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arunb
Joined: 08 Sep 2003
Posts: 492
Location: India
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| Using PT100 thermocouple for measuring temperature |
 Posted: Mon Jul 18, 2005 9:00 am |
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Hi,
I have a PT100 thermocouple (Two wire type). I want use the thermocouple to measure the temperature. I have a 16F628 mcu connected to a MCP 3208 ADC, I would like to use these and the PT100 to measure the temperature..
The mcu and the ADC work very well, but I do not know how I should connect the PT100 to the ADC...
Could anyone post a simple circuit ....please..???
thanks
arunb |
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Neutone
Joined: 08 Sep 2003
Posts: 839
Location: Houston
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| Posted: Mon Jul 18, 2005 9:34 am |
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| What you need is a simple voltage divider. I suggest you use a referance voltage around 5 V. Plan on a current at 0C of 1mA to prevent element heating. Using a voltage divider with a know resistance and voltage drops you can solve for the second resistance. |
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SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
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| Posted: Mon Jul 18, 2005 11:12 am |
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Are you sure it is a thermocouple? PT100 sounds like a platinum resistance temperature device (RTD). The platinum device is a resistor who's value varies with temperature. A thermocouple generates a voltage as a function of temperature. They way they would be connected to a PIC is very different.
If you measure the resistance at room temperature with an ohmmeter the platinum device should read near 100 ohms, a thermocouple would read much lower.
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The search for better is endless. Instead simply find very good and get the job done. |
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sseidman
Joined: 14 Mar 2005
Posts: 159
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| Posted: Mon Jul 18, 2005 11:15 am |
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| Neutone wrote: | | What you need is a simple voltage divider. I suggest you use a referance voltage around 5 V. Plan on a current at 0C of 1mA to prevent element heating. Using a voltage divider with a know resistance and voltage drops you can solve for the second resistance. |
That would work if the thermocouple were a resistive device  , but alas, its a voltage device. You're thinking of a thermistor.
Thermocouple amplifiers can get quite complex, as many employ cold junctions and the like.
I'd recommend a good google search for "thermocouple amplifier". Early on, you get pointed to a national instruments app note that seems helpful.
Scott |
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