Browse Prior Art Database

Threshhold Speed Circuit for Fan Control

IP.com Disclosure Number: IPCOM000123872D
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2005-Apr-05
Document File: 1 page(s) / 38K

Publishing Venue

IBM

Related People

Mueller, MW: AUTHOR [+3]

Abstract

In some computer systems, the conflict between simplicity and added function always creates the need for design tradeoffs. In computer systems, sensing fan speed usually requires a microcontroller (requiring firmware development) for the function. This disclosure shows how to use part of a PGA (Programmable Gate Array) to accomplish this function. In addition to reporting the speed of the cooling fans, this circuit will also interrupt the service processor if the fan stops turning or slows down significantly, leading to predictive failure analysis.

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Threshhold Speed Circuit for Fan Control

   In some computer systems, the conflict between simplicity
and added function always creates the need for design tradeoffs.  In
computer systems, sensing fan speed usually requires a
microcontroller (requiring firmware development) for the function.
This disclosure shows how to use part of a PGA (Programmable Gate
Array) to accomplish this function.  In addition to reporting the
speed of the cooling fans, this circuit will also interrupt the
service processor if the fan stops turning or slows down
significantly, leading to predictive failure analysis.

   The fans used provide a feedback pulse proportional to the
rate at which the fan is spinning.  This pulse will be used to
increment a counter in our PGA.  This counter will be cleared
periodically by a programmable timer, e.g. once every 100
milliseconds.  The counter will then count the number of turns for
this time interval and be reset.  The output of this counter will be
compared to a value from a threshold register.  The comparator output
will be sampled immediately prior to the resetting of the counter.
If the counter fails to count up and past the threshold value, an
interrupt to the service processor will be driven.  Since the fan
speed is controlled by other resources and can vary, the threshold
register and the timer are programmable (see Figure).

   To sense the speed of the fan, the counter can shift it's
value to a readable register upon clearing, giving t...