Oscilloscope inaccurate?

dakster

I just finished Activity #1 from chapter 7 of the understanding signals text, and I'm a bit confused about my measurements in the oscilloscope. The first pulse width should be 3ms, but when I measure it I get 2.64ms. For the 1ms logic 0 pulse, I'm measuring .88ms, and for the 2 ms logic 1 pulse, I'm measuring 1.6ms. Is this normal? I went through the calibration routine, and I'm getting the same measurements. Just wondering if this is a normal amount of variation.

I've seen similar variations in other measurements as well, but this one is particularly easy to see. I've attached a screenshot...

Beau Schwabe

dakster,

Zoom in to the signal and take another measurement... sometimes the granularity of the digital screen itself can cause rounding like this. I see this same sort of thing on a Tektronix Digital oscilloscope I have.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

dakster

I zoomed in pretty far for the measurement, with the same results this morning. I just zoomed out for that screenshot. Unfortunately I closed the book for the day, and took apart the circuit, so I can't reproduce it right now.