# vkristof

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1. ## Question on FFT of DC value

Background: I've been using the AD2/Waveforms to measure/analyze low-level/low frequency signals that have a DC component that we care about. The signal is in the feedback loop of a system, and the AC & DC components are in ~ 1mV range. We have a 200 Hz LPF with a gain of 10 (offset trimmed) before we feed into the AD2 (and a Keysight Benchtop DMM & a Tek TDS3034C). The attached .png shows the standard "Measurements" of the 1V DC as a reference. My question is related in conceptualizing the FFT of a DC signal, and specifically, why do the O Hz and and next bin up read 3.01x and 2.70x dBv (in other words greater than 0 dBv) when I feed 1 V DC into CH1. Any attempt to educate me in understanding this seeming discrepancy is appreciated. Please note that I checked the FFT portion with sinusoids from the AWG previous to this DC check, and the FFT bin contents (dbV values, whatever) were what I expected. In this specific case the AWG is the source of the 1 VDC and the AD2 Scope/measurement reading are 1V (along with the Tek & Keysight readings). Copy and paste from the excel of the FFT below. Bins go out to 4K, scope sample rate is 8k (as expected) #Digilent WaveForms Scope FFT #Device Name: Discovery2 #Serial Number: SN:210321B21C1B #Date Time: 2021-08-25 17:12:26.733 NOTE: this FFT is available in it's scope capture form as .csv/.xlsx and .png. FFT is of a +1.0 V DC from the AD2 AWG and AD2 Measurements reports 1.000V DC RMS, 1.0008 V Average, etc. Frequency (Hz)Channel 1 (dBV)Phase (deg) 0 3.017895119 0 0.488281 2.708513213 0.010973 0.976563 -0.79016818 0.022399 1.464844 -11.22347699 0.034118
2. ## Verification of details of AD2 scope measurements pane: Value & Average

I'm using the AD2 scope (with Waveformsrunning on W10) to measure low frequency signals (example Timebase 100ms/div) and am specifically interested in the AC RMS and DC RMS calculations AND Average Column and how they interact with the Single and Run buttons I'm assuming the Value calculations are run once (& displayed) once the scope buffer (8k or 16k) is filled, is that correct? I'm also further assuming that the Average column is then a running average (assuming the "Run" button is clicked) of the Values column as the scope buffer is filled, Value is calculated, etc. So, for example, if the scope Run had filled the buffer twice, the Average column would just be the average of the two sets of values that had been calculated, is that correct? Thank you.
3. ## Welcome!

Hello all, I'm an old HW eng with an AD2 connected to a W10 laptop. I've been primarily using it for the scope/measurements function to measure low level & low frequency signals. I'll probably be posting questions related to how, exactly (buffering, etc.), the RMS values are calculated in the Measurements page. I've also used the Network analyzer (and the Power Supply function), which is pretty straightforward.
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