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AC450NX Rack Server System Product Guide
278
Fan Speed Control Voltage
The server fans operate at two speeds: slow and fast. The low voltage setting allows the fans to
run at a slower speed to minimize acoustic noise under normal conditions. When the Front Panel
Controller (FPC) senses a fan failure or the ambient air temperature sensor reads 30 °C or higher, it
sets the fan voltage to high to increase the fan speed. The ambient air temperature must drop to
28 °C or the failing condition must be cleared before the FPC returns the fans to slow speed again.
When the ambient air temperature reads between 28 °C and 30 °C, the fans remain at their current
speed.
Table 23-1. Fan Speed Control
Fan Failure Ambient Air Temperature Fan Speed Voltage
No <28°C Slow Low
Yes <28°C Fast High
No >30°C Fast High
Yes >30°C Fast High
Speaker
Either the FPC or the PHP I/O baseboard can control the speaker on the front panel board.
I
2
C Bus
The private I
2
C bus monitors failures and voltage margining in the server. The 5 V standby
voltage provides power for the bus, and it is available even when server power is off.
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