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Thread ID: 52362	2004-12-17 04:49:00	CPU temperature results	Terry Porritt (14)	Press F1

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304485	2004-12-17 04:49:00	Thought I'd report on some cpu temperature testing, it isn't that scientific but could be of interest . I bought the following, A DSE case with 3 built in temperature probes and front read out, an el cheapo MSI KM4M-V motherboard with onboard video/sound, An Athlon XP 2400+ 266FSB cpu with stock AMD heatsink and fan, A Thermaltake Volcano 11+ Xaser heatsink and fan with fan speed control options . I also lapped the copper base of the Volcano to improve surface finish and flatness . Flatness is estimated to be within a light band or two . I opted to use the manual speed control for the Volcano . First of all I checked the DSE temp . probes against a Fluke thermocouple/digital multimeter, with all in a glass of warm water at about 45deg C . The probes all agreed to about 2 deg C . The Fluke had been checked a long time ago against the ice point and in boiling water . I mentioned in an earlier posting that the AMD heatsink surfaces were not flat, and that I lapped both sides of the plated copper base plate and the surface of the aluminium heatsink to a reasonably high degree of flatness . One DSE probe I taped to the cpu next to the core using 'thermal tape', one is dangling in the case and one is positioned at the front air inlet to a 120mm case fan . (There is another 120mm case fan at the rear) . A program called PCAlert came with the motherboard, and this displays cpu temperature as reported by the BIOS from a thermal diode in the cpu core, system temperature from I dont know where, and cpu fan speed . I have 3 different heatsink thermal compounds: Titan "silver" grease from DSE, which is not silver but probably aluminium particles/flakes in a silicone grease base . This has a very nice soft consistency enabling a very thin film to be applied; Arctic Silver 5, 'polysynthetic silver thermal compound', this is rather stodgy and a stiff backed razor blade seems the best way of applying a thin film . The greyish colour of the silver also suggests that it is silver oxide rather than pure metallic silver . The third compound is a white silicone grease that came with the Volcano, and it says Silmore-Taiwan on the packet . The blurb with the Volcano says Dow Corning T340 . I have tested both heatsinks each with all 3 thermal compounds with Windows XP running 'at idling' . Now the Volcano noise is just not tenable with the fan running flat out at 4800rpm, the quoted noise level says 48dB, and 17dB at 1300rpm . I found 3000rpm gave just about acceptable noise, so that was the speed for the tests . OK, so after all that preamble here are the results: NO significant difference in cpu temperature between either of the heatsinks or the thermal greases . :eek: Typical readings are: CPU temperature (from the thermal diode),54 deg C; System temperature,25 deg C; Ambient air temperature 20 deg C . With Volcano fan running at max speed, cpu temperature 52deg typical, 25 system and 20 ambient as above . That is only 2 degrees lower than at 3000rpm The DSE probe attached to the cpu next to the core reads typically 15deg C less than the core thermal diode . Now Thermaltake publish a cpu temperature rise against watts dissipated curve for the Volcano 11+, which says at 70 watts the temperature rise is 24deg C . So, if the fan is at max speed, the cpu temperature should not be above 44-49 deg, and really somewhat less as an idling 2400+ will be at about 60/65watts? So what does all this mean????? Well, if the heatsink surfaces are really flat, and have the finest surface finish possible, then the real area of metal to metal contact is maximised, and only the faintest trace of heatsink compound is required . Under these conditions the thermal grease film is essentially isothermal, ie no temperature difference across its thickness, and so the results confirm what I had suspected: viz . that you can use any old thermal grease . The stock standard AMD heatsink and fan is also more than adequate, and of course costs little when you get a 'retail' boxed cpu . The proviso is that it needs working on to provide much better flatness and finish, something not everyone can necessarily easily do . The other significant aspect is the difference between built-in thermal diode temperature, and that obtained from a probe against the cpu case . Some boards have a thermistor inside the socket, and it is meant to be bent up to contact the underside of the cpu . I have this on my Abit board, again I suspect that the 'real' core temperature is about 15deg higher than the reported 42deg typical for Athlon Thunderbird 1 . 33Mhz . Now before anyone starts claiming their cpu runs at 35deg C when the ambient air is 20deg or more, just stop for a moment and think about the physics .	Terry Porritt (14)
304486	2004-12-17 04:57:00	What are you playing at, Terry? Bringing facts in to spoil a subject which is full of good "theories", even better opinions, and faith in advertising . Disgusting . :eek:	Graham L (2)
