Thanks for the recommendations everyone. It looks like I'll take the RTD
route as they are fairly linear, cheap, fast reponse time ( a couple of
seconds for 90% of temp), and they are easy to program for, only a little
bit of arithetic.

I only need a temp range of about -40 to 100 C so it will be fine for me,
however, if i extend this project for  higher temps, then it looks like i
might go with the Thermopile or possibly a thermistor ( eek)/thermocouple.

Thanks
-Peter
----- Original Message -----
From: "Wagner Lipnharski" <wagner@USTR.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, December 02, 2002 11:41 AM
Subject: Re: [OT]: Temperature Sensors?


Ray Gallant wrote:
> I would recommend a 100R or 1K platinum RTD.  About  $3.50 CDN.  You
> can get free samples on your own.  Spend your money on your front end
> and Vref accuracy.  Use a table derived from the available formulas
> for cold and warmer temperatures.  If you go that route check out
> DIN- EN60751 class-x and other standards.  The drift on some of these
> RTDs are minimum and if your circuit is very stable, you won't need
> to calibrate, just a verification is required.  You may need a DC
> offset due to the temperature range.  I use RTDs from Heraeus with
> great results.  You can also design a programmable home-grown
> temperature chamber (-30 to +30 deg C) for about 100 - $150 with a
> camper's cooler, darlington, relay & pic. Regards,  {slewrate}

The only problem with RTDs and NTCs is its top temperature.

The RTD Panasonic ERTD2FHL103S (Digikey $1.06) goes from -30 up to +1250C
only!!!

The NTC Thermometrics Global AL03006-5818-97-G1 (Digikey $2.66) goes
from -50 to +2040C (+4000F) only.
If you need to cook SMD, it needs to go at least to 4500F, obviously should
operate at least up to 20% more, or, around 5300F.

A THERMOPILE is a nice non-contact sensor, that can measure the temperature
away of it.
The MLX90247B (Digikey $13) in TO39 4 leads, generates 40uV/K and it
incorporates a 26 kohms PTC in the same die, so you can compensate ambient
temperature.  Even that operating temperatures should be from -40 to
+1500C, this is the thermopile temperature, not the reading non contact
temperature, even that I could not find its reading temp range.
http://www.melexis.com website can give you more details about this chip.
They also have modules with complete solutions, digital or analog output,
but be aware of their $65 prices.

VV46NER

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