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Fundamentals of Oscilloscopes Slide 50

The oscilloscope screen shot on this slide shows the effect of the inductance of the probe ground lead. As the ground lead length increases its inductance also increases, causing an ever increasing amount of distortion. The waveform on the extreme left, the olive green trace, is measured with a standard length ground lead. It has the highest amount of overshoot, approximately 36.6%. The second capture, brown, used a high frequency compensated ground lead and the overshoot was reduced to 26.6%. The third trace, blue, illustrates the use of a ground spring, which is really short. This reduced the overshoot to 17.6%. The final two, light green and red, are the best, using the ground blade and a probe head ground achieved an overshoot of 16.3% and 10.1% respectively. The 10.1% overshoot is very close to being an accurate representation shape of the actual signal overshoot. This is a good example of why it is important to keep the grounds as short as possible to transfer the true wave form into the oscilloscope.

PTM Published on: 2012-06-11