Author Topic: Can anybody explain me really how do works the time base of HP scopes 1740A and  (Read 10540 times)

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Offline SAUL BRITTO

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Tektronix 2220? I observed a sinewave of LG tv board that has 24 MHZ oscillator
 and 24 mhz was enough to  almost don't see  well the signal it was very tight. I did need to use X10 resource on the HP and on the tektronix 2220.Seems the full range of these scopes are divided in two steps,or it is a mistake? pardon my ignorance.
« Last Edit: February 27, 2016, 04:52:00 am by SAUL BRITTO »
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Offline tggzzz

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Tektronix 2220? I observed a sinewave of LG tv board that has 24 MHZ oscillator
 and 24 mhz was enough to  almost don't see  well the signal it was very tight. I did need to use X10 resource on the HP and on the tektronix 2220.Seems the full range of these scopes are divided in two steps,or it is a mistake? pardon my ignorance.

What do you mean "works"? Do you mean "use the timebase" or "internal operation of the tiembase"?

If you mean "use the timebase", then you need to produce a better definition of your problem, including the position of all controls and preferable a picture of the trace.

I have no idea what you might mean by "full range of these scopes are divided in two steps". My hp1740 has 23 steps (if I counted correctly).
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Offline rf+tech

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What Saul is referring to is the difference between main sweep and delayed sweep, that appear to him as two ranges. I no longer have an older scope with delayed sweep but seem to remember that there is a mechanical limit imposed upon main sweep when delayed sweep is lengthened. When delayed is set to 5 us/div then main sweep cannot be set faster.

24 MHz sine wave has a period of 41.67 nanoseconds. The fastest sweep of 50 nanoseconds/div should display 12 full cycles without the need to use 10X magnification.

@Saul, set the outer delayed sweep ring index mark to full clockwise stop (50 ns/div). It should now be possible to advance the inner main sweep to the full clockwise stop (50 ns/div).

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Offline SAUL BRITTO

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@Saul, set the outer delayed sweep ring index mark to full clockwise stop (50 ns/div). It should now be possible to advance the inner main sweep to the full clockwise stop (50 ns/div).

Yes,I did it but, I just think that the 24 MHZ 1/4 of full scale of a 100 MHZ scope,be so tight...

Thank you.
« Last Edit: February 28, 2016, 12:20:29 am by SAUL BRITTO »
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Offline SAUL BRITTO

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That way when I measure 80MHz'll just have something using X10.
« Last Edit: February 27, 2016, 11:33:24 pm by SAUL BRITTO »
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Offline SAUL BRITTO

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rf+tech look at this:

Is it normal? It is at full scale in main sweep, at 24mhz.
« Last Edit: February 28, 2016, 12:22:02 am by SAUL BRITTO »
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Offline tggzzz

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Is it normal? It is at full scale in main sweep, at 24mhz.
Since we don't know what you are probing, and since Chan1 and the timebase are both in the "uncalibrated" mode, who knows.

I suggest you turn the chan1 LED off using the  Chan1 cal pot, and the timebase LED off using the "sweep vernier" pot. If you are still having problems, post another picture and state what you would expect to be the displayed.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline SAUL BRITTO

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Is it normal? It is at full scale in main sweep, at 24mhz.
Since we don't know what you are probing, and since Chan1 and the timebase are both in the "uncalibrated" mode, who knows.

I suggest you turn the chan1 LED off using the  Chan1 cal pot, and the timebase LED off using the "sweep vernier" pot. If you are still having problems, post another picture and state what you would expect to be the displayed.

I noticed that  a 100mhz scope at 1/4 of your capacity is showing a sinewave  as if almost the end of  it's main time base.This signal that you see is a sinewave at 24 mhz with the timebase at .05 uSeg.
« Last Edit: February 28, 2016, 01:45:52 am by SAUL BRITTO »
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Offline rf+tech

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Saul,

When the timebase LED is on, the scope does not sweep at 50 ns/div. The sweep is slower and uncalibrated. I count 17.5 cycles of 24 MHz.
1/24e6 = 41.67 ns/cycle
17.5 x 41.67 = 729 ns total sweep time
729 ns / 10 divisions = 72.9 ns/div
Can you now see why the sweep is uncalibrated?

The same applies to the vertical amplifiers.

Quote
I just think that the 24 MHZ 1/4 of full scale of a 100 MHZ scope,be so tight...

Does full scale refer to horizontal scale or vertical scale? My interpretation is horizontal since the 10X magnifier is needed to see the individual cycles of 24 MHz.

To display 80 MHz across 10 divisions:
1/80e6 = 12.5e-9 = 12.5 ns per cycle
50 ns per division = 500 ns per sweep
500 ns per sweep / 12.5 ns per cycle =  40 cycles across 10 divisions

To clearly see the individual cycles requires faster sweep.

An important detail to consider: the stated bandwidth of a scope is that of the vertical deflection system. The horizontal deflection is less. For the HP1740A the horizontal deflection bandwidth is 5 MHz. At 50 ns/div x 10 divisions, the effective frequency is only 2 MHz.

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Offline SAUL BRITTO

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Oh thank you guys. But how to put off this led? I understand  many concepts about scopes and anothers I need help.
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Offline SAUL BRITTO

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OK I did it, Is like V CAL.

by tggzzz commentary I figured out that the vernier sweep of this scope is not working.
« Last Edit: February 28, 2016, 02:38:13 am by SAUL BRITTO »
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Offline SAUL BRITTO

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Does full scale refer to horizontal scale or vertical scale? My interpretation is horizontal since the 10X magnifier is needed to see the individual cycles of 24 MHz.

Yes rf+tech, is horizontal.

