Built-in temperature reading accuracy?

pivotal · Post by **pivotal** » Wed Nov 02, 2005 3:22 pm

Hey chaps, I've been lurking for a while and I've finally got a question to ask:
How accurate are the built-in thermal probes in motherboards and CPUs?

The reason I ask is that I've built a new PC for the first time in a while, and I've got it pretty nice a quiet with a Zalman 7700cu on the AMD64 3200+ CPU and an Arctic Cooling VGA cooler on the 6600GT graphics card.

I've got one Zalman temp controlled 120mm extracting heat from the rear (I've unplugged the case's stock 120mm fan in the front, because it isn't variable speed), and a el-cheapo 520W PSU with a nice quiet 120mm fan in it.

SpeedFan is reporting 22-25 degrees C at the CPU on idle (ambient is around 17-20 degrees C), and the BIOS says the same thing. The CPU doesn't go above 40 (MAX) under gaming load.

This is with the Zalman CPU fan running inaudible at 900rpm, and the case fan barely audible at 1300RPM.

It almost seems TOO cold for the CPU. I don't want to complain, but I've NEVER had a modern CPU run that cold. Should I just shut up and overclock it, or should I be concerned enough to grab an IR temperature probe for testing?

Cheers!

GlassMan · Post by **GlassMan** » Wed Nov 02, 2005 5:15 pm

they are almost always inaccurate, but if the chip is venice, it isn't far off. A very cool chip.
My 3700 san diego @2800 folds in the low 40's, (by probe to side)

Elixer · Post by **Elixer** » Wed Nov 02, 2005 6:41 pm

Yeah, reported temps can be off by quite a bit. + or - 10 degrees even. Your temperatures sound like they're reading lower than they actually are. Just one more reason why stability is often a better check of a computer than temperature.

Live · Post by **Live** » Wed Nov 02, 2005 7:24 pm

Intelligent thermal management is the key to silent computing, but CPU temperature reporting mechanisms are inaccurate, with results that can vary by 10°C or more. The causes are complex, but correcting them to a more reasonable margin of error is not terribly difficult.

Calibrate Your CPU Temp Reporting

=assassin= · Post by **=assassin=** » Thu Nov 17, 2005 9:59 am

Yeah, if it is a Venice or Winchester core, then those temperatures are likely for that ambient temperature - maybe only a couple of degrees off. The latest Athlon 64's really do run that cool, and in some cases, cooler!!

If it's a newcastle or clawhammer, I'd be a little suspicious and would err on the side of saying the sensor is a little out, but really, if it's stable there is nothing to worry about.

Post by **CA_Steve** » Thu Nov 17, 2005 9:47 pm

the thermal diodes in the CPU, GPU, etc as well as the temp sensors used on the boards can have an accuracy of anywhere from 1C to 4C, depending on the design/device selected. Plus, as Live pointed out with the link, just because there's a diode on the CPU that's used to measure temperature, it doesn't mean that's the highest temp on the CPU. It's just the temp in that silicon neighborhood.