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This question is a bit related to an earlier question: Question

With my current scope (Philips PM 3253, 20 MHz 2 channels), I cannot measure the quality of edges from square waves from the test signal, because if I put the time to less than 1 ms, I either don't see anything or a straight line.

I assume this is a problem of the scope (it has a quite bad screen, the beam stays 'forever' or is fading away fastly, so all the time I have to press the 'reset 'beam'' button.

Is there something I do wrong? I already know I should use the 10:1 setting on the proble, but still have the same problems.

So I'm in the market for a new (old analog secondhand oscilloscope) and was wondering how to best do a test similar to this?

My idea: use a square wave (which I guess never is 100% square). I put the time to e.g. 10 us or whatever and I would see square waves which connect the 0 and 5V (or + or - volts) together with a 'rather' steep line. And I want to measure the time from 0 to 5V or vice versa. This should be something in us I assume.

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    \$\begingroup\$ Most scopes have a test output for calibrating a 10:1 probe. Usually this is a 1 kHz, 1 V or 5 V square wave. First step is to get that square wave properly displayed with 3 periods or so. When you have that, set the timebase to smaller values to zoom in horizontally. You might need to adjust the trigger level to see the slope on screen. Take small steps and adjust until you see what you want to see only then adjust again. If you take too large steps, like going to 10us immediately you will "loose" the trace. With more experience, you will do that in one go but not yet. \$\endgroup\$
    – Bimpelrekkie
    Jul 5, 2017 at 13:15
  • \$\begingroup\$ So maybe my scope is working correctly? (except for the fading or forever visible lines) ... I hope I have time in the weekend to try this. I have indeed a test signal but it is not specifically for 10:1 probe. I can also 'delay' the measurement but that never gave me any good result. And I can 'store & hold' but also that does not show any good result. Maybe I should make a video to make it more clear. \$\endgroup\$
    – Michel Keijzers
    Jul 5, 2017 at 13:51
  • \$\begingroup\$ I think what you should do is let the "delay" (delayed timebase) at 0 (zero) for the moment and just try to get a decent graph. Sounds to me that you need to learn a bit more how to operate a scope. There are videos and tutorials for that. Almost all scopes (especially analog ones) operate in a similar way. So it does not matter what scope is used. Just "trying" a setting to see what it does often gives incomprehensible results on an analog scope. \$\endgroup\$
    – Bimpelrekkie
    Jul 5, 2017 at 14:19
  • \$\begingroup\$ @Bimpelrekkie Thanks ... I will give it another try (and if needed post a question again, with screenshots). \$\endgroup\$
    – Michel Keijzers
    Jul 5, 2017 at 14:29

1 Answer 1

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I guess you have a problem with triggering. Follow following 3 steps:

  1. Select correct trigger source. You probably have a choice between CH1, CH2, LINE, EXT. Select CH1 if the signal is picked up at channel1.
  2. Select correct trigger mode. You probably have a choice between AUTO, NORM, and a few other modes. If you select NORM the beam will only be visible if trigger is triggered (see 3.). If you use AUTO, you should always see the beam. So select AUTO.
  3. If you now see the signal but it is not standing still trigger is not tiggering; probably because the trigger level is beyond the signal range (i.e. too low or too high). So select an appropriate trigger level
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  • \$\begingroup\$ Thanks ... this I tried and I get either a single line (if the time is small enough) or a square wave (meaning alternating lines of 0 and 600 mV if recalling correctly). However, than I don't see vertical lines (which might be ok). However, when I make the time smaller, I eventually get a horizontal line, but in any case I never see a line 'going down' ... or are these test signals absolutely perfect? \$\endgroup\$
    – Michel Keijzers
    Jul 5, 2017 at 14:10
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    \$\begingroup\$ If the square wave signal has steep slopes it is completely what you expect that you don't see vertical lines! \$\endgroup\$
    – Curd
    Jul 5, 2017 at 14:19
  • \$\begingroup\$ I thought 'steep' would always be something in the 20 MHz scale? Meaning like microseconds, or should I think earlier about nanoseconds which is too fast for my scope to see? \$\endgroup\$
    – Michel Keijzers
    Jul 5, 2017 at 14:27
  • \$\begingroup\$ It is not about the that, the change between high/low on the squarewave takes very little time, even when the scope could easily follow that, the trace (bright dot) will spend very little time on that part of the screen so the phosphor gets almost no chance to light up. That's what is causing the faint lines. Have a look here: edn.com/Home/PrintView?contentItemId=4458052 and see what a square wave looks like on an analog scope. \$\endgroup\$
    – Bimpelrekkie
    Jul 5, 2017 at 14:31
  • \$\begingroup\$ I found out some new things about my oscilloscope and that helped (somewhat). I already knew about your tips (but still accepted it, since it was the only answer and might help others). \$\endgroup\$
    – Michel Keijzers
    Jul 8, 2017 at 18:26

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