i have a Fluke 25 (had it for years), and a Owon PDS5022S digi o-scope (about a year old).

on a DC voltage the two devices read about 200mV difference. this is a issue for me because for some of my circuits i need resolution down to 1mV.

the Owon has a auto-calibrate feature, but just because it has that feature doesnt mean i trust it.

is it possible to use a precision voltage reference IC for calibration? or do you think i should have the Fluke calibrated by Fluke (or the like) and use a single meter for probing voltages??

 

It's an endless battle - get a precision source and it drifts over time, too. I would never use an o'scope for measuring voltage, though.

Resolution to a millivolt should never be a problem - do you perhaps means you need an absolute accuracy to a millivolt?

 

yes, accuracy.

why wouldnt you trust a o-scope for voltage, it should be accurate in freq as well as voltage, no? the all digital scopes should be more accurate that the older crt models....

 

Because Oscilloscopes were designed with different goals. Their display, if it is a CRT, has an inherent drift, and flatness of frequency response is a lot more important than measuring a voltage correctly. Even the cheapest, lowest level scope has a control to vary V/CM. A DVM, on the other hand, is meant to measure static levels. They may change, but if they vary very fast the meter is useless, so the AD converter was designed with that in mind.

Even digital oscopes are fundimentally analog devices, odd as that may sound. I would not use an oscope for a precision frequency measurement either, I have (several) freq counters for that.

 

Yes, you use an o'scope to see what is going on, but other instruments to measure the stuff. An o'scope is really good for comparing one waveform against another.