| title: | About the quot CPU temp quot output of ADM1 |
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Hi Rudolf,
Thank you for your reply.
On 10/23/06, Rudolf Marek <r.marek at assembler.cz wrote:
Hi Yongkui
I calculated the time constant based on the temperature curve of "CPU
temp". It is about 20 seconds.
Ok. Important question: Is the fan switched off - disconnected? I think we
see
the "slow" start because the system cools down. The board has some kind of
automatic cooling. Of course without the fan it might be bit dangerous if
system
temperature grows, but I think this is necessary to test it ;) Or if you
are
curious and want to test it ;)
Yes, the fan is connected and running all the time. I plan to test it
without the fan this weekend. I will let you know the new high temperature
without the fan as soon as possible.
In my opinion, the time constant of the silicon chip is about 10
milliseconds.
Well what constant?
The thickness of the silicon chip is about 0.5mm, the thermal resistance is
about R = 0.4 K/W, the thermal capacitance is about C=0.025 J/K, so the time
constant = R*C = 0.01 second.
The time constant of the heat sink is about several minutes.
So it is my expectation that although the temperature of the silicon chip
changes rapidly, the temperature of the heat sink changes very slowly (in
minutes). So if the thermal diode is not inside the silicon layer but near
the heat sink or heat spreader, then the temperature change will be as slow
as the temperature curve of my experiments (or even slower).
Does this suggest that the "CPU temp" is not the temperature of the
thermal diode inside the Pentium 4 CPU?
Also from the previous mail with graphs, I think it is but system is
cooled
Oh, I just thought of one possible reason for this. Perhaps the current
or the voltage drop of thermal diode is not changing so fast as the
temperature change of the silicon area around it. So the temperature
readings from the diode will lag. If this is true, this could explain
why the readings from the thermal diode is not changing as rapidly as
the temperature of the silicon area around it.
Yes but not in range of hundreds of seconds.
I am confused here. I still think the "CPU temp" should be the readings
from the thermal diode inside the Pentium 4 CPU chip. But the fact that
this "CPU temp" is changing slowly in seconds and it could not reach a
high temperature makes me doubt it.
I think because of that hidden autoregulation. I would suggest to
disconnect the
fan connector (of course not the heatspreader ;) and try it without that.
Will the hidden autoregulation (cpu fan speed change) prevent the
temperature of the silicon chip from increasing rapidly (from tens of
milliseconds to tens of seconds)? I have doubt on that.
Anyway, I plan to try it without fan working to see what will happen.
Sorry for delay,
Regards
Rudolf
Thank you very much for your ideas on this!
Regards,
Yongkui
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