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differencial output

 Please help (LabView beginner), could the differencial pair output directly wire to a graph? I would assume it should wire to a diff. amp. before goes to the graph.
However, I can't find diff. amp. or OP amp. on function palette, any hint please.....Thanks!
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Message 1 of 11
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are you a having 2 sets of values whose result you that you want to display on a graph after passing it through a software equivalent of an op amp??

plz eloberate

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Message 2 of 11
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You should be able to directly wire as many signal as you want to a waveform graph/chart. The only thing that you need to keep in mind is that you need to expand the plot legend to show the number of plots you have wired. When you do this you can have multiple inputs on the same graph/chart. You can also give them different scales if you want to as well. Let me know if I can do anything else for you. 🙂
 
Tyler H.
National Instruments
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Message 3 of 11
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THanks for the hint. My problem is not multiple channels display, let's nail down to one pair of diff. signals. Say A+, A- coming from USB6009 probe.
If I wired both to the graph with one name "SumA", the graph shows canceled signals (GND + noise). I assume the graph simply add both up?
If this is a piece of hardware, I would wire both signals to a diff. amp. with gain = 1, then I should see SumA, right? But I am not able to find diff. amp.
in the pallete. Thanks for your time.
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Message 4 of 11
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 My problem is not sure if the graph will automatically sum a pair of diff. signals or do I need to provide a diff. amp. with gain = 1, then wire to the graph.
If I do need wire to an amp. then where are them on the function pallete?
Thanks!
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Message 5 of 11
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Let's separate hardware from software. The USB 6008 supports differential measurements so you should configure the hardware for that and connect your signals to the correct pins. It's probably AI0 and AI5 but I haven't used the 6009 so you should check your manual to see if that is correct. You configure the hardware in one of a couple of different ways. You can create a channel in MAX and configure it there. You can use the DAQ Assistant and configure it with that. You can also use the DAQmx Create Channel and specify "Differential" for the input terminal configuration. If you do one of these, then the DAQmx Read will return a single voltage reading that you can wire to the graph.
 
If you want to do it all in software, then setup two channels for single ended measurements and when DAQmx Read returns both values, use the subtract function (Numeric palette) to get the single differential voltage that you wire to the graph. The graph does not do any adding or subtracting. It simply plots the channels you acquire data from. If you wire the results of a 2 channel scan, you get two separate plots.
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Message 6 of 11
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Thanks very much Dennis. I believe 6008 and 6009 are diff. on sample rate (10K vs. 48K); wiring is the same. I am using DAQ assistant method and
measuring 10/100 diff. pair. AI0 to AI3 are config. to diff. input. But I don't see the diff. signals add up on the graph, instead they cancel each other. I will
try basic such as measuring Vcc, GND, -voltage to verify this. Also, I will try to set "invert" box to the negative signal, that might be where I screwed, the
software may treat AI0, AI1 the same, even the hardware named AI1 as inverted signal.
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Message 7 of 11
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Signals do not get added up or canceled in a graph. I also don't know what you are talking about when you mention an "invert" box. The DAQ assistant has no "invert" box - at least not with analog acquisition. If you have a +3V signal at AI+ and a +1V signal a AI-, then DAQmx Read will return a +2V measurment for this channel. If you have another channel with exactly the same levels, DAQmx Read will return the same measurement and the graph will overlay one signal on top of the other in the display but they are separate and no math is performed between the two.
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Message 8 of 11
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Hello OPamp,

To add to what Dennis said, the specifics for the USB-6009 are a measurement for AI0 will be the potential difference between terminal 2 and terminal 3.  And the measurement for AI3 will be the potential difference between terminals 11 and 12.

Regards,
Micaela N
National Instruments
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Message 9 of 11
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Thanks very much, I understand now. The target (10/100) was bad, I didn't have signals. With a good target, I see it now. Thanks!
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