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The Origins of Delayed Timings on Oscilloscopes - Workbench Wednesdays 43

 

Almost everyone uses a digital oscilloscope’s zoom features. However, did you know that 40-year-old analog oscilloscopes can do something similar? Delayed time bases on analog scopes sweep twice so that the user can see a slow and fast sweep. In this video, see where “zoom” came from and how engineers accomplished the same measurement back in the day.

 

Minor correction about the old scope that I showed. I kept calling it a “7704.” The 7704 is from the early 1970s. The unit I have is actually the updated model the 7704A.

 

Supplemental Content: 

  

Bill of Material:

 

Product Name Manufacturer Quantity Buy Now
Bench Oscilloscope - 200 MHz, 1 GSa/s, 14-bit, AFG, DMM Multicomp Pro 1 Buy Now
Arbitrary Waveform Generator - 2 Channel, 160 MHz Multicomp Pro 1 Buy Now

 

  • in reply to kmikemoo

    Right? While making this episode, it occurred to me why so many people struggle to use oscilloscopes (analog or digital.)

     

    Modern digital oscilloscopes are made about as easy-to-use as they can be. But, their enormous flexibility can make them a nightmare for the new user. Add to that, when starting with a scope, most people don't know what should show up on the screen. So they don't know if they are seeing a problem in their circuit or they just don't know how to set up the scope.  I realized this point, in reverse, when setting up the analog scope.

     

    Hmm.

  • Great episode.  It's amazing how powerful even the old technology was - you just had to figure out how to use it. image

  • Great episode.

    I spent a lot of time using those features and would loved to have had a 7700 series Tektronix scope, but had to make do with older models.

     

    The 1970's was an interesting time where circuits and signals were achieving speeds that challenged the available test gear.

     

    Learning tricks on how to squeeze more performance from older test equipment became the mark of a good engineer.

     

    DAB

  • What an awesome episode and comparison. I find old scopes fascinating. 

  • Question from YouTube:

    Is delayed timebase the same as hold-off?

    The short answer is no. "Delayed Timebase" is a means of having two timebases on the screen at the same time, where one of the time bases is delayed by the other.
    Trigger hold-off is a timer built into the trigger circuit which determines how long until the trigger can re-arm itself. In both analog and digital oscilloscopes, after a trigger event is detected there is some amount of time before the trigger can detect another event. In analog scopes, the time is generally limited to how long until the sweep can trace across (and back) to the start of the screen. In digital oscilloscopes, the minimum re-arm time is a function of how long it takes to fill the acquisition memory, empty the buffer, process the samples, drawn them on screen, do measurements, etc before the next acquisition hardware is ready to capture samples again.

     

    Hold-off adds time to that minimum re-arm time.

     

    Typically, you'll want it to be as small as possible. (As of today, no scope has "zero" re-arm time.) But there is at least one case where it can be helpful to increase the re-arm time.
    If you have a digital pulse train that is relatively long, it is possible for some scopes to trigger somewhere in the middle of the pulses between acquisitions. This behavior results in an erratic display. BUT, if you had a relatively long inactive time before the train started, you could tell the scope to wait at least that long to re-arm itself. It'll take a few acquisitions, but eventually, you'll only be triggering at the start of the train.

     

    (Note that in general, a greater-than pulse-width trigger is a better choice in that case. But not all scopes have that.)

     

    Another case is if a random glitch occurs, you can effectively ignore it by making sure the re-arm time is longer than the glitch.