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Help with Winscope/Voltage things

Discussion in 'Electronic Basics' started by Panther, Dec 21, 2005.

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  1. Panther

    Panther Guest

    Hello everyone

    You may remember me from before well I've done the practical now and I've
    some results. I decided to use a capacitor resistor network and connect it
    up to a computer with WINSCOPE (please download, it's really tiny size and
    doesn't affect your computer: http://polly.phys.msu.su/~zeld/oscill.html).

    I have a few queries. It shows a graph of voltage vs time. The x-axis
    represents time, and I know that. What I'm trying to do is this: I have some
    screen grabs of voltage discharge/charge curves, and I'm trying to find the
    voltage after 5 time constants (I know where). But I need to read off the
    voltage at that point, how do I do that? Does something called "Y1 Gain"
    make any sense? I've no idea how to convert that nonsense into voltage.

    Should I just use percentages or something? Thanks.
     
  2. Richard

    Richard Guest

    Since you know the x-axis represents time and the graph is "voltage vs
    time", then the y-axis is-----ta dah---voltage.
    I am not familiar with Winscope, but if you have graticules on the screen
    (lines depicting divisions of the x- and y- axes) and you know the settings
    of your time and voltage controls, you can compute the time and voltage over
    any given distance. Most scopes have a control for the y-axis that is
    labeled volts/division. If this were set to 1, each y-axis division would
    indicate 1 volt of amplitude. Works the same for time on the x-axis. Use the
    major divisions - sometimes these have minor divisions, usually 5 per
    graticule, to help you interpolate if the waveform edge doesn't fall exactly
    on a major line.

    There is also the issue of the baseline to consider. Zero volts may not be
    where you think it is.

    Try Googling for some basic information on oscilloscope operation so you can
    learn what all the usual controls do, then read the documentation that came
    with Winscope(?) to see what any unusual controls do.

    Hope this helps.

    Richard
     
  3. Bob Masta

    Bob Masta Guest

    Hmm, I'm not sure exactly what you are doing, but I'd
    just like to point out that since this system uses a sound
    card for input, it is AC coupled. That means that any
    time constants you are trying to measure will have to
    be much shorter than the time constant of the input
    itself. The input is usually a few Hertz high-pass, but
    could be up to 20 Hz or more on older/cheaper cards.
    So this system probably won't be of much use in
    trying to meaure time constants longer than
    50-100 msec.

    As far as getting absolute voltage readings, there
    is absolutely no way to do this via software. The Windoze
    driver doesn't consider this sort of thing in the least,
    and there is no place in it for calibration values to be
    returned to the program. You will thus have to do the
    calibration manually.

    First, be sure you have the Windows Mixer sliders in
    a known configuration. Given the crudeness of the
    Windows Mixer, that pretty much means maximum
    volume. Then apply an input signal of known
    amplitude and read it on the trace. Use that as
    the basis for your calibration. Of course, you must
    keep the same mixer settings on all future uses.

    My Daqarta for Windows software will adress all
    of these issues, but it won't be released for a couple
    of months yet. I'll post a note here when it's ready.

    Best regards,



    Bob Masta
    dqatechATdaqartaDOTcom

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Home of DaqGen, the FREEWARE signal generator
     
  4. Rich Grise

    Rich Grise Guest

    Just do the arithmetic. Since this is crossposted to basics, I'm going to
    go ahead and look up the formula for you, just because I'm such an
    insufferable sweetheart. :) You do remember that T = RC, right? Well,
    the voltage at 5T ...<Rich googles>

    http://www.albany.edu/faculty/jae/quarknet/html/rc_circuit.html
    http://www.antonine-education.co.uk..._1/Topic_10/topic_10__rc_networks_with_dc.htm
    http://www.oz.net/~coilgun/theory/capacitorcharging.htm

    are the first three hits on

    http://www.google.com/search?q=exponential+decay+capacitor

    Have Fun!
    Rich
     
  5. Panther

    Panther Guest

    Thanks but I've done that already (as in I know 5TCs will give me the
    voltage) what I meant was I dont know how to read it off the graph Winscope
    gives me.
     
  6. Panther

    Panther Guest

    Unforunately Winscope doesn't have any divisions (that I've seen) which tell
    me anything about the voltage. Its documentation is poor too.

    Thanks anyway.
     
  7. Panther

    Panther Guest

    No that is impossible because I've done the practical and now I've to do the
    write up so there's no chance of me doing it again :(
     
  8. Jasen Betts

    Jasen Betts Guest

    ["Followup-To:" header set to sci.electronics.basics.]
    Time constant is resistance times capacitance
    Time in seconds, resistance in ohms, capacitance in farads.
    AIUI that will scale the output reading.

    if at some point the voltage was at a known level all other results will be
    proportionate to that reading.

    Bye.
    Jasen
     
  9. Rich Grise

    Rich Grise Guest

    So, if the graph is important, then do the arithmetic on your pocket
    calculator, and draw the graph on a piece of paper.

    Good Luck!
    Rich
     
  10. operator jay

    operator jay Guest

    If you told us about the lab we might be able to figure out your final
    voltage, then you can scale V @ 5TC. Or, hand in your assignment in p.u.

    j
     
  11. operator jay

    operator jay Guest

    The help file you downloaded with the software says the maximum input is
    about 2VAC. You could assume that your volume control sliders were set all
    the way up, and then assume that the maximum levels are +-2.5V or +-3V (or
    something in there) and then factor in your gain (probably Y1), and hope
    that that gives you a correct scale. Not as bad an idea as it sounds. Make
    your assumptions and write them in your lab report, right up front. Give
    your answers in volts and in p.u. of the maximum voltage you saw.

    j
     
  12. ehsjr

    ehsjr Guest

    The write up at the link you posted says there is a
    point and click meter function. Can you use that to
    find the voltage?

    Ed
     
  13. Panther

    Panther Guest

    Yeah I will proabbly do that if nothing else works. THanks
     
  14. Panther

    Panther Guest

    OK so the bottom-most point is -3V and the top is +3 (or 2). I can
    understand this but what does the Y1 gain have to do with it? How will it
    affect what I read off?

    Thanks
     
  15. Panther

    Panther Guest

    OK so the bottom-most point is -3V and the top is +3 (or 2). I can
    understand this but what does the Y1 gain have to do with it? How will it
    affect what I read off?

    Thanks
     
  16. operator jay

    operator jay Guest

    You probably divide by Y1 (or Y2 if your signal was in input 2 and shown as
    trace 2).

    j
     
  17. Guest

    is it? depends on your position and gain settings, plus various other
    factors outside the winscope program.
    Its exactly the same as input gain on any old hardware scope. It sets
    the gain applied to the imcoming signal, just like a volume control.

    If youre not understanding how to use winscope, then I think youre not
    understanding how to use oscilloscopes full stop. OSC251 is as simple
    as it gets.


    NT
     
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