04-26-2018 06:20 PM
Before I talked about the problem, Let me briefly introduce the background. Basically, I applied a voltage across a membrane with a pore and measured the current passing through the pore (Resistive pulse sensing). Usually the current should be a flat current with a noise band around 200 to 300 pA if voltage is controlled by other DC power supplies (I tried two different ones and named them as 1 and 2)
Since I have to control it in real-time. So I used a DAQ board(PCIe 6321) and BNC board (BNC 2110) for DC analog output.
The problem is: when I used BNC board to generate DC analog output, the current measured is much more noisy (>1000pA, see attached pic 1 for comparison).
Then I compared the three DC output voltages (9 volt). I found out that there are lots of spikes in the output (See attached pic 2). However, when I plot all of them and did a spectrum analysis. It shocked me that the DC output from BNC board actually has a much better precision, and the smallest fluctuation and high-frequency component (see attached pic 3).
Does anyone know why? Greatly appreciated! (I am new in DAQ)
04-27-2018 09:09 AM - edited 04-27-2018 09:09 AM
Sounds like a question for a good Electrical Engineer, equipped with oscilloscope and knowledgable about impedance matching, proper grounding, and shielding.
Bob Schor
04-27-2018 09:14 AM
Thanks for the reply. But a good electric engineer is always hard to find.
04-27-2018 09:31 AM
Well, if you have access to a library, you can probably find some textbooks. Check the hobbyist Web sites. Do a search for "Grounding and Shielding". Look up "Impedance Matching".
Bob Schor