Function generator n00b questions.

Discussion in 'The Projects Forum' started by guestcheap, Aug 4, 2012.

  1. guestcheap

    Thread Starter New Member

    Aug 4, 2012
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    I have a function generator (3MHz sine, triangle, square ac waves, and dc). I've set it to 147.7 kHz square ac wave. Not messed with any thing else. I've clipped the black wire on to the black wire of a multimeter and done the same with the red wire. The multimeter reads 0V. Why? Also if someone could explain what the offset and amplitude dials do, it'd help.
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    A typical multimeter. Is most often made for measuring DC. And good sine wave in AC mode. Up to say around 500 Hz. Some more expensive models like Fluke true RMS meters. May handle AC measurements better. I have such a Fluke meter. But I only think it is good up to 100 KHz. In the frequency range you are using. An oscilloscope is the preferred instrument to use
    The amplitude of any wave is defined here. http://en.wikipedia.org/wiki/Amplitude
    The offset dail is used to add a constant voltage to the output. Then the offset is off. The output will probably swing symmetrical around ground level. The you offset the output. The output is moved away from this swinging symmetrical around the ground point
     
  3. guestcheap

    Thread Starter New Member

    Aug 4, 2012
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    Umm... when I change it to around 500 Hz nothing comes up either? Also, I hook up to an LED and nothing happens?
     
  4. MrChips

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    Oct 2, 2009
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    You cannot use a multimeter or an LED to test the output of a function generator.

    If you do not have an oscilloscope you can use an audio amplifier such as the speakers for a PC.

    You can also use the audio input jack on a PC and any waveform analyzer software which you can download for free off the internet.
     
  5. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    500Hz should actually show something, if your multimeter was set to AC. Was it?

    What is the model of the function generator? And what were the exact settings for the square wave? Duty cycle and DC-offset?
     
    Last edited: Aug 4, 2012
  6. t06afre

    AAC Fanatic!

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    But one thing to remember here. Is that sound cards are AC coupled. So the effect of the offset dail will be blocked. And a sound card is limited to the frequency range 20 to 20Khz. It will probably also distort a square wave somewhat. But anyway using the sound card to see what comes out from the generator is a good idea
     
  7. guestcheap

    Thread Starter New Member

    Aug 4, 2012
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    Scientific 5030-4. Multimeter was set to ac.

     
  8. WBahn

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    Mar 31, 2012
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    Have you tried repeating the prior experiment with it set to 2.5Hz?

    Are you putting a resistor in series with the LED? If not, then you probably have a dead LED.

    Can you slow it down to somethling around 1Hz or even 0.1Hz. If so, then use your meter set to DC Volts and see if you get anything. If you still don't see anything, verify that your meter is working by measuring a battery. If that checks, then you probably have a dead function generator output. Check to see if it has a fuse. Try all the various waveforms, too.

    The 20Vpp is "20V peak-to-peak". Exactly what it means depends on where it says this. It could mean that the absolute maximum output you can get it is 20Vpp (so +10V to -10V), or it could mean that you are on a range that can deliver up to that, or it could mean that you are set so that it should be putting out that.
     
  9. guestcheap

    Thread Starter New Member

    Aug 4, 2012
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    The function generator does not have dead output. I checked it with an oscilloscope today. The multimeter works. I checked it with a battery.

    What I really want to know is the voltage output of the function generator. Any way to find that?
     
  10. MrChips

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    Not with a multimeter. Use the scope.
     
  11. praondevou

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    If you checked it with an oscilloscope then you should know the output voltage, right?
     
  12. guestcheap

    Thread Starter New Member

    Aug 4, 2012
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    Nope. Had it tested by a friend. Personally, I don't own a scope. If you connect the clips to a coil of wire, will it still be an ac wave of the same frequency?
     
  13. MrChips

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    Well, get your friend to come over again and measure it with a scope.
    He should be able to tell you the amplitude, frequency, DC offset and shape.
    That's what scopes do.
     
  14. WBahn

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    If you checked it with an oscilloscope, why didn't you measure the voltage output then?

    EDIT: Didn't see the second page and that this had all been brought up.

    Have you tried any of my recommendations, such as slowing down the output to <1Hz?

    Are you sure there isn't an attentuator that is engaged?
     
  15. praondevou

    AAC Fanatic!

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    Yes the load will not change the generator's output frequency. It will / can change the waveform and phase though.

    As mentioned, if you adjust the frequency to 1Hz or less you can measure the voltage with the multimeter adjusted to DC.
     
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