304487	2004-12-17 05:47:00	What are you playing at, Terry? Bringing facts in to spoil a subject which is full of good "theories", even better opinions, and faith in advertising . Disgusting . :eek: Too b****y right Graham . For a start this thread should have been posted in the Chat forum Mr Porritt, more appropriate to what the typical post will be, ah hum, including this one :D The other thing we can say for sure from this evidence is, the Thermaltake HSF is pile of overblown, noisy junk . One more thing, we'll have to find a way to drop your CPU in that glass of warm water along with the other measuring devices while it's at idle . I think I've already solved the dropping in the glass bit, someone else can work on the, while it's idling bit, ok . PS . The rest looks fine, excellent work :@@:	Murray P (44)
304488	2004-12-17 06:00:00	well....as long as each setup was given three days use in order for it to show what its longterm running temp will be(they can drop by 15 degrees in the first 3 days after a new install),and that the probes were tested for reliable readings up and down the temperture spectrum and not just in 1 glass of water,that room temperture and case temperture were contriolled so that each test had an equal base,and that the system was tested at idele,and at work,half load,full load and a few hours sustained load would do the trick. Would also be a good idea to see how each setup operates in poor conditions,such as a hot room,or a poorly ventilated case. Besides which,rather then machinging the bottom of the heatsink its far easier to rub a small out of paste into the surface to fill up the irrglarites and then wipe off the excess,resulting in getting a perfect contact with the cpu.....which of course only gets a razor thin covering......	Metla (12)
304489	2004-12-22 02:45:00	I was going to post further on this topic when I had some thermocouple readings from the contact surface of heatsinks with the cpu die, but it looks as though the thermocouples on order wont now arrive before Xmas . So here are some further simple physics sums to explain some of the strange statements surrounding cpu temperatures and thermal compounds . Let us take the very basic steady state heat conduction equation, and we will take this as read, you can all look it up in school certificate physics, or any Engineers Diary, Machinerys Handbook, or even the internet, or whathaveyou . Q=K . A . ΔT/ΔL Q is the steady rate of heat conducted, Watts; K=thermal conductivity, Watts/metre . deg C; A =area through which heat is flowing, metres^2; ΔT temperature difference deg C over a length ΔL metres . Let us look at two thermal compounds, white generic Dow Corning T340 silicone thermal paste, and Arctic Silver5 silver compound with "polysynthetic oil" base and 88% thermal conductive filler . The thermal conductivity of Dow Corning T340 (from interner search) is quoted as 0 . 73 Watts/Metre . degC . The thermal conductivity of arctic silver translated from the crazy American system of mixed units on the Arctic Silver website comes out at greater than 8 . 9 Watts//Metre . degC {When I say crazy units they are mixing metric system watts and metres with inches . That doesnt give much confidence in their figures or credibility does it? But that is all we have to work with, and the 'greater than' comes from their site too . } The particle size for the conductive filler in Arctic Silver is said to be 0 . 49 micron, a micron is 10^-6 of a metre,ie a millionth of a metre . So the absolute minimum thickness of Arctic Silver that you could have between two perfectly smooth surfaces is say 0 . 5 μm Now real surfaces have hills and valleys, ie a surface finish that can be measured with a surface texture measuring instrument like a "Talysurf" . The smoothest most common engineering surfaces belong to gauge blocks, or slip gauges, as any toolmaker can tell you . These are precise length gauges that can be 'wrung' together, and any residual film between the surfaces will be less than 0 . 02μm . So to consider thermal compound film thicknesses of 0 . 5-1 . 0 μm between the polished surfaces of a cpu die and a heatsink is quite reasonable . The other characteristic of metal surfaces is the small real area of contact as opposed to the apparent macro area of contact . It can be as low as one hundreth of the apparent area of contact . It is this factor which goes to explain why the classical Amonton law of friction gives a friction force dependent only on loading and not on area . But of course they didnt have gauge blocks in Amontons day . {Anyone who wants to do more research into the physics of surfaces in contact, and the real area of contact could start with reading the classic work of Bowden and Tabor, The Friction and Lubrication of Solids, around 1950, with later reprints and additions} OK, SOME CALCULATIONS: Consider a film of thermal compound separating the cpu die and the heat sink surface . Im going to assume very smooth lapped surfaces so that the amount of compound in the surface texture is small . For the sake of the calculation let the film thickness = 1 . 0μm Let the rate of heat transfer=70 watts . Let the die size = 11mmx7mm, the size of an athlon XP 2400+ this equals 7 . 7x10^-5 square metres . For Arctic Silver the temperature rise across the thermal compound is ΔT= 1x10^-6 x 70/7 . 7 x10^-5 x 8 . 9 = 0 . 1deg C For Dow Corning white thermal paste the corresponding temperaure rise would be: ΔT = 1 x 10^-6 x 70/7 . 