how is cpu temp measured

[skimzzz]

I have a slot A AMD motherboard (running a 650 mHZ but afraid to overclock because of overheating) whose bios has temp readings for the CPU and case air temp. I have been trying to maximize heating (new heat sinks, arctic silver 2, etc) and have really checked the temp for the first time. But I noticed that sometimes, the CPU temp is LOWER than the case air temp by 2 degrees C. I know this is impossible and 2 degrees C is quite a spread.

How do mobos measure CPU temp? I have a feeling I have been spending money and trying to max cooling based on bogus CPU readings.

 

[Saturn]

Depending on what kind of motherboard you use, the quality of measurement is different. Some motherboards are very accurate at measuring temperature, and others are not. Also, you should set your motherboard to update and check temperatures often. If you are overclocking a lot, you should have an external thermometer that will read your temperatures. There are many kinds of CPU specific thermal monitors that you can purchase.

<font color=blue> Blowing things up smells Aweful... </font color=blue>

 

[labdog]

can you tell me if my Asus A7v133 is accurate ?

what is thermal monitor price for an Athlon 1.533 FSB266 ?

thanks



EasyInfo
I would like to Invest for my PC !!
ok, buy nothing.

 

[HonestJhon]

The motherboard measure the temp using thermistors...
depending on the ammount of heat, the resistance increases...
there is a thing in the bios that measures the resistance, and since the resistance is a determined thing, then you can pretty much think that it is pretty accurate....for the bottom surface of the cpu....
but you have a slot processor...which has the thermistor mounted pretty close to the core, if it has it...
i dont know how slot athlons are measured, but there has to be some sort of thermistor in the processor itself...but i dont know enough about the slot athlons...
oh, and as far as your cpu being lower temp than your case, that is POSSIBLE, if you have a REAL good heatsink, and REALLY good fan, AND as2, and if the thermistor for the case temp is near a hard drive, or some other heat source...

-DAvid

-Live, Learn, then build your own computer!-

 

[labdog]

"the resistance is a DETERMINED thing."

depend of the resistance error percentage
(electronics components have also error percentage THEMSELF)

more is the resistance quality, less its error percentage is


EasyInfo
I would like to Invest for my PC !!
ok, buy nothing.
<P ID="edit"><FONT SIZE=-1><EM>Edited by labdog on 12/23/01 07:53 AM.</EM></FONT></P>

 

[labdog]

you have 2 separate mechanisms
one measure mb temp, the other cpu temp

because you have a pretty good cooling system, you have succeed to decrease your cpu temp under your mb temp

but it's not unusual

with eg a good water cooling or a cryogenic cooling you can decrease your cpu temp to 27°C or even under


EasyInfo
I would like to Invest for my PC !!
ok, buy nothing.

 

[skimzzz]

It's impossible for the actual CPU temp to be lower than the ambient case air temp, since the CPU is main heat source and is cooled by the case air.

This mobo has a thermometer strip right under the slot a heat sink, so what it actually records is the temp of the HS.

 

[labdog]

but it was


EasyInfo
I would like to Invest for my PC !!
ok, buy nothing.

 

[HonestJhon]

is it touching the heatsink (the strip)
because maybe there is a side that is supposed to be touching the heatsink, and one side that is supposed to be touching the cpu surface. it IS possible for the heatsink to be cooler than the air temp...

-DAvid

-Live, Learn, then build your own computer!-

 

[skimzzz]

There is a strip which just touches the bottom of the slot a HS. I didn't know it was supposed to touch the CPU also. Though this may be difficult since I already put arctic silver on the HS/CPU and dont want to reapply it.

Absent outside interference, how could the HS being at a lower temp than the ambient case air? At best, it would be the same temp and that is only when the computer is off.

 

[HonestJhon]

have you ever felt a heatsink? they are usually pretty cool to the touch, and sometimes really cool to the touch, even if the room it is in is pretty warm...
not sure if the heatsink is actually cooler than the air surrounding it, and logically it couldnt be, but they do sure wick away that heat pretty damn good!

-DAvid

-Live, Learn, then build your own computer!-

 

[skimzzz]

They are cool to the touch because they are conductors and they wisk away heat from your finger (thus the cool feel). This is in contrast to air (which is an insulator). But the actual temperature of the HS is the same as the ambient air temp when both have been in a system for enough time.

Again, absent outside cooling, it is impossible for the HS temp to be lower than the ambient air temp.

 

[HonestJhon]

well, then i dont know how your cpu was a lower temp than the ambient temp...unless your cpu was not putting out much heat...but then again, when you monitor the temp, the computer is on, and the heatsinks fan is on. actively removing te heat from the sink. possibly cooling it below amient. and seeing as how a slot a heatsink is pretty big, there might have not much heat getting to the part with the sensor strip, and since the strip is at the bottom of the sink, and heat travels UP, maybe there was not much heat at the bottom...
but i dont know.

-DAvid

-Live, Learn, then build your own computer!-

 

[labdog]

i think it's a thermodynamic pb associated with air flow.

but for details, i lost the theory class.


if you know you don't know, the way could be more easy.

 

[labdog]

i think it's a thermodynamic pb associated with air flow.

but for details, i lost the theory class


if you know you don't know, the way could be more easy.

 

[knowan]

It's impossible for an air cooled HS to be colder than the air. As for the Asus mobo, Asus is well know for having temp readings that are highly inaccurate (by plus or minus 5C). It's much more likely that Asus put the ambient sensor next to the northbridge or some other component that produces heat then it is for the HS to be cooler than ambient. And Skimzz is right about thermal conductivity of metal.

Don't rely on the Asus temp readings, they can be way off. Your temp readings are coming from the Asus mobo, because the AMD line did not have a built-in temp sensor until the XP line was released a couple of months ago.

--------------
Knowan likes you. Knowan is your friend. Knowan thinks you're great.

 

[Guest]

so i shouldnt trust my 663as ultra motherboard temp that is says in the bios?

 

[labdog]

oops, why my HSF is cold when i touch it ?
im placing a thermometer on my metal case box & it is 1°C under the ambient air just one second after.


if you know you don't know, the way could be more easy.

 

[OldBear]

If your HSF is cool to the touch, it means it is doing a great job. If you could touch it closer to
where it touches the CPU it would be a lot warmer.

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