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enter image description here When I connect a digital to analog converter(as shown in Figure 1) to a single-ended data-acquisition hardware I noticed that the signals are upside down. It seems like the DAC is providing differential ended output signals. Because when I connect Signal-high to + of DAQ(“a” in the figure) and GND to the – of DAQ channel(“b” in the figure) I got the mirrored(upsidedown) image of in the case of Signal-low to + of DAQ(“a” in the figure) and GND to the – of DAQ channel(“b” in the figure). But when I connect Signal-high to + of DAQ(“a” in the figure) and Signal-low to - of DAQ(“b” in the figure) there is no signal rather than some noise.

Now I’m planning to use the following differential ended DAQ hardware: http://www.mccdaq.com/PDFs/manuals/USB-1616HS-BNC.pdf Regarding Figure 2 in my drawing I’m going to connect Signal-High to “x”, and Signal-Low to “y” since it is diff-ended DAQ. This DAQ has also an Analog Common pin. Should I connect this pin to the GND of DAC.

I checked with a multimeter’s continuity mode and found out power supply’s GND which goes to DAC and DAC’s output GND are all connected. Would it be safe to connect Analog common to the the GND of DAC.

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  • \$\begingroup\$ I'm a little confused. How does your first paragraph relate to your last two paragraphs? \$\endgroup\$ – Justin Sep 24 '15 at 18:14
  • \$\begingroup\$ The first paragraph (about the first figure setup); when I dont connect the GND I get no signal. It has to be single ended. But my question is if I use a diff ended data acq. hardware how to connect the inputs. \$\endgroup\$ – user16307 Sep 24 '15 at 18:16
  • \$\begingroup\$ Question is about Figure 2 setup \$\endgroup\$ – user16307 Sep 24 '15 at 18:34
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No matter if it is a diiferential a GND must be connected. The max. input voltage on each channel is reffered to the GND. You may not leave the GND floating.

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  • \$\begingroup\$ I have some concerns about it. There are some cases they dont remmend that. I mean power supply's GND is connected all the way through the DAC to analog common in that case. Maybe something about isolted power supply thing.. So regarding Figure 2; I will connect Signal High to x, Signal Low to y and GND of DAC to analog common of DAQ. Do you think it is ok? \$\endgroup\$ – user16307 Sep 24 '15 at 19:02

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