And my question is: it's normal a 100mHZ oscilloscope don't show a individual cycle of a 24 mHZ
sinewave,since it is at 1/4 of your capacity?
« Last Edit: February 28, 2016, 03:00:42 am by SAUL BRITTO »
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Offline rf+tech

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Saul,

Quote
by tggzzz commentary I figured out that the vernier sweep of this scope is not working.

Now that the sweep is "calibrated", 24 MHz should show 12 cycles across at 50 ns/div. Is this correct? If not correct and the error is large, then the vernier not working may be the cause for the large error.

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Offline SAUL BRITTO

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Ok sweep vernier working,was just a bad contact in a eight pins connector. A bit of w├╝rth spray  solved the problem!
« Last Edit: February 28, 2016, 03:39:49 am by SAUL BRITTO »
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Offline SAUL BRITTO

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Rf+tech I will count the cycles.
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Offline SAUL BRITTO

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Image after sweep vernier fix.
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Offline SAUL BRITTO

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rf+tech this is a signal of 1.5 KHZ 2Vpp T/DIV .2 ms.

« Last Edit: February 28, 2016, 04:41:14 am by SAUL BRITTO »
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Offline SAUL BRITTO

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Looking this same signal at the tek 2220 at 0.5 ms it fits exactly inside each graticule on the gridd of screen,how can I adjust the 1740A to the same condiction? I see that it is not right.
« Last Edit: February 28, 2016, 11:14:59 am by SAUL BRITTO »
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Offline rf+tech

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Saul,

Please do this simple calculation:

Period = 1 / Frequency

How much error exists between the measurement and the calculation?

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Offline SAUL BRITTO

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I did it= 0,000666667 In this image I am at 1,5 KHZ if period = 1/1500= 0.000666667  Sorry I AM HORRIBLE WITH MATH.



« Last Edit: February 29, 2016, 03:18:13 am by SAUL BRITTO »
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Offline SAUL BRITTO

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On my super donkey vision are 6 errors. Maybe 7.
« Last Edit: February 28, 2016, 09:20:07 pm by SAUL BRITTO »
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Offline tggzzz

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Not "having" arithmetic is a problem.

And it is time (seconds, s)  not conductance  (Siemens, S) .
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline SAUL BRITTO

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Thank you tggzzz
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Offline SAUL BRITTO

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rf+tech I count at 24 MHZ .05us 12 cycles but I will to post a new photo.
« Last Edit: February 28, 2016, 11:39:54 pm by SAUL BRITTO »
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Offline SAUL BRITTO

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F= 1/T = 1/0.00005=20000
1/20000= 0.00005us
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Offline SAUL BRITTO

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New photo that I think has 12 cycles:
« Last Edit: February 29, 2016, 04:00:34 am by SAUL BRITTO »
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Offline rf+tech

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Saul,

The photo actually shows 12.5 cycles across 10 divisions.

Look at the time marks at the arrows added to your photo.

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Offline SAUL BRITTO

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rf+tech about that your equation I did P= V.t
P= 24000000 x 0.00005= 1200 is it right? IF IT IS NOT RIGHT I see at least a 12 ratio,then on the anterior image there is an error of 5 cycles to more. Right?
« Last Edit: February 29, 2016, 04:48:12 am by SAUL BRITTO »
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Offline SAUL BRITTO

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Saul,

The photo actually shows 12.5 cycles across 10 divisions.

Look at the time marks at the arrows added to your photo.

RF+ Tech

Then I have to count that half cycle on the begin and on the end,how can I fix this rf+tech?
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Offline SAUL BRITTO

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Looks like after the sweep vernier fix it is a bit better.
« Last Edit: February 29, 2016, 04:20:30 am by SAUL BRITTO »
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Offline SAUL BRITTO

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I  am reading about this calibration but I still don't have a time marker,can I fix this problem with frequency counter and a good function generator?
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Offline rf+tech

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Saul,

Before jumping into sweep calibration, it is best to know some details about the accuracy of available signals.

What is the source of the 24 MHz signal? How accurate is this signal? Is it crystal controlled?

And the same about your function generator - how accurate is this? Is it synthesized or free running? Do you have a frequency counter?

Also, I see from your posts that you are having difficulty measuring time with an oscilloscope. What is to the left of the first vertical line is not counted.

Go back to the 24 MHz signal as shown in the photo with red arrows.
Position the bottom peak of the first cycle exactly on the first vertical display line.
Move the vertical position up so the bottom peaks are on the center line.
Count 12 bottom peaks and read the scale.
From the photo, this looks like 9.5 or 9.6 divisions.
How many divisions do you measure?
Now turn the sweep vernier from right to left.
Do you see many more cycles?
Turn the sweep vernier to the right (CAL position).
Does bottom peak 12 return to the same position?

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Offline SAUL BRITTO

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Ok I will do it.
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Offline SAUL BRITTO

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Saul,

Before jumping into sweep calibration, it is best to know some details about the accuracy of available signals.

What is the source of the 24 MHz signal? How accurate is this signal? Is it crystal controlled?

And the same about your function generator - how accurate is this? Is it synthesized or free running? Do you have a frequency counter?

Also, I see from your posts that you are having difficulty measuring time with an oscilloscope. What is to the left of the first vertical line is not counted.

Go back to the 24 MHz signal as shown in the photo with red arrows.
Position the bottom peak of the first cycle exactly on the first vertical display line.
Move the vertical position up so the bottom peaks are on the center line.
Count 12 bottom peaks and read the scale.
From the photo, this looks like 9.5 or 9.6 divisions.
How many divisions do you measure?
Now turn the sweep vernier from right to left.
Do you see many more cycles?
Turn the sweep vernier to the right (CAL position).
Does bottom peak 12 return to the same position?

RF+ Tech

Yes it is a crystal controlled oscillator.
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