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Subject: Re: Switching between analog inputs

Date: 01/03/02 at 6:58 AM
Posted by: HEMAL
E-mail: hemal@masibus.com
Message Posted:

In Reply to: Re: Switching between analog inputs posted by Hap on 12/28/01 at 1:10 PM:

Dear Sir,
I got the problem regarding dg406dj.I reaaly stuck & very much upset with this
problem. Kindly consider this problem very seriously & please send me
solution as soon as spossible. I send u more details of this problems now so
u can try out & find out some solution for me.

Right now i designed 128 channel data-acquisition system. During design
stage I found one problem with dg406dj. Now i need solution any how
regarding this problem. I asked my hod about this problem & he also stucked
with this kind of problem. I herewith mentioned full details of this
problem.


Right now i am using two multiplexer namely A & B. Now i fed some milivolt
to channel 1 of A & B i.e. I fed + input to channel1 of mux A. & - input
to channel1 of mux B. I select channel 1 of A & B. The output of mux is fed
to the instrumentation amplifier & then it is fed to adc & finally it
displays degree temperature. For example if i fed 20 mv between A & B, the
output which indicate the temperature shows me 120.0degree. Now when i
select channel no. 2 of A & B and i fed same milivot between A & B i.e. 20mv
between A & B. then the output which indicate the temperature shows me 120.9
degree with 20 milivolt. I thought that it might be component variation, so
i again did the same procedure but result was same. I was too surprized when
i find out the root of the problem. Now i removed Mux A & MUX B from the
circuit & select channel manually, it would be too surprized for u also
that there is not a single point one degree variation between two channel.
Now i again connect the mux a & mux b & did the same procedure, I found same
problem of variation. This is not only but two channel but between all 16
channel, the display shows me variety of reading. The maximum degree
variation between channel to channel is 1.0 degree which can not be
tolerated in my case when i claim the good accuracy & it is not feasible for
application which required accurate control of temperature. Now i explained
whole problem & i need solution very soon.

I hope u consider this problem very seriosuly & find out some possible
solution for me.

Thanking u<
Hemal Bavishi


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