Temperature Sensors

[sviola]

Well, hope I'm posting in the right section.

I'm interested in acquiring a few thermal sensors and an lcd and am going to do my own temperature acquisition system.

My question here would be where is the best place I could set the thermal sensor on the cpu and gpu. Should i "glue" (stick with adesive tape or other method) them to the heatsink of each one? Or should i fix them using the pressure done by the heatsink on the processor?

 

[maury73]

Simply don't do that

Sticking temperature sensors on the chips or (even worse) heatsink will never give you the right temperature. The temps stated in datasheets and manufacturer's reccommendations are the "die" temperature, that can only be accurately acquired with internal sensors.
Of course it's possible to read them even with high precision using very good thermistors, but you also have to know exactly the case-to-junction thermal resistance of all the components your want to monitor and the case internal temp with at least 0.5°C precision.

If you don't have such data you'll never get the exact internal temp and you may get erratic values because the internal temperature rises more than the case temp at high power consuption, they dont' grow linearly.

 

[maury73]

Even with internal sensors the reading are not accurate. The temp readings you get in the bios are all interprated by software and the software isn't accurate

The user didn't speak of reading from BIOS, but with an external circuit with LCD.
The problems is neighter the sensors (they can assure 0.2°C accuracy with the right algorithm and a good converter) nor the software that can be very accurate (you simply need to use more bits).
The only limitation is the T/V (temperature/voltage) ADC converter that is mounted on the mobo: they are very cheap models so they have very poor accuracy (up to 10°C error).
With an high precision T/V ADC with absolute reference you can measure temps up to 0.2°C precision with a normal embedded diode, the problem is it costs about 10$ per channel while those used on mobos cost 0.5$ per channel!

 

[antoant]

If you want accurate readings then the closer you are to the chip the better. The best way to get close to the chip is to make a little notch on the heatsink and place your sensor in there. Make sure that the sensor and the heatsink surface are flash so that good contact is made between the heatsink and the chip. (You do not want that new CPU melting down on you).
From there on it is all about calibrating the sensor to give accurate values. And since you are trying to make your own system I will assume you already know how to calibrate the sensors.

Good luck with the project, it sounds cool but I don't see the use of it other than the fact that is cool.

 

[antoant]

I do agree that the procedure I suggested will reduce the effectiveness of the heatsink although the percentage of the decrease could be negligible. As far as imperfections on the surface of the heatsink is concerned, if done properly and with care, the final result could be as flat of a surface as before.

Placing the sensor in the gooves of the HS right over top of the chip will give you accurate enough readings.

Well I don't know about that. It all depends on how you define accuracy. For you a couple of degrees up ro down might be fine but for the OP that might be unacceptable.

Now I am not picking on you I am just saying that each method has its advantages and disadvantages.