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Problème - AD7711

 
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abm.ben



Joined: 02 Sep 2008
Posts: 4

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Problème - AD7711
PostPosted: Tue Sep 09, 2008 7:50 am     Reply with quote

Hello everyone!

I wish to make a system to acquire the temperature with a Pt100, to be made with an AD7711 interfaced with a PIC 18F258. I used the driver
"AD7710" provided on the topic,
http://www.ccsinfo.com/forum/viewtopic.php?t=28553&highlight=ad7710

I have made a test that did not go correctly. It gives me values which I
cannot interpret:
Code:

-Pour  10°c  .... SDATA=0x810DF3
-Pour  40°c  .... SDATA=0x812BB9
-Pour  120°c .... SDATA=0x817AE0
-Pour  140°c .... SDATA=0x82651E
FvM



Joined: 27 Aug 2008
Posts: 2337
Location: Germany

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PostPosted: Tue Sep 09, 2008 12:59 pm     Reply with quote

I guess, you noticed that the AD7711 has some programmable features, that must be enabled for Pt100 measurement, particularly exitation current. Also a higher gain than 1 is most likely meaningful. This doesn't require a new driver, just setting the respective control register bits.

I would also expect, that you did some precalculations, what should be a meaningful measurement in your application. We don't know either your exact circuit nor possible different control register settings already implemented and thus can't know, what may be a right or wrong measurement.
abm.ben



Joined: 02 Sep 2008
Posts: 4

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PostPosted: Wed Sep 10, 2008 6:45 am     Reply with quote

Thank you for your answer very fast.

what I have done is use the driver provided on the topic and put a resistor precision instead of pt100 and depending on the value returned I made the calculated temperature via an equation correct and well validated.

for everything that is setting the record control I have already changed the gain, activating the flow of excitement, but whenever the return values are wrong.

there is something that I did not understand in the driver provided on the forum is that in fact what the return record SDATA east of 32bit data while it would just over 2 bytes.

if your already succeeded in doing that. can have them communicate.

thank you.
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