Oscilloscope question

Discussion in 'General Electronics Chat' started by PRS, Dec 30, 2009.

  1. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
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    I have a Tektronix 475. Both vertical amplifiers are scaled by 1-2-5 and go up to 50 volts per division. And yet both stop at 5 volts per division. Is there a trick to turning these knobs higher?

    If only one were stuck at a maximum of 5v/div then I'd say a switch was malfunctioning. But both do the same and so it seems to be intentional. Any ideas on how I can get to the higher scales?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Usually these scopes are used with 10X probes which would equate to 50 volts per vertical division.

    hgmjr
     
  3. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
    989
    35
    Yes, but why the scale on the knobs showing 50 v/div max. if it can't be used?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    The 10X probes have spring pins that contact a metal ring around the BNC connector. That contact causes the indicator illumination to switch from the 1X to the 10X markings.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If your probes are 1x/10x, try switching to the 1x position.

    However, your readings will be more accurate on the 10x position.
     
  6. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
    989
    35
    So there is a special 10x probe? Not the kind that switches from 1x to 10x, but a special dedicated 10x probe?
     
  7. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
    989
    35
    Didn't work. But thanks. At least I can use the probes I have on 10x to read the higher voltages. I hadn't thought of it. (This was the first time I tried to read a voltage higher than 30 volts peak to peak, using this scope.)
     
  8. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    I had the same question just a few days ago. Apparently these divisions are for special high voltage probes. These probes have a special collar on the VDC connector that activates the second voltage division light.


    If you will look, the 2nd division light goes all the way up 10 100V per division.
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    As stated in earlier posts, the dials are "double scaled" to show you the volts/division depending upon a 1X or 10X probe. It is ASSUMED (yes, we know what that does) that the user will know what kind of probe he is using. The double scale eleminates the need to do the mental calculation of adding a zero if using the X10 probe. Some scopes, when using a probe designed for that scope, WILL switch the lighting from one side to the other. If you look closely at the BNC connector, see if it has an obviously insulated ring that would appear to be on the same plane as the front pane. If so, ground it to the main shell of the BNC connector. The light should switch to the higher calibration.
     
  10. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
    989
    35
    Thank you very much. You've all been a true help. I don't have any special probes so I'll take up Sgt Wookie's idea and use regular probes on the 10x position.
     
  11. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
    989
    35
    Thanks. I think you're right. But my scale goes up to a max of 50 volts per division with 8 divisions for a maximum of 400 volts.
     
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