help with oscope - using trigger delay and sweep delay

Discussion in 'General Electronics Chat' started by kcroy, Feb 22, 2014.

  1. kcroy

    Thread Starter New Member

    Dec 24, 2011

    I'm new to using an oscilloscope and am working on getting a steady image of a wave form to observe.

    I am hoping someone can provide feedback on my "technique", and help answer a few questions. I don't come from a science/engineering background, so some basic concepts might take me a while to grasp. any help appreciated!!!

    I am using a tek 485 scope. My source is an audio file of a square wave form played on my laptop - the sound plays for 3 seconds, and then loops with a slight pause in between loops.

    1) Here I start by using the horizontal fine tuning adjustment. I don't understand why this slows down the left/right scrolling of the wave.

    2) This is what I think is the right technique ( from what I have read ) . I adjust the trigger voltage level to stop the scrolling. Then to remove the offset duplicate, I adjust the trigger delay.

    Why is a trigger delay necessary in this case?

    3) Once I have a wave, how do I adjust the corners so it is more "Square" around the edges... I could have sworn the guy I bought this from showed me a way to adjust this. I understand it shouldn't be perfectly square, but shouldn't it look more like the red lines I have drawn below?


    Thanks in Advance!
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    1) Don't touch that knob. It does not do what you think it does. It only seems to work because you don't have the signal triggered by the scope. Once triggered the signal will stay in place.

    What you are doing with that knob is changing the time for a left to right sweep, and at certain points you've got an even multiple between sweep speed and signal period, so you see a repeating pattern. But that is not recommended (as you now have no time calibration).

    I can't think of reason offhand to use that knob in between the 1:1 and 10:1 settings.

    2) The resolution of the movie is too crude to have any idea what the scope settings are: there are several knobs and switched that interact to get a good trigger. From the looks of the trigger level knob you're triggering on some very low piece, such as the little bit of negative overshoot, instead of the very distinct middle section.

    There is no need to adjust trigger delay to anything beyond zero to see this wave.

    3) That adjustment is for the scope probe, not the wave you are looking at. Tektronics scopes (and every other one I've seen) have a CAL output on the front panel. Touch (or clip) the probe to that, and on the back side of the probe BNC connector is a small opening: adjust the screw inside till you get the best square edge you can.

    That "calibrates" the probe, and the book says do it at the beginning of every measurement session.

    (Practicably, people only remember to do it every year or so, about an hour or two after no luck figuring out the distortion on their signal.)
  3. bance


    Aug 11, 2012
    Alan w2aew did a good series of videos on basic scope use:-

    This one covers triggering controls!

    HTH Steve.
  4. kcroy

    Thread Starter New Member

    Dec 24, 2011
    Excellent thanks!

    Would you mind taking a look at this updated video to see if my technique is correct? Set the voltage until I can see it on scope, then adjust the horizontal time until I see a decent waveform. Part of what confuses me here - I am using an audio sine wave, and I get duplicates of the waveform until I adjust the trigger level.

    Shouldn't this be stable waveform with a trigger voltage of 0?

    Thank you, I had misremembered what he was showing me! I found a helpful video of the process for anyone who comes across this thread:

    Thanks again for all the help!