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Oscilloscope Tutorial

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Oscilloscope Tutorial

Postby Carlo » Tue Nov 14, 2006 2:37 pm

Hi all,

I'm in the market for an oscilloscope. I started reading the Oscilloscope Buyer's Guide: What to look for when choosing an oscilloscope.

In the section labeled as Resolution and Accuracy, how do you get 8 mV per step with an 8 bit resolution?

Also, regarding real time and equivalent time sampling rates, if I have a repetitive signal (e.g. a 1 kHz tone) that is switched off suddenly at intermittent times, do I give priority to the real time sampling rate when picking an oscilloscope?


Postby Michael » Wed Nov 15, 2006 4:00 pm


Thank you for your enquiry.

The ±1V range will give you an 8mV step performance with 8bits. The 8bit range will give you a minimum ±100mV range, this would give you 0.78mV steps.

This would largely depend on the length of the full pulse. High memory scopes remove the compromise between capturing the full pulse and reducing the sampling rate. With our new PicoScope 5000 series, the high memory and sampling rate allow you to view slower signals, like your 1kHz tone, over much longer periods of time. This is even possible with the 3000 series. All of this without even switching the ETS mode on!

If you choose a scope with a much higher sampling rate, you can oversample to improve the effective resolution.

Without my advice appearing biased, I would always recommend that you consider future applications as well as current ones when choosing a scope.

If you have any further questions, please don't hesitate to ask.

Best regards,
Michael - Tech Support
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Re: Oscilloscope Tutorial

Postby Jeff » Wed Dec 20, 2006 12:42 pm

Carlo wrote:In the section labeled as Resolution and Accuracy, how do you get 8 mV per step with an 8 bit resolution?

Hi Carlo,

The article you read says that "with a ±1 V range selected", 8 bits gives you 8 mV steps. This was calculated as follows. The voltage swing on a ±1 V range is from -1 V to +1 V, which is a total swing of 2 V. The number of levels at 8-bit resolution is 2^8 = 256. The voltage resolution, or voltage step per level, is therefore 2 V / 256 = 7.8125 mV, or nearly 8 mV.
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