At 03:03 PM 08/02/2010, you wrote:

>On Mon, 08 Feb 2010 20:48:26 +0100, "Dario Greggio" said:
>
> > This is a point indeed. I was planning on using a transistor as well,
> > coupled to a tiny SOT23 such as MCP9800. I can't actually think of
> > anything "faster" than a transistor to heat up, I mean... a lamp or a
> > resistor sounds slower to me...
>
>A hot wire exposed directly to the air is pretty responsive. The wire
>material is also probably a relatively poor conductor of heat, so the
>temperature is not heavily influenced by the connecting wire. As opposed
>to a transistor, encased in plastic, with copper leadframe and
>conductors muddling the accuracy by bleeding heat into the thermally
>isolated parts of the device.
>
>Cheerful regards,
>
>Bob

The key to this kind of measurement is to maintain the temperature constant
and look at the power input. This is the same idea as
running a photodiode from a reference voltage into the virtual ground of a
transimpedance amplifier (keeping the voltage across the diode constant)
and thus eliminating most of the effect of the PD parallel capacitance.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



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