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So I've been playing with doing SGM with a D5000 and a NS V controller. I just want to send the DC analog voltage from my external lock-in into the Nanoscope for collection as a data channel. When viewed on the Lock-in display panel and via an old oscilloscope, my lock-in output is a nice DC voltage with 2.5 V fs. When it gets to the NS as a data channel, however, the signal appear sinusoidal, with an amplitude of about 10% of the DC voltage - so I'm getting a signal with rms of 1.15 V but an amplitude of >100 mV, which is not cool. I thought it might be because Input 1 has a low input impedance, but sticking a 1 M-ohm resistor before it didn't help matter much. What is everyone's favorite way to read in a data channel? Could the sinusoidal nature be due to the sampling rate? Advice, thoughts?
I took a good look at my oscillation - it's 60 Hz noise. How are the front panel inputs on the NS V controller grounded?
That level of noise is way too high. From what you describe it sound like you have a ground loop problem. These can sometimes be tricky to isolate, but often can be found with just good grounding practice.
In general try to get all of your grounds to a single point. This can be done by plugging all of your equipment in at the same point. Or by using “two prong” adapters, and grounding your equipment through the BNCs shield. Also make sure *all* of your equipment and instrumentation ground’s are connected.
You can often troubleshoot a ground-loop by making a “ground probe” (a wire clipped to the NSV ground) and look for changes the 60Hz signal as you touch the different elements of your system.
If you try all these basic steps and you still have a problem, please post a detailed schematic of your system (including grounds) – or contact me offline.
Regarding adding a resistor in series with the input: this will likely hurt your performance, as you are creating a voltage divider with the input impedance of the NSV. In general, you want Rout low and Rin high. The “measured” signal is attenuated by Rin/(Rin+Rout), where any series impedance increases Rout.
Good luck!
Steve