| Forum Home | ||||
| Press F1 | ||||
| Thread ID: 52362 | 2004-12-17 04:49:00 | CPU temperature results | Terry Porritt (14) | Press F1 |
| Post ID | Timestamp | Content | User | ||
| 304495 | 2004-12-22 04:36:00 | It's all fairly basic, but the relationship between temperature rise, flatness, surface finish and thermal compound thickness should be explained more fully by the manufacturers of heatsinks and thermal compounds. Here is an overclockers site that looks at thermal greases and does the same calc. as I've done more or less: www.overclockers.com But notice that he derives correctly an expression for thermal resisitance and the units are deg C/Watt if you check the formula. Then he quotes the manufacturers crazy mixed units for thermal resistance as deg C. inch squared per watt for a 0.001 inch layer. That is just plain confusing. Looking through my school exercise notebook for 1st year sixth form, I think that is year 12? There is a nice experiment for measuring thermal conductivity using the LEES' disc apparatus, I wonder if our Graham knows about that :) The main purpose for fitting a thermocouple against the cpu face is to calibrate the internal cpu thermal diode. I cant think of any other way of finding out how accurately that temperature is reported by the BIOS. |
Terry Porritt (14) | ||
| 304496 | 2004-12-22 07:00:00 | According to AMD they don't recommend grease on "lidless" ie no heat spreader CPU because it tends to dry out after a time leaving voids especially if it was thinly applied. Phase change pads are reasonably foolproof and a few degrees don't matter so long as the case get decent airflow.The grease they do approve does change with heat and becomes denser. As far as thermal probes go, even CPU with on-chip diodes have the problem that the diodes aren't in the hottest part of the core so some correction has to be done to compensate. |
PaulD (232) | ||
| 304497 | 2004-12-22 08:05:00 | Following on from what Pauls says, here is what AMD says on the the topic: here (www.amd.com) I think drying out is somewhat of a red herring, especially when you think of power transistors, where conventional white thermal paste is most often used. Maybe after about 5 years? one should think about renewing the paste. The other thing is that I notice is that AMD thermal pads cost $10.80 each from Ascent. So if you remove a stock AMD HS&F it's going to start getting expensive to replace the phase change pad. I have been using Titan TTG S101 silver grease on an AMD 1.33 Thunderbird for a full 2 years now, with no observable temperature rise due to any drying out or leaking out, so I'm reasonably happy about that aspect. |
Terry Porritt (14) | ||
| 304498 | 2004-12-22 09:35:00 | Without wanting to state the obvious, but doesn't the real value of thermal grease come in once you start overclocking? I mean, the fact of the matter is that you are measuring temperatures of CPU's which aren't even under load or overclocked. Once you start overclocking and measuring temperatures, along with ambient temperatures, etc then you get some real value. The way i read it, you are forgetting about the benefits of stock cooling vs aftermarket cooling in overclocking or high stress applications. Lo. |
Lohsing (219) | ||
| 304499 | 2004-12-22 11:55:00 | what I'm starting to wonder is what your trying to achieve,The conclusion that your heading to is that stock cooling is fine on a cpu running at stock speeds,and that thermal paste does its job as designed. Not exactly new knowledge, Or anything that had to be proven. |
Metla (12) | ||
| 304500 | 2004-12-22 12:29:00 | It's very interesting all the same . There is also a lesson that we shouldn't take things at face value, especially what the marketing droids tell us . Of course we all know that anyway don't we, and why, and how to spot it every time . Just digging for diggings sake has it's rewards too . Observing a good navey at his work, well a bit of that ethic can rub off . Good stuff TP :thumbs: From what I got the gist of, overclocking will still not be adversley affected by the thermal compound you use, the smear and the surfaces (and how close you can get them) will . So, there's a very good reason for the fearsome clips and springs that clamp our shiny bottomed, expensive, heatsinks down on the CPU other than the fact that every now and again the machine is going to get a boot across the room :badpc: |
Murray P (44) | ||
| 304501 | 2004-12-22 19:03:00 | Dead right Murray . Since the temperature drop across a THIN film of thermal grease is about 0 . 1deg C for high conductivity greases and say 1 deg C for white paste at 70 Watts, then no matter how much you overclock the thermal grease is not going to make any significant difference . The contact conditions are important, and so is the heat transfer coefficient or thermal resistance of the heatink . Many of the exotic HSFs quote very low thermal resistances like 0 . 2 C/W as against 0 . 5C/W for more stock units, but when you look at the noise, those figures are achieved at round about 50dbA, ie very noisy, too noisy for a normal person to endure . If you are trying to get rid of 70 watts at 0 . 5 C/W then the temperature rise will be 35C, and with an exotic unit going full bore it will be 14C . The basic physics cant be denied by wishful thinking or inaccurate temperature read out . Actually I'm not at all interested or concerned with overclocking . I mean if you wait a year you will get a cpu that is twice as fast as last years souped up overclocked cpu with shortened life, and which people then try to off-load on TradeMe :D Also Im only concerned at this time with AMD Athlon XP, so like has to be compared with like . Im also concerned with the accuracy of motherboard temperature readouts . |
Terry Porritt (14) | ||
| 304502 | 2004-12-22 20:22:00 | Actually I'm not at all interested or concerned with overclocking. I mean if you wait a year you will get a cpu that is twice as fast as last years souped up overclocked cpu with shortened life, and which people then try to off-load on TradeMe :D Well... I dunno about that... My Northwood P4 3.0 was bought at least a year and a half ago... basically when it was the brightest, shiniest thing I could lay my hands on... it can clock quite nicely to 3.5 with a little tweaking, and a year and a half later, clock speeds haven't sent this little beaut into the lower end of CPU's yet! As for your points, I guess what I'm saying is that I don't think your results were that surprising to me. Thermal paste isn't going to magically lower the standard temp at stock speeds, or while the CPU is at idle. I'd also question using just one type of CPU too! To prove the test, I would've loved to see how the Prescott chips fared. Oh, and also under stress would've been nice too... like a CPU burn in test through Sysoft Sandra? At the moment, the test looks like comparing the performance of a car running on LPG vs a car on 98 octane - but instead of measuring performance, etc, you are measuring them while their engines are idling and aren't moving anywhere! Good work on the calculations side of things though... lots of numbers which didn't mean a lot to me! ;) Lo. |
Lohsing (219) | ||
| 304503 | 2004-12-23 06:12:00 | At the moment, the test looks like comparing the performance of a car running on LPG vs a car on 98 octane - but instead of measuring performance, etc, you are measuring them while their engines are idling and aren't moving anywhere! Good work on the calculations side of things though . . . lots of numbers which didn't mean a lot to me! ;) Lo . You have to establish a basis for your tests before you can start looking at variables, of course the test has to be designed to exclude as many variables as possible, or be altered and re-measured as it progresses to exclude them . The idle speed that Terry chose is arbitary, he could have chosen full blast, overclocked or whatever, as long as all were exactly the same so that results could be compared . However, I suspect that it is easier to get consistency, without the influence of of benchmarking software, by testing at idle, less effort required and less danger of damaging the CPU . It's still a measure of the "performance" of the object of the study . The beauty of all good studies/theories/evidence, is that counter arguements can/(must) be forewarded, try to disprove it rather than prove it and you can't go wrong . Even if you do disprove it you have gained something . Prove it (in your own mind) and your study is likely to be invalided, sooner or later . BTW, Intel are not going for increased clock speeds to increse the "power" of their CPU's so much as they're increasing cache and cores . |
Murray P (44) | ||
| 304504 | 2004-12-23 06:46:00 | I see PF1 is back on line good oh . Murray is right again :thumbs: Neither the thermal grease, nor the heatsink know if you have overclocked :lol: All that we are concerned with in these tests and considerations is the amount of energy/second in watts that is coming out of the cpu and through the thermal grease into the heatsink . The more constant that is the better for purposes of comparison and calculation . We hear a lot of figures bandied about without the benefit of background detail and conditions of measurement . So there is a lot of cross talk . All I'm trying to do is to bring in a bit of science and rational thinking, rather than 'wild' statements . The thermoucouples arrived today! I had forgotten that drilling through the centre of the heatsink would hit the spring clip . So what I've had to do is make up a small drill jig to drill a 1 . 2mm hole at 45deg to the surface of the heat sink, so that the thermocouple wires can be brought out through the fins to one side of the clip . The AMD heatsink has a 3mm removable copper base and I've driiled that 0 . 6mm diameter in the centre to take the thermocouple . The thermocouple has been calibrated in crushed ice/water for the ice point and in steam corrected for atmospheric pressure for the steam point . Purified Water BP was used, all very scientific :D Stay tuned for more results . |
Terry Porritt (14) | ||
| 1 2 3 | |||||