Where to read trace on analog oscilliscope? - Page 1
Forum section: electronics / testgear

author: corrado33
author_rank: Frequent Contributor
timestamp: October 08, 2013, 08:54:45 pm
content: Was watching #502 the other day and it occurred to me, I don't know where to read a trace on an analog microscope.Is it in the middle of the trace or at the extremes? I've never honestly thought about it, but now that I have I'd say it would probably be at the middle, is that correct?

author: w2aew
author_rank: Super Contributor
timestamp: October 08, 2013, 09:10:36 pm
content: Quote from: corrado33 on October 08, 2013, 08:54:45 pmWhat do you mean "read a trace"? The question doesn't make sense to me... Can you be more specific on what you're asking?

author: corrado33
author_rank: Frequent Contributor
timestamp: October 08, 2013, 09:52:07 pm
content: By "read a trace" I mean, if you are looking at the scope, you see your waveform on the screen. The waveform will have a certain thickness depending on the focus and intensity, where, along that thickness, do you read?Example,Say you have a 4V peak to peak sine wave. In ideal conditions, on the display, with 1V/division, it would measure 4 divisions up/down. (Obviously). Now, assume the wave "thickness" is 1mm and the division lines on the scope are .5mm. That would mean, assuming everything is dead on, that .25mm of the waveform would be above the line at .25mm would be below. This describes the situation where you would read the middle/center of the trace.If it is correct to read the "extreme" of the trace, instead of .25mm being above and .25mm being below the division on the scope, you'd have 0mm above the division and .5 below. I can make a diagram if needed.EDIT: I apologize, read a "trace" comes from my research where we call the lines on the graph "traces," so I just use the word trace to represent any waveform I see.

author: EEVblog
author_rank: Unknown
timestamp: October 08, 2013, 09:56:41 pm
content: Quote from: corrado33 on October 08, 2013, 08:54:45 pmStrictly speaking, yes, in the middle.Some scopes have really thick traces which can make that a pain, but analog scopes aren't really precise instruments anyway, so the point can often be moot on a nice sharp trace scope.

author: tonybarry
author_rank: Contributor
timestamp: October 09, 2013, 12:54:06 am
content: Hi Corrado,In the event you want to be as precise as you seem to imply, your only solution is to inject a known voltage into the scope, and read off the graticule ... and then make a choice as to what is more precise for you. An edge is generally easier to pick than the middle of a line. But ...If the Y-amp is well calibrated, then your trace will be close to where you expect it, and the graticule will line up pretty well ... and then you pick which edge or the middle is closest to your expected mark.However, this is possibly taking the Y-amp precision into regions where drift and thermal effects and probe bandwidth and all kinds of stuff will destroy your precision much more than the thickness of a scope trace.Accuracy and precision do not come cheaply.Regards,Tony Barry

author: w2aew
author_rank: Super Contributor
timestamp: October 09, 2013, 01:33:16 am
content: Quote from: corrado33 on October 08, 2013, 09:52:07 pmAh, now I understand what you meant. And, you've gotten good opinions already. Of course, we do call them traces too.

author: ve7xen
author_rank: Super Contributor
timestamp: October 09, 2013, 02:45:23 am
content: I think the confusion might stem from the fact that you wrotemicroscopein your OP.Quote from: corrado33 on October 08, 2013, 08:54:45 pm

author: van-c
author_rank: Regular Contributor
timestamp: October 09, 2013, 04:10:35 am
content: If cursors are being used to measure a voltage difference, it is sometimes easier to align a horizontal cursor with the trace if the measurement is done from, say, the bottom edge of the trace and to position the cursor right at the bottom edge of the trace too. Here, the cursor dots will be visible right at the trace edge. If the center of the trace is used for the measurement, the cursor can be obscured by the trace itself, introducing some uncertainty of the cursor location, especially if the trace is very thick.However, as has been said, most analog scopes are not typically precise enough for this hair splitting to make a lot of practical difference. But being able to clearly see the cursors, and even the graticule lines, aligned with the trace edge makes me feel like my measurements are a bit more "scientific".--Van

author: corrado33
author_rank: Frequent Contributor
timestamp: October 09, 2013, 04:17:10 am
content: Quote from: ve7xen on October 09, 2013, 02:45:23 amHa, I didn't even notice, must have been thinking of the microscope in the lab. I AM, however, talking about oscilloscopes.I'm not actually looking for accuracy, we have plenty of very nice digital scopes in the lab that I could use if I really wanted to, I was just wondering. I don't use oscilloscopes in my daily research, but the lab I'm in used to be an electronics lab, so we have lots of old electronics equipment that's fun to play with every once in a while.