Design Con 2015
Breaking News
Comments
Newest First | Oldest First | Threaded View
sharps_eng
User Rank
Rookie
re: Assessing scope accuracy
sharps_eng   2/20/2012 9:57:12 PM
NO RATINGS
You have to be careful when doing differential measurements (x-y) with the iNVERT function, there is no standard for where the summing takes place. Many (all?) cheap LCD scopes just subtract the pixels, so although what you see is what you get, if one of the signals clips the screen edge the diff signal is meaningless. Decent analog scopes (and some were quite cheap also) used to let you have seriously high gains which would overload each channel on their own, but when summed, cancelled the inputs so that you could get a good high-resolution view of a small signal which was superimposed on a large one (like a 100mVp-p crosstalk transient on a 24V DC supply). Its worth checking this on any scope purchase. Of course, you will eventually build a decent diff pre-amp yourself, but until then, a good ADD-plus-INVERT on your scope is very handy.

Bert22306
User Rank
CEO
re: Assessing scope accuracy
Bert22306   2/20/2012 9:01:23 PM
NO RATINGS
That's kind of an age-old question. It's not JUST about accuracy. It's also about whether you change the measurement appreciably by just touching probes to the circuit. IMO, every EE who's actually an EE has had this drilled into him throughout school and career, and has been bitten when he ignored the issue. Sometimes the absolute number isn't all that important, but what always matters is whether the scope, voltmeter, ammeter, whatever, is making the measurements irrelevant. Sort of a macro version of Heisenberg's uncertainty principle.



Flash Poll
Top Comments of the Week
Like Us on Facebook
EE Times on Twitter
EE Times Twitter Feed

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Life
Frankenstein's Fix, Teardowns, Sideshows, Design Contests, Reader Content & More
Max Maxfield

DIY Practical Joke Project Idea
Max Maxfield
1 Comment
I just received a rather interesting email from a member of the EETimes community who prefers to remain anonymous. This message was as follows:

Jolt Judges and Andrew Binstock

Jolt Awards: The Best Books
Jolt Judges and Andrew Binstock
1 Comment
As we do every year, Dr. Dobb's recognizes the best books of the last 12 months via the Jolt Awards -- our cycle of product awards given out every two months in each of six categories. No ...

Engineering Investigations

Air Conditioner Falls From Window, Still Works
Engineering Investigations
2 comments
It's autumn in New England. The leaves are turning to red, orange, and gold, my roses are in their second bloom, and it's time to remove the air conditioner from the window. On September ...

David Blaza

The Other Tesla
David Blaza
5 comments
I find myself going to Kickstarter and Indiegogo on a regular basis these days because they have become real innovation marketplaces. As far as I'm concerned, this is where a lot of cool ...