SUMMARY: Testing CPU heatsinks using motherboard temp sensors may be possible, but the probability of unintentional errors is high. A more rigorous testing regime using thermocouples and digital thermometers is the "gold standard".

I have been working with Andy Lemont at Millennium Thermal Solutions on heatsink testing. Andy believes that many of the reviews you see by various hardware sites are well meaning but unintentionally mis-represent the true performance of many heatsinks. This can be traced to the imprecise measuring tools we use, most notably motherboard temp sensors.

Coincidentally, Stephen Hoar at Burning Issues has written a very interesting article (What's a review worth? ) that examined this in some detail. Andy Lemont summarized Stephen's "review of reviews" in the following graph:

Stephen used Global Orb tests in this analysis. According to Stephen, some Global Orb tests miss the mark by over 100%; this means that a review temp of say 30C is actually more like 60C! One key point is that

"For some reason, maybe due to calculator-allergies, you don't see °C/Ws-a figures in the innumerable fansink tests posted up on hardware sites. It's a pity, because this is the only measure which might be called a fact, & is of real use to every reader worldwide."

I think the dilemma reviewers face is to test CPU cooling in a way that users can affirm on their own systems. For example, Tillman Steinbrecher over at Anandtech just did a heatsink roundup (Socket-A & Socket-370 Cooler Roundup - November 2000) using

"...an Abit KT7-RAID motherboard, a Thunderbird-750 CPU (overclocked to 950MHz using 1.8V voltage), an Asus V6800 graphics card (GeForce1), and 256 MB PC133 RAM. We used an Asus/Elan Vital midtower case and an Antec power supply...The temperature measurements were made using the KT7's onboard thermistor..."

Using the KT7's socket thermistor raised issues that are covered in the following thread in Anandtech's Forum. Basically I think it boils down to the following (arguable) points:

• Motherboard sensors are inherently inaccurate and not suitable for testing heatsinks;
• Boring small holes in heatsinks and inserting thermocouples is one acceptable test method (this is an Intel spec);
• Measuring CPU temps using a thermocouple on the back of the CPU is possible and can give accurate results if properly set up.

• Attach a "T" type thermocouple to the backside of the CPU, directly under the core;
• Insulate the socket to avoid any "trapped air" interference'
• Use a calibrated digital thermometer (in my case, Omega HH23);
• Use another thermocouple to measure ambient air temps;
• Report absolute temps, motherboard sensor temps and calculate C/Ws.

Andy is developing a heatsink (AAGK-1 ) and, of necessity, must test it against others (BTW: typical engineer - calls it the "AAGK-1"; I call it the "ice cube"). We hooked up and started talking about the testing issue. It turns out that Andy's office is less than an hour from me, so I visited a couple of times; we proceeded to do a test comparing a bunch of heatsinks using lab methods and on an ASUS A7V and ABIT KT7.

Now let me be the first to say Andy is out to prove a point here - that his heatsink is among the best around. In the tests that followed, I participated with Andy and have no reason to doubt what we found. However, this is about is heatsink testing - any future heatsink reviews that I perform will be on my premises with the equipment I outlined above.

Go to PAGE 2 for the Lab Setup.

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