7 x10^-5 x 0 . 73 = 1 . 2deg C So there is about a 10:1 ratio between the two compounds, but since we are only talking of ~1deg C for white thermal paste this would hardly be measurable given the variabilities between operating setups even in the same computer . This confirms my measurement of no significant difference between compounds . NOW, we come onto the the Arctic Silver statements and that of Metla, that after a period of time the cpu temperature drops . Arctic Silver say 2-5deg C after about 200 hours, Metla says upto 15 degC after 3 days . How can this be explained?????? One thing is sure, the composition of the thermal compound is not transmogrified by alchemical means into a different wonder substance . :D No, any cpu temperature drop can only occur by increased heat transfer through the compound and into the heatsink, and this can only happen by the thickness of thermal compound decreasing with time . So what thickness change will bring about the quoted temperature drops?? For Arctic Silver5 For a Δ(ΔT) of 5deg C, the corresponding change in compound thickness works out at 0 . 05μm, (thats 0 . 002 inches or 2 thou for those that like inches) . Whereas if we take the change of 15degC quoted by Metla, then the compound thickness would have to decrease by 3 times that or 0 . 15mm (an incredible 6 thou) :eek: That would suggest the compound has been trowelled on . Obviously if the surfaces are lapped quite smooth and flat (and the cpu die already is, you cant lap that, you would just make it non-flat), then only the thinnest film has to be initially applied, a film ideally that is 0 . 5μm thick (it cant be thinner), or say 1μm, and NO cpu temperature drop over time will be observed because the film is already as thin as it can ever get . QED . On the other hand if the heatsink surface is very rough, and we only have 1/100 of the apparent area in contact, then most of the compound will be in the valleys of the surface . The peak to valley depth will be many times the thickness of the compound at the asperities, and the temperature drop across the interface will increase as the surface roughness increases . To carry more rigorous sums we need to be able to estimate the real area of asperity contact between clean surfaces under Hertzian contact loading, and to estimate the mean surface texture depth that will be filled with compound, as far anyway as a compound particle diameter of 0 . 5μm would allow . This could be done with extensive effort with a Talysurf and statistical analysis, and I have done similar in the past, but it aint worth the effort . Now the another point Metla raised was carrying out better temperature probe calibration over a range of temperature . It just isnt worth it . Two points is enough, room temperature which I didnt mention but assumed people would realise that, and an elevated temperature around the temperaure of interest . Else the ice point, and the boiling point of water could be used for accuracy . These probes are linear enough for our purposes, if they werent they wouldnt be any good would they? So in summary, the better the surfaces in flatness and texture the better the heat transfer because the thermal compound can be very thin, ~1μm or less, and differences between compounds are not really that significant . If any significant drop in cpu temperature is observed over time, then it means the compound was applied too thickly to start with . What I plan to do next is to drill through the AMD heatsink at the centre of where the die comes, normal to the surface and bond in a thermocouple with the end dressed flush with the surface, and the surface lapped 'flat' . This will measure temperature directly at the die surface . The heat transfer will be reduced slightly because of the hole diameter . Hopefull report on this in the new year .	Terry Porritt (14)
304490	2004-12-22 02:53:00	Wow Terry! I was lost half way... but you could probably pass a PhD with this! :D	~sy~ (95)
304491	2004-12-22 03:30:00	Oh gosh a bad typo: >>>For Arctic Silver5 For a Δ(ΔT) of 5deg C, the corresponding change in compound thickness works out at 0.05μm, (thats 0.002 inches or 2 thou for those that like inches). That should read 0.05mm NOT 0.05μm Sorry about that it makes a world of difference.	Terry Porritt (14)
304492	2004-12-22 03:35:00	Whoa . And stop quoting numbers i pull out of thin air . . . Anyhow, It will be interesting to see what results you come up with from the next stage,You should seriously consider having this work published on a site somewhere . Wonder what Whetu makes of it . For what its worth,I don't use Artic Silver,I use their ceramic paste, And near every comp I build sits at about 30 degrees as reported by the inbuilt hoodacky whatsit .	Metla (12)
304493	2004-12-22 04:04:00	That is some great scientific work you have done there Terry, the second stage of your investigations should be interesting as well. This article is just in time for my annual summer paranoia about my CPU temperature .. :rolleyes:	Jen (38)
304494	2004-12-22 04:28:00	This article is just in time for my annual summer paranoia about my CPU temperature .. :rolleyes:[/QUOTE] This year we may not get the summer thing, or may allready have had it, judging buy the last week or two. D.	drb1 (4492)
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