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The instruction to the situation that the fan would run suddenly when the VIS was power-off

Publication Date:  2012-09-29 Views:  170 Downloads:  0

Issue Description

The client found that the fan module run when the API switch was off with the normal input of the AC in VIS several times.

Alarm Information


Handling Process


Root Cause

The fan speed of the VIS is controlled by BMC, as long as the AC input is normal, BMC will run. So the phenomena above must result from the fan timing.
Two reasons for instruction:
1、 Background & related knowledge:
There are two systems running in VIS6000, the big system and the BMC system.
When the AC input to VIS6000 is normal and the API switch is ON, the status of the big system is running while the BMC system runs when the AC input is normal no matter whether the big system runs or not.
During the fan timing, the BMC system has a value of “demand rev” avoiding the big span during the fan timing.
2、 The fan timing strategy when the big system of VIS is power-off
When the API switch is off, the “bang-bang” strategy is used in fan timing, which means the fan rev is not static.
When the API is off, the fan rev is set up with 1, but the actual fan rev can’t be 1 all the time. When the actual rev is less than 1, the “demand rev” will increase and the fan starts to run. When the actual rev is more than 1, the “demand rev” will decrease and the fan will slow down.
When the gap time is small between two actual revs, the fan may speed and slow in a sudden which may make a sound occasionally.
Consulting the research engineer, this design is for heat dissipation.


When the API switch is off, the “bang-bang” strategy is used in fan timing. There may be some sound occasionally generated by the fan rev strategy instead of the hardware failures which is normal.