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abm.ben
Joined: 02 Sep 2008 Posts: 4
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Problème - AD7711 |
Posted: Tue Sep 09, 2008 7:50 am |
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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:
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-Pour 10°c .... SDATA=0x810DF3
-Pour 40°c .... SDATA=0x812BB9
-Pour 120°c .... SDATA=0x817AE0
-Pour 140°c .... SDATA=0x82651E
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FvM
Joined: 27 Aug 2008 Posts: 2337 Location: Germany
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Posted: Tue Sep 09, 2008 12:59 pm |
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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. |
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abm.ben
Joined: 02 Sep 2008 Posts: 4
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Posted: Wed Sep 10, 2008 6:45 am |
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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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