My New Scope's Accuracy? - Page 1
Forum section: electronics / beginners

author: tony3d
author_rank: Frequent Contributor
timestamp: December 01, 2013, 06:31:37 pm
content: Hi all, I just took delivery of my first scope. It's an Owon SDS-7102. The first thing I noticed was that the accuracy wasn't that great. If I set my Korad power supply to say 15.00volt, channel 1 will read 15.02, and channel 2 15.08. My multimeter will read 15.003. Why is it so far off? I have the system setup for X10 on both the menus, and the probes. Is this normal? So far everything else seems to be working well.

author: Lightages
author_rank: Unknown
timestamp: December 01, 2013, 06:35:07 pm
content: Yes it is normal. Scopes are usually only rated for around 3% accuracy.

author: tony3d
author_rank: Frequent Contributor
timestamp: December 01, 2013, 06:53:30 pm
content: Is the variance between channels normal?

author: PA4TIM
author_rank: Super Contributor
timestamp: December 01, 2013, 06:59:13 pm
content: This sort of specs are be in the manual or spec sheets. Or at least they should be there. Also what they do not list is informative, most times that is because they do not want to list them and this is not because they are better as the competition ;-) Also watch out for things like typical, best or max. Many over read things like max/min because good brands tell you the worst case. So max 2% means you can be Lucky and have 1% but I have seen specs for cheap gear that list somethig as min 2%. And that means that if you are Lucky it is 2% but yours can be 5% as well.A good scope is most times around 2 or 3% for vertical. But also the time/div and every other parameter has tolerances.Including amplitude, Phase difference and crosstalk between channels. Thios must be in the manual and if not, then it will probably not be very good.

author: Rufus
author_rank: Super Contributor
timestamp: December 01, 2013, 07:01:13 pm
content: Quote from: tony3d on December 01, 2013, 06:31:37 pmThe scope only has 8 bit ADCs so the resolution is only 0.4% never mind accuracy.

author: tony3d
author_rank: Frequent Contributor
timestamp: December 01, 2013, 07:21:08 pm
content: Quote from: Rufus on December 01, 2013, 07:01:13 pmSo then this is pretty normal for this grade of scope. Should be fine as a beginner hobbyist scope I guess. I really like it so far. The screen is great! Overall build is not bad at all, as is the front panel layout. Not crazy about the menu system, but I'll get use to it.

author: Rufus
author_rank: Super Contributor
timestamp: December 01, 2013, 07:53:08 pm
content: Quote from: tony3d on December 01, 2013, 07:21:08 pmIt is normal for 'high' grade scopes. Fast ADCs are expensive. You don't need more resolution than vertical pixels you are going to display. The digital read outs are just a convenience the difference between 15.02 and 15.08 is probably 1 ADC bit.

author: tony3d
author_rank: Frequent Contributor
timestamp: December 01, 2013, 08:30:46 pm
content: Ok, thanks everyone. Just wanted to make sure it was normal behavior. Now I can get into enjoying it. I've been able to get it all setup displaying the information I want to see. I adjust the probe's and ran the self calibration. Now to find some good tutorials. My wife ordered me a cheap ($104) Velleman function generator for Christmas. I really hope it's ok to leave the battery in the unit all the time, removing, and installing it is a pain! Other than that at $365.00 it's a pretty good deal.