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Fundamentals questions about my Scope.

Discussion in 'General Electronics Discussion' started by Balrock, Jul 14, 2012.

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  1. Balrock


    Mar 1, 2012
    Scope model ATTEN ADS1102CAL

    I have been studying about OP Amps for several weeks but I am confused about what my scope is telling me. So I have a few fundamental questions.

    1 - Poor Display.

    1.a Notice the poor visual display of the waveform on channel 1 at 1V per division
    1.b Wave looks better at 500mV per division.

    Q. Would this just down to the “budget” quality of my scope or more, like mains hum?

    2 - Looking at weak voltage signals

    2.a CH1 96mV input to Op Amp. CH2 output of Op Amp of 1.28V.
    The 96mV is derived from a voltage trimmer on my Analogue Development board.
    2.b The same thing but voltage is derived from a very low value resistor GND side of a potential divider on a PC-SMPU.

    While the numbers look ok (I think) the display is a mess.

    Q Why? Am I suffering from not setting my scope up correctly or poor measuring conditions.

    Thanks, Paul.

    Attached Files:

    • 1a.gif
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    • 1b.gif
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    • 2a.gif
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    • 2b.gif
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  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    I don't know that particular model of scope. Nevertheless, some answers:

    1) I don't see anything wrong with the display as you show in attachments 1 and 2. The difference is just due to the higher resolution at 500mV/division which uses more space on the display to show the waveform. There seem to be some quantizing errors which may be due to the low vertical resolution (8 bit) of the scope.
    Does channel 2 show the same symptoms? If not channel 1 may be defect.

    2) The signals in attachment 3 look o.k. In attachment 4 you use 25* the resolution compared to attachment 3 (20 mV/div as compared to 500mV/div). Also you monitor the voltage from a switched mode power supply. These voltages always have ripple and noise on top of the DC. This is an inherent property of switched mode power supplies (Google >switch mode power supply noise<). So the scope probably displays the noise from the PSU.
    The numbers are computed by averaging the signal (or RMS computation). These methods inherently filter out the noise (it's a property of the math behind).

  3. Balrock


    Mar 1, 2012
    Thank you Harald. Much appreciated.
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