Peter McNulty wrote:
> Hi,
>
> What temperature sensors would you recommend for:
>
> -Fast Response Time (90% of actual temp)
> -Relatively Cheap (This is a school project, so nothing that costs
> $100)
> -EASY to program for using PIC16F877 - This is a must! Themistors are
> looking to be very difficult to program for, for a nice accuracy
> -Accuracy of sub +- 1degreeC
>
> I've looked at the LM335 solution, but the response time is very long
> compared to other things, and so is the maxim chip. I've also messed
> around with thermistors, just printing out an ADC value and they seem
> to vary the most, but they are hard to program for as they are
> non-linear, and they change over age. RTD's look good, but i can't
> get a definate price on these things yet, and they are linear with a
> fast response time. Thermocouples I haven't really thought about,
> though i don't know if  they have thermocouples for the range of -50C
> to 100C with a nice accuracy, fast response time and easy
> programming. Are thermocouples linear?
>
> Are there any other solutions i haven't thought of? What are your
> opinions of solution i need?
>
> Thanks
> -Peter

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}

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