Trouble with the AD7714 Delta Sigma Converter 1

[professor]

Is anyone using the Analog Devices 24 bit A/D converter AD7714 and experiencing problems?<br>
<br>
Zero/Span shift after time?<br>
<br>
Date Code specific differences?<br>
<br>

 

I have been using the chip AD7714 since 11,1999 to now,what I found was that it can not achieve 24bit AD conversiuon with gain 1 at f=12.5 . The output noise from 7714 reached 30uV p-p.So I have to used a AD620 just before AD7714' inputs,and use a 4066 to control the gain of AD620

 

[PeterClaassen]

Hi Proffessor, it seems you have had more succes with AD7714 than I had. I have it connected up to 8051. configured AD7714 bipolar, chan1&amp;2, gain 1. Signal from 0Vdc to Vref(pot) on AIN1, AIN2 0Vdc. I get the same reading
on all channels,(even AIN6, which is internaly shorted.)
AIN3-5 floating. Reading is 08399820(FS) to 08400160(ZERO) on all channels. What am I doing wrong?
Thanx in advance!!!

 

I am writing a driver for the AD7714 to measure low
level voltage and resistance inputs (TC + RTDs). I am
pretty sure that I am using the device OK but are
getting some unusuall conversion values. I have a
calibrated input source of 1v on channel 2 (fully
differential) with the AD7714 working in bipolar mode
with a vref of 2.5v. The conversion value just seems
to be incrementing slowly.

Has anyone a small piece of c code for driving the
AD7714 - ideally with the 68HC12.

 

[cbarn24050]

hi, you can find the code you need at

http://www.analog.com/library/applicationNotes/dataConverters/PDF/AN-406.pdf

 

[RayRogers]

Hi, should follow the advise in the application note; but
there are some things to consider. Check your system with a &quot;known&quot; input over a long period of time. Almost all systems will exhbit 1/f noise. Self-calibrating systems should move the 1/f knee out beyond 6 months. You will not know unless you generate a time series and do a FFT and PSD. You also should check your system out with some form
of an enviromental chamber. We should all attempt to implement very accurate and stable systems, but you don't know without actual testing. The chamber doesn't have to
be fancy; if the sytem is really stable then it will not matter whether you test to 40degC or 50degC. It will read the same (as long as your referance is stable/outside). The cheapest tests are shorts and Vref; but you need to
put forth a little extra effort to have believable results.
And don't forget some humidity testing at these voltage
levels.
As I said, these tests can be really primitive if the system
is really stable. Acquiring compensation values would require precision in the testing.

 

hi, i have a problem, i wire the AD620 with a digital potentiometer, but it doesn't work, someone have any why?
lgodoy_ve@yahoo.com