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Old 05-04-2013, 07:23 AM   #1
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Default Reading an Oscilliscope Display

This is for the relatively new ham operator. You more experienced hang back a few days, just drop a note to say you "Got it" so the newbies know it can be done.

Based solely on what you see in this display, describe the two signals in terms of voltage p to p and frequency.

Enjoy!

****

Just in case you have trouble reading the text, it says:

1 500 mV/
2 5.00V/
0.0S
500.0 microSec/
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Old 05-04-2013, 09:30 AM   #2
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Not enough information is give save that the frequency is the same.
And the peak to peak on the square wave is nearly 2x the sine wave, If I had to guess I'd say 1.7 but to figure that out I'd need to do more work than I plan on doing today. (blow up photo and measure)
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Old 05-04-2013, 02:45 PM   #3
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You are correct that the freq is same for both signals.

Now all you need is volts/division for the 2 signals, which is displayed. And the v/div is different for both signals.

Here's what you are looking at: The channel 1 signal is a sine wave being fed into a differential amplifier, which is being overdriven to the point of clipping, which produced the square wave output on Channel 2.

But it is all there, 2 sets of volts/div and (of course) one set of time/div (and 1/time equals freq.)
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Old 05-06-2013, 06:08 PM   #4
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OK, count the divisions, do the math and tell us what you see.
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Old 05-07-2013, 03:56 AM   #5
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Square wave is about 8v p/p
Sine wave is 5v p/p
They are 180 out of phase
Could be wrong, haven't read one of these in over 10 years.



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Old 05-07-2013, 09:07 AM   #6
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Sinusoid: 1v p-p, about .35v rms, 1 KHz
Square wave: 25v p-p, 12.5v rms, 1 Khz
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Old 05-07-2013, 05:27 PM   #7
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Really? I always thought RMS = pp x .707 or if you wish, pp/1.417 or there abouts.
But you did read the scope right.



And here's where I got all this stuff:

http://en.wikipedia.org/wiki/Operational_amplifier

Refreshing the ol' brain for a test I will need to take to get a promotion at work.
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Old 05-07-2013, 08:13 PM   #8
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Quote:
Originally Posted by Radio View Post
Really? I always thought RMS = pp x .707 or if you wish, pp/1.417 or there abouts.
But you did read the scope right.



And here's where I got all this stuff:

http://en.wikipedia.org/wiki/Operational_amplifier

Refreshing the ol' brain for a test I will need to take to get a promotion at work.
RMS for a sinusoid is 0.707 times the peak-to-peak, which in this case is .707 times 2v, not 1v, so the RMS for this sinusoid is about 1.414 volts, and I was off by a factor of two. Oops, I used the peak value instead of the peak-to-peak.

This square wave, which is not a sinusoid, is always either 12.5v positive or 12.5v negative; so it has the same heating effect on a resistor as 12.5v dc. Its RMS value is 12.5v because it's a square wave and not a sinusoid.

Back when I made my living as a circuit design engineer, I must have designed hundreds of circuits using 741 op-amps and their predecessor the Fairchild 709 -- both created by my personal hero of the time, Robert J Widlar, and his sidekick James N Giles. Your Wiki link brought back memories. Widlar left Fairchild for National Semiconductor, demanded a piece of the action, and got stinkin' rich when NSC took the market away from Fairchild.
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Old 05-08-2013, 05:38 PM   #9
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Quote:
Originally Posted by NN5I View Post
James N Giles. Your Wiki link brought back memories..
When I was a child I would watch in fascination when "Mr. Giles" would come to our house to repair a television. Never new his first name. Just Mr. Giles, the TV man. I guess I was in kindergarten when he laughed at me, quite roundly, when I inquired if my grandmothers little Admiral black and white TV was out of film.

Years later I helped build a ground network for NASA, and one day was given a quick tour of the Vehicle Assembly Building. Standing there looking up into the engine bells of Discovery, I thought "Gee, I wish Mr. Giles could see me now."
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Old 08-22-2014, 10:20 PM   #10
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Quote:
Originally Posted by NN5I View Post
RMS for a sinusoid is 0.707 times the peak-to-peak, which in this case is .707 times 2v, not 1v, so the RMS for this sinusoid is about 1.414 volts, and I was off by a factor of two. Oops, I used the peak value instead of the peak-to-peak.

This square wave, which is not a sinusoid, is always either 12.5v positive or 12.5v negative; so it has the same heating effect on a resistor as 12.5v dc. Its RMS value is 12.5v because it's a square wave and not a sinusoid.

Back when I made my living as a circuit design engineer, I must have designed hundreds of circuits using 741 op-amps and their predecessor the Fairchild 709 -- both created by my personal hero of the time, Robert J Widlar, and his sidekick James N Giles. Your Wiki link brought back memories. Widlar left Fairchild for National Semiconductor, demanded a piece of the action, and got stinkin' rich when NSC took the market away from Fairchild.
I think at one time this was a question you had to know to pass your Technician Class License exam, later it was moved to the General Class exam. Today, the exams are so dumbed down, about all you have to do is speel your name right on the application to get your Technician Class License.
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Old 08-22-2014, 10:37 PM   #11
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Stories of NASA -

I worked for a local machine shop - MWM Machine - http://www.millerwelding.com/

We had a big flood in 1996 and the machines I ran still had dirt, mud, water inside of the electric motors and gear boxes two years later.

They would take one or two at a time off line, tear them apart, refurbish them and then put them back together again.

One of the Millwrights - Sam the Garlic Man, was sitting on the table of a boring mill at lunch time and Jimmy Broom asked him why there was a hole in the middle of his boring mill table, and none of the other mills had this hole.
They were all G&L 4 inch mills.

Sam fessed up that he was working one Sunday night by himself and was operating 3 different machines by himself. Sam got the first two running and was working on setting up a job in the lathe and forgot about his cut.
When he came back, the cutter had gone through the bed of the machine.

When Jimmy asked him if he caught heck or was fired for doing this Sam exclaimed that the owner had nothing to say because he was making them a lot of money when he was operating 3 machines at the same time.

Sam worked for NASA during the Space Program in the 1970's and 80's and was the engineer that thought up piggy backing the Space Shuttle on the outside of the 747...

Sam planted a crop of garlic and a local buyer gave him $40 a lb for it and told him that he would buy all that Sam grew the following year.
So Sam planted a 20 acre field at his farm the next year and then the buyer refused to buy his crop unless he cleaned it and threw away the smaller bulbs.
SaM dumped the whole crop behind his trailer and got out of the garlic business.
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Old 08-23-2014, 07:16 AM   #12
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Quote:
Originally Posted by Mr. Ham View Post
... about all you have to do is speel your name right ...
I guess you'd be in trouble if your name was Spell. I used to live next door to a family named Spell. Their kids spent more time in my house than in theirs, and we're still friends 35 years later.
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Old 08-23-2014, 07:55 AM   #13
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I also figured out the frequency is the same and the Square wave was around about 2x the height of the sine.. (You said already the amplifier settings are different)

I assume the numbers across the top of the screen are significant to frequency and voltage but as I have never seen a scope that had those.. They are meaningless to me.

IF I had ever used that scope... the meaning would be remembered.

I do recall in Electronics class (AC) we built a small oscillator and then added modulation.. I thought the scope trace looked,,,, funny.. So I swapped a couple of leads and proved it... Then trouble shot the circuit to find what was wrong and fixed it.. Impressed the heck out of my lab partner.. Teacher (A fellow ham) Knew exactly what I did (Went from a time based display to a trapezoid display which is audio cycle based instead of time). He was somewhat more impressed with my ability to trouble shoot though.
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