Temperature sensor - MC9S08DZ60

[jesortsan]

Hi,

I need to control the temperature level in my system in order to activate/deactivate several fans. The system is located inside a rack box (450 x 350 x 36 mm approximately). Do you think the temperature sensor inside the microcontroller (MC9S08DZ60) is enough to carry out this task? Or it would be better to use an external specific temperature sensor?

Thanks

Message Edited by jesortsan on 2007-03-1901:26 PM

[YeOldeBDM]

Putting aside the details of using the references inside of the micro to measure temperature, you have to experiment to answer your question.

The micro has some degree of self heating, and imho, is going to measure board temperature alot better than air temperature. So dont put anything dissipating significant power next to it. Also, you can be sure that the temperature measured by  the chip will significantly lag the temperature of the air around the chip (and, like I said before, probably will be more board temperature than air temperature).

This makes the control loop design totally interesting. (Im using 'interesting' in the Chinese sense).

[bigmac]

Hello,

To add to the previous post, if you need to control a fan to cool the MCU itself, the internal temperature sensor is ideal.  However, for general cooling of the inside of the enclosure, where other major heat dissipating components are present, you would either need to predict the internal temperature rise of the MCU above the surrounding ambient, and make allowance, or minimize the self heating of the MCU - maybe a combination of both.

For negligible self heating, the MCU would need to operate in a low power mode for the majority of the time, and the temperature would need to be measured immediately after wake-up.

I also agree with the previous post, that you would be prediminantly measuring the temperature of the board, and that the major heat dissipating components should be kept well away from the MCU.

I presume you would use a simple on/off control scheme (with hysteresis), rather than proportional control.

Regards,

Mac

Message Edited by bigmac on 2007-03-2001:40 PM

[jesortsan]

Thank you very much for your comments.

It's like I supposed (the temperature sensor on-chip is going to measure board temperature better than air temperature), but I wanted to collect some other opinions from more experienced people before taking any decision.

Thanks for your help

[Alban]

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jesortsan wrote:

Do you think the temperature sensor inside the microcontroller

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Hello,

Which µc are you talking about ?

This indication must also be in the subject line.

Thanks,

Alban.