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'[PIC]: temperature'
2002\09\17@094657 by llile

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Topic Tag changed to [PIC]:

Thermocouples are going to be very hard to read directly with a PIC.  They
generate nonlinear millivolt level signals.  You will need a thermocouple
amplifier, and you will have to pay special attentio to the materials used
to connect to the thermocouple, and maybe even to the temperature of your
thermocouple amplifier!

However, at 1200C, you have very few choices in temperature sensors.
Thermocouples are almost the only thing you can use at such temperatures.

I assume you have a chart converting the millivolt output of the
thermocouple to a voltage.  Your thermocouple amplifier will amplyfy and
scale that voltage, but it will probably still be nonlinear.

At that point you have two options, math or a lookup table.  The math to
convert a thermocouple reading to a temperature is doable, but complex. It
may well exceed the capacity of the 16F872.    The lookup table is a
software equivalent of the thermocouple table I mentioned earlier,
multiplied by the gain of your thermocouple amplifier.  The size of the
table depends on the accuracy you want, and how good you are at writing an
interpolation algorithm.

All in all this is not a trivial task.  I hope you've got some PIC
programming under your belt already.


Having said that, Maxim makes a thermocouple- to- digital chip with 10 bit
resolution and an on-chip temperature compensator that could probably
solve your problem in one whack.    It uses Type K thermocouples, which
are good to 1250C, maybe not hot enough for you.  Looks like the chip
won't handle much above 1000C.  Look around, there are others like this
that may work for you.


MAX6674/MAX6675



-- Lawrence Lile





Dimitar Jelew <spam_OUTpf872TakeThisOuTspamHOTMAIL.COM>
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09/14/02 05:18 AM
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       Subject:        temperature


Hello,
I have a problem converting temperature values
Well I need a way to convert temperature values
to 1200 degreez celsium .It is with termocouples
and pic16f872 microcontroler
I need you ways for converting such values.
Thanks  a lot!

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2002\09\18@125931 by Alan Shinn

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Chromel-Alumel thermocouples  from CRC handbook
100  =  4.10 mV .041 mV/deg
1000 = 41.31 mV .039 mV/deg
1100 = 45.16 mV .038 mV/deg
1200 = 48.89 mV .036 mV/deg
1300 = 52.46 mV .035 mV/deg

These are referenced to a 0 deg cold junction - just add ~25 deg for
room temp operation.
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Looking forward:
Alan Shinn


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