Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Voltage adder

kyle,

If there is anyway to float the source of the signal, things
are simpler. Sometimes you can float a signal by using a 3 to 2 plong
adapter on the power cord of the signal source. Then you can just
connect the signal source's internal common to the compeuters, ADC common
by way of a couple of batteries. This works equally well if the ADC's
ground is floating, or if it has differential inputs.


-------------------->>-------->>------
+2 to -2 V
Signal | ADC
-------------------->>--| |--->>------
signal common |
batteries

If the signal and the ADC commons are tied to earth ground
then you probably need either an isolation amplifier or an OP AMP
set as a signal adder. One can look this up in some of the Radio Shack
electronics notebooks. If you need to make absolute measurements or
your frequency is very high, you need to use good components.

If your frequency is in a reasonable range ( whatever that
might mean here) you might try a small 1-1 isolation transformer. again
if the frequency range is large and it gets you into LRC resonance, or
just where the inductive impedance becomes a problem this will fail
to give good results.

Thanks

roger haar
physics U of AZ


**********************************************************************
On Tue, 17 Dec 1996, kyle forinash wrote:

I've got a +2 to -2 volt AC signal and an A/D board that reads 0-5V. Can
anyone with more electonic experience than I tell me the best way to add
2.5V DC to the signal so that it is centered in the A/D board range? I seem
to recall there is a standard way to do this but don't see it right off in
the books available to me right now.

Thanks,
kyle

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
! kyle forinash 812-941-2390 !
! forinas@indiana.edu !
! Natural Science Division !
! Indiana University Southeast !
! New Albany, IN 47150 !
! http://Physics.ius.indiana.edu/Physics.html !
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!