Help with first pc scope please

Discussion in 'General Electronics Chat' started by s_mack, Oct 6, 2012.

  1. s_mack

    Thread Starter Member

    Dec 17, 2011
    187
    5
    So I got a QA100 digital oscilloscope/LA combo. It appears to work... I just don't think I know how to use it. The instructions appeared OK, but maybe its less to do with *this* scope and just more about scopes in general... but I'm getting nowhere fast.

    It has a test point that's always outputing a 1 khz 1v sine wave. When I connect the probe to that, I indeed see the wave as expected. That's how the instructions say to confirm its all working fine. But then I can't see ANYTHING else. As a simple (I thought) example, I plugged in a USB connector with accessible +5v and GND leads. I expected that if I touched the probe to the +5v that I'd see a line on the screen representing that. But I get nothing. The software has a DVM setting so I tried that, and it doesn't react at all when I touch +5v. I touch the 1v reference again and it responds. I test my +5v with a regular DVM and it shows 4.91v. I tried the 2nd probe... still no luck.

    What am I doing wrong?

    I don't know that it matters, but I had a little trouble with calibration. It asks me to use an external DVM to read the true RMS voltage on that reference pin and I got something like 1.2 but it wouldn't let me enter that because it only accepts a value between 0.85 and 1.15. It also says you can leave it at 1.000 and it should still be fairly accurate so that's what I did. Now when I use the built-in DVM function on that reference it shows 1.59v RMS so I'm a little confused on that as well.

    I have contacted their customer service but I thought I might get quicker help here as they are pretty slow to respond on their forum.

    Thanks.

    - Steven
     
    Last edited: Oct 6, 2012
  2. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    if I am following you right, the 1v/Khz reads ok.........to measure the other, you will need to set the scope for DC measure............. for +5v At that rate, the trace will jump from your zero line, up to whateever on the scale is representing 5v, tho' it will be a straight line vs. a sine wave.
     
  3. s_mack

    Thread Starter Member

    Dec 17, 2011
    187
    5
    Yeah, I got my wires crossed (figuratively) :)

    First, I was mis-reading the intention of that 1v/Khz pin and was using that for calibration when I'm supposed to be using the AWG. So I've got it calibrated OK now. Second, I had the channels mixed up when trying to scope the 5v. I had CH2 set to DC but I was using the Ch1 probe (duh).

    I think I'm in business now. Thanks for your response.

    - Steven
     
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