| Electronics > Projects, Designs, and Technical Stuff |
| Why are oscilloscopes so inaccurate? |
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| Siwastaja:
--- Quote from: soldar on August 10, 2019, 11:02:37 am ---How on earth do you measure a voltage on a scope screen with better than 1% accuracy? Does it involve a microscope? --- End quote --- It involves reading out the number from the screen. You know these digital storage oscillosscopes that really penetrated the market in the 1990's. |
| bd139:
Scopes are shit at everything they do. They just do a lot of shit things at the same time which turns out is a lot more useful than things that do one thing really well. |
| magic:
The analog frontend could probably be fitted with a DC servo, frontends of cheap DSOs already use separate paths for high and low frequencies. Attenuators could be measured and calibrated digitally during self-calibration. Thermal stability of variable gain amplifier ICs and ADCs remains a question. Some scopes are so bad that they could use improvements even with zero hardware cost. My Hantek doesn't calibrate gain errors in various ranges in self-cal, they just don't match each other no matter what. |O |
| ogden:
--- Quote from: soldar on August 10, 2019, 11:02:37 am ---A lawnmower and a nail clipper are both cutting tools but I would not use a lawnmower to trim my fingernails --- End quote --- And on that bombshell we end this thread :D |
| 2N3055:
They are not. I have a scope that has 0,25% guaranteed accuracy. It is 16 bit. General purpose scopes are 8 bit. Their resolution is roughly 0,4%. That is smallest voltage step they are capable of. There is also DNL and INL in A/D converter, meaning, each step is not exactly 0,4%... To keep specs under control, best they can promise is 1 -1,5% (some manufacturers do), with everything being ideal. Which is not. Also it is really hard to make front end that has bandwidth from DC to 1GHz with max 1-2% total amplitude error. 6,5 Digit DMMs have approximately 23-24 bit resolution. And rest of meter specialized and optimized for just that. |
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