Embedded Systems Conference
Breaking News
Blog

Assessing scope accuracy

NO RATINGS
View Comments: Newest First | Oldest First | Threaded View
sharps_eng
User Rank
Author
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
Author
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.

More Blogs
We need some mechanism to lower the temperature in political and social screaming matches, an also as a way to undermine echo chambers.
Soft starter technology has become a way to mitigate startup stressors by moderating a motor's voltage supply during the machine start-up phase, slowly ramping it up and effectively adjusting the machine's load behavior to protect mechanical components.
The newest storage innovations will change how things are done for the logistics chain, both upstream of the drive and array makers, and downstream in channels of distribution of their products.
Products that fall under a CE marking Directive cannot be imported into the EU unless they show the CE marking, which is simply a manufacturer's self-declaration that the product complies with the relevant European legislation.
Shaft sensors and their wiring make field-oriented motor control pricey, but sensorless alternatives are available.
Flash Poll
Like Us on Facebook

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Times on Twitter
EE Times Twitter Feed
Top Comments of the Week
March 2015 Cartoon Caption Contest: Mountain Climbing
March 2015 Cartoon Caption Contest: Mountain Climbing
The mountain had formed millions of years before when two tektronix plates collided.
208 comments