CPU Temp Question...

[WyrmMaster]

OK heres the situation:

A newbe comes into the forum and askes the o so common question "my CPU is running at BLA, is this ok."

Someone usually comes in and says, thats a little hot, you shoud try to keep the temp under 50c. OK, so the newbe, who happens to be running an Epox 8K7A, gets a new case fan, and his temp dropes to 39c, measured by the onboard thermister ofcoures.

Right now, running folding, MBM shows a CPU temp of 39c on my board, like i used in the example. However, my Compunurse Reads 55c. My point is, what reading does the general keep it under 50c statement come from. A real temp probe, or MBM.


I did not intend to offend any newbies with this post, im just trying to make a point.

[Hoot]

If you have the compunurse sensor mounted properly, then I'd say believe the compunurse. Here's what I mean by properly:

Many in-socket thermistors (use by MBM) touch the CPU bottom off center, if not at all and hence don't read anywhere near the actual core temperature. Many of those insocket thermistors are suspended upwards on their leads. You can often bend them to not only touch the bottom of the CPU, but also right under the core. Applying a small dab of thermal compound on them will enhance their accuracy. Done right, You can get temperatures within 2C of the top of the core, though the temperature reading will respond a little slower due to the heat needing to propagate through the ceramic. The next reply contains a crude diagram showing what I mean by bending the thermistor.

Hoot

[Hoot]

Bending in-socket thermistor example (crude).

Hoot

[WyrmMaster]

I believe teh Compunurse, im just wondering if the keep it under 50c advice reffers to MBM or actual temps, and also the valididy of that advice.

[Hoot]

It means using the most accurate measurement method that you can reasonably implement. There is the obvious danger of frying a CPU if it reaches a certain temperature. That, we can all agree upon. What a lot of people do not realize, is that the temperature of the CPU impacts how high you can overclock it. Holding my 1.0G Tbird to less than 40C, (under load, not idle) I can run it up to 1550 Mhz. My speeds fall off as follows:
40C 1500 Mhz
42C 1450 Mhz
45C 1400 Mhz
50C 1333 Mhz
>50C I never let it get that high.

That is the characteristics of my particular Tbird. Your results will vary a little one way or the other, but not by much. I have both type T and K digital thermometers in my shack. I calibrated my compunurse using a type T thermocouple inserted in a small hole I drilled in the middle of my HSF that allows the thermocouple to sit directly on top of and in the center of the cpu core. The hardest part is isolating the thermocouple as much as possible from contacting the HSF where it passes through, because if it does, the HSF will wick away some of the heat it sees through conduction. It's a tricky process. I have 6 HSFs for tinkering and everyone has a hole in it. I use the compunurse under normal conditions because I don't want my Fluke Digital thermometers stuck sitting on top of my case.

Hoot

[WyrmMaster]

That sounds about right, with mine running in the mid 50's i cant get over 1350, and thats not stable. its fine at 1328 though.

Im kinda wondering whats wrong with my heatsink. SVC Golden Gate with Delta. C/W is supposed to be around .22, but based on my temps its more like .36. Maye i need to get a Glaciator.

[Hoot]

Just a note that the Quality Control on the compunurse and other similar units is not very good. I went through three of them before I found one that naturally read correct. One fellow who was also implementing one found it off by 10C from a known good indicator. If you don't have a known good calibration device, tuck it under your armpit tightly, right up against the skin for 5 minutes. It should read between 36 and 37C. You can bias the thermistor a little bit to adjust the accuracy, but its tricky removing the series SMD resistor inside the readout and replacing it with a 10-turn trim pot. It is more work than its worth.

Hoot

[WyrmMaster]

I tried the low end, by holding it against an ice cube, and it got down to 1c, so its pretty good there. I still have to test the high end though.

Edit: I just tested my armpit, it got up to 36c.

[WyrmMaster]

Well, i emailed svcompucycle, hopefully they will replace the heatsink, C/W of .37 is just not right. I tried re applying past, no luck. The only thing i can think is that the heatsink is defective.