voltage-to-current converter chip for oscilloscope XY mode for curve tracing?

Discussion in 'General Electronics Chat' started by relicmarks, Apr 6, 2008.

  1. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    voltage-to-current converter chip for oscilloscope XY mode for curve tracing?

    Using a oscilloscope in XY mode is voltage verically and voltage horzontally

    My goal is to use the oscilloscope to do curve tracing or component characterists like what a signature analysis test gear does

    If i put my oscilloscope in XY mode and try to measure a resistor it doesn't Curve trace, if i try to measure a capacitor it doesn't curve trace either

    Do you have to hook up a AC generator to the resistor or capacitor when doing curve tracing on the oscilloscope?or use a power supply hookup up to the component being curved trace?

    So channel #1 on the oscilloscope is set to the vertical display for voltage
    Channel#2 on the oscillscope is set to horizontial display for voltage

    If i use a voltage to current converter chip on channel#2 will the oscilloscope be able to do V/I curve tracing? (i would need a current oscilloscope probe too)
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    An Octopus is a cheap & easy way to get you going.
    http://octopus.freeyellow.com/octopus.html

    It's limited though, because you only have 60hz to play with.

    If you want to plot out transistor response curves, you're going to need to build some hardware a bit more sophisticated than an Octopus.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    You don't get any display because curve tracers are active devices. Resistors don't generate curves, either. You check them with an ohmmeter.

    Here is a link to a V/I curve tracer that is closely related to the octopus, but a bit more flexible - http://www.techlib.com/electronics/curvetrace.html.

    Google comes up with 200,000 hits on "curve tracer". You can get a lot of good information about how they operate from the articles.
     
  4. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    So there is no way at all to make my oscilloscope do curve tracing?

    Why is curve tracing active?

    Do you guys know where there is any charts and graphs about component signatures or the components being curved trace , i just need the typical signatures
     
  5. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    On Y you need the measuring voltage. On X you need a ramp voltage.
    Every other signal than voltage must be converted to voltage (ie using a simple zero drop current to voltage converter with OA).

    For a curve tracing you need a variable voltage (ramp) applied on X input and through a voltage to current converter applied to DUT (device under test). The DUT response (which is a voltage) will be applied on Y input. That's all.
    Can you please give me a block diagram how i should hook this up please?


    Block diagram:


    1.) Power supply set at 5 volts goes to one side of the resistor or capacitor ( DUT)
    2.) oscilloscope Y channel goes to one side of the resistor where the 5 volts is at
    3.) Set a function generator for a RAMP voltage goes to the other side of the resistor (DUT) or capacitor ( DUT)
    4.) Oscilloscope X channel goes to the other side of the resistor or capacitor
    5.) Put the voltage to current convertor IC chip inbetween the Oscilloscope X channel and the (DUT)?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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  7. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    Yes i have a generator with a RAMP mode

    But how do i hook it up to a (DUT) componont with a voltage to current IC chip with the oscilloscope to do Curve tracing please?
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    An oscilloscope can't directly trace current.
    Current must be changed to a voltage by using a resistor, or device with impedance.
    The deflection of the electron beam in the tube of the O'scope occurs due to variations of the voltage on the intput channels. You can determine the current in the circuit by using Ohm's Law with your known values (voltage observed vs known resistance/impedance)

    Why don't you start off by building the most simple of one of the devices that has already been linked to, follow the instructions already provided on those pages, and compare the results you get to the results they received?

    Take a look at this page:
    http://greynet.net/~gbarc/feedback/may75.htm
    Scroll about 3/4 of the way down the page for a very basic circuit:
    [​IMG]

    And further down, you'll see the kind of output to expect (idealized waveforms):
    [​IMG]

    Note that if you have combinations of components connected, you'll get a result reflecting that, such as:
    [​IMG]

    I highly encourage you to build the basic circuit, and experiment with it.
    Note that many cheap transformers saturate easily, which will distort the output waveforms. You can get around this by using two of these cheap transformers, wiring the primaries in series. Example: get two 120v-12.6v transformers that have no center tap, and wire the primaries in series. Now the primaries get 60v each dropped across them, and the secondaries have a 6.3v potential across them.
     
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