test the main 25V and local 3.3V power supply voltage
values. If one of these values is not within the allowed range, a safety switch-off sequence is carried
out in order to put the whole system in safety condition. During this sequence, the following opera-
tions are carried out:
 Activation of the main FAULT and SYSTEM FAULT outputs.

Deactivation of the main RUN output.

Deactivation of the RUN LED on the CPU

PANEL SHUT-OFF indication on the display
In this condition, output status is frozen. Restart the system to clear this condition.
• Allowed 25V voltage range: 18.5 - 32VDC (A warning condition is reported with voltage
values <22.5 V and >29.5.)
• Allowed 3.3V local voltage range: 3.15 - 3.6VDC (This function is carried out by an external
reset circuit with voltage values >3.15 V.)
In the configurations with redundant CPU, if the sequence is carried out only by the primary CPU,
the secondary one signals primary CPU failure and starts controlling the system without any inter-
ruption of system operation. If, instead, the sequence is carried out only by the secondary CPU, the
primary one signals secondary CPU failure and keeps carrying out its functions.
1.5.6 Central Unit Safety Shut-down
In case of critical failures during operation, the central unit will carry out a safety shut-down
sequence in order to put the whole system in safety condition. The following failures will cause a
safety shut-down:
• Error in checking memory content (Flash/Ram).
• Internal hardware failure
Restart the system to clear this condition.
In the configurations with a redundant CPU, if the sequence is carried out only by the primary
CPU, the secondary one signals primary CPU failure and starts controlling the system without any
interruption of system operation. If, instead, the sequence is carried out only by the secondary CPU,
the primary one signals secondary CPU failure and keeps carrying out its functions.
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Figure 1.7 Digital Output Test
H-S81-HS Installation & Operation Manual — P/N LS10114-000HI-E:A 2/24/2015
Safety-Related Modules in the H-S81-HS System