Adjusting a broken function generator

Discussion in 'General Electronics Chat' started by afaik, Dec 22, 2008.

  1. afaik

    Thread Starter Member

    Nov 2, 2008
    In school, I had the misfortune of working with a function generator that would output a wrong frequency. Another student showed me a way how to adjust it by setting the oscilloscope and observing the waveform generated on the screen. Unfortunately I'm probably not going to come across this student again. If anyone is familiar with this, I would greatly appreciate you sharing this handy bit of information. Thank you.
  2. leftyretro

    Active Member

    Nov 25, 2008
    Pretty straight forward, as long as your scope has a calibrated time base and it sounds like yours does. Have a signal attached to the vertical channel, it's amplitude doesn't matter as long as it's strong enough for your scope to sync to and show a steady display. Counting the graduations on the horizontal scale of the scope count the number of major minor and ticks that one complete cycle (two zero crossings) of the signal takes. Multiply that by the time base position on your scope's horizontal time base knob.

    You now know the time for one wave length of the frequency. Now divide that number into one (get the reciprocal) and you will have the frequency in hertz per second. You can of course adjust the frequency of your generator after first determining how many division of horizontal space that frequency should occupy.

    I'm sure there are instructions on the web if my explanation is too cryptic ;)

  3. afaik

    Thread Starter Member

    Nov 2, 2008
    leftyretro, I've got it down, thanks alot. I had to simplify it so I can remember it in the future, but this is what I got.

    Boxes Horizontal of one wave form times Time Division = Frequency. Reciprocal of F = Hertz

    BH * TD = F. 1/F = Hz

    And if you know what frequency you want, but just need to output it,
    1/Hz = Frequency.
    F/TD = Boxes Horizontal.
    Set your scope to your chosen time/div and adjust the waveform until it appears as so many boxes horizontally as the calculations state.
    Thanks for your help!
    Last edited: Dec 23, 2008