Help with Winscope/Voltage things

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

1. PantherGuest

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

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. RichardGuest

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 MastaGuest

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

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 GriseGuest

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

Have Fun!
Rich

5. PantherGuest

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. PantherGuest

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. PantherGuest

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 BettsGuest

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

Bye.
Jasen

9. Rich GriseGuest

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 jayGuest

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 jayGuest

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. ehsjrGuest

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. PantherGuest

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

14. PantherGuest

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

Thanks

15. PantherGuest

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

Thanks

16. operator jayGuest

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