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Scope accuracy question ...

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BiOzZ:
Me and my friend are having a debate ... he likes to think his scope is about as accurate as it gets when it comes to voltage measurement (not waveform viewing or anything like that but SPECIFICALLY measuring voltage with/without even a waveform) but i think its no more accurate than a $100 DMM when it comes to voltage measurement

we both have ~$500 entry level 25mhz digital scopes and i doubt his re-branded rigol is any better than my owon when it comes to voltage measurement (or any other $500 scopes)
i dont have any > $100 DMMs to test this with and i dont want to lug it in to work to test this

what do you guys think/know?

i cant picture it using any different type of voltage reference than a $100 DMM for there $500 price! and i have never even thought of having my scope calibrated nor did i really think thats necessary as i dont really use it for more than measuring waveform voltage 0.1v resolution ... and i just count divs not even going in to measure really! but if it is some how more accurate there than a $400 fluke than fuck ill use that! XP

grumpydoc:
'scopes are generally not very accurate when it comes to voltage measurements - there again some DMMs aren't that accurate either.

Almost always it's an 8-bit ADC in a 'scope input so the resolution is limited to 0.4% anyway but the usual accuracy of a 'scope input is 1-2% for voltage, plus there will be some fall off in response with high frequency signals.

A cheap DMM might only be specified as 1% accuracy so they're in the same ball park. More expensive DMMs are usually better - 0.1% or even 0.05% can be had for $100 (e.g. UT61E is specified as 0.1% for DC voltage),

Edit: stylistically it's just wrong to use the word "typically" three times in two sentences....  so I fixed that :)

BiOzZ:
yeah that was around what i suspected ... i was unaware they would use 8 bit adcs vs like 10 bit adcs but still thats what i expected ... atleast out of a digital scope

Smokey:
Most real time scopes only use 8-bit ADC so they can keep the sample rate up and process all that data real time.  An oscilloscope is (typically) a general purpose instrument anyway and that is (typically) good enough.  Typically :)
One thing they can do though since they take readings really fast is seriously over sample slow signals and then average to get "higher resolution". 

tom66:
Rhode and Schwatz have a 14-bit scope, I think. But if you have to ask the price...

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