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PT100 and PIC A/D port

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fuzzzy

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pt100 pic

Hi,

In your opinion which is the best way to interface PT100 to an A/D Pic16f876 port?
is there any IC suitable? how can I filter PT100 signal to have a good temperature sensor? is there any trick?
 

pic pt100

The PT100 has its ΔR/°C≈0.385Ω/°C
Your PIC has 10-bit A/D, what represents 1024 levels (≈0.0049mV per level).

If feed PT100 from ≈12.72mA constant current source you will have exactliy 1°C resolution. Is this what you are after?
 

pt100 schematic

so i don't need any kind of filter? can i connect pt100 directly to pic? this is what i wanted to know.

where i can find a good schematic of contant curren source for pt100?

Thanks for your help
 

pt100 application note

Check this paper.
Check www.analog.com application note AN-709
and microchip application note AN-687
 

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    fuzzzy

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pt100 microcontroller

To connet PT100 you PIC A/D input you don't need a special filter. Just use, say, 10µF tantalum capacitor and 5.1V zener diodr in parallel with the PT100 sensor/A/D input pin. Temperature doesn't change in µ or ms time (10µF cap) and 5.1V zener will protect the input against open circuit (voltage from constant current) ..

Added after 15 minutes:

As costant current circuit you can use LM317L voltage regulator. Here is its data sheet:
**broken link removed**
On page 9 you will find precision current limiter ..

Good luck ..
 

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    fuzzzy

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pt100 interface

For P100 constant current very important.Must be use a/d referance and current same source.If current source be dependent temperature all measurments wrong.Pls read analog device application note.
 

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    fuzzzy

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pt100 con pic

That is very true what you said, and I read ANs from ANALOG, but you from your 1st post you indicated that the A/D conversion will be done by a PIC and this microcontroller has only 10-bit resolution.

Voltage drifts of voltage regulators such as 317L (7805, ...) lay much below 10-bit resolution level, so you can safely use them as voltage/current refereces..

Different story with 16-bit, 18-bit or 24-bit A/D converters..
There one have to be very careful what one uses as voltage or current reference source..
 

My pt-100 giving triuble, whene i measure it with ohm meter it's resistance changes with temperature(30degree C normal room temperature, pt-100=25ohms)
but when i connect it in sires with 200ohm feeding with 5volt, pt 100 show 0ohms!!!!
and resistance not change with temperature.

Whats d problem?????
 

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