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Subject: Switching between analog inputs

Date: 01/04/02 at 3:31 AM
Posted by: hemal
E-mail: hemal@masibus.com
Message Posted:

In Reply to: Re: Switching between analog inputs posted by Hap on 01/03/02 at 8:10 AM:

Dear Sir,
Thanks for ur nice reply. Really I stuck with this problem. I once again describe this problems in more details.
Input supply voltage to dg406 +/- 12v
Input signal is mv(not required any type of constant current source) i.e. thermocouple.
Right now i am switch ony one channel at a time & sense the ouput & so there is no question of settling time. & i din't get variation of temperature reading but what i get is the channel to channel variation even if mv of both channel are same. for example if i fed 20 mv input to channel 1 then o/p after aplification & atod converter shows me 200.2 degree. It is steady. But wheni switch next channel & fed same milivolt & switch off first channel at that time, the o/p shows me 200.9 degree. IT is also steady. there is not a single count variation. But the difference of reading between two channel is headache for me & it is not resolved by me still today.
What i observed the problem today & yesterday is I described u, so u can help me to come out from this problem.
I simply remove the mux from the circuit & connect the channel manually then this problem is no longer. but when i put mux in the cirucit & switched i/p through mux then this problem is come into picture.
I fed + input to channel 1 of mux a & switch it through mux & - input directly connected to the ground, & remove the instrumentation amplifier from the circuit then this problem is no longer but for the same specification when i put instrumentation amplifer in the circuit same problem is come.
Now what could be the reason for this problem any leakeage current??? if it is then how can i solved. Please let me know if u have any doubts regarding this explanation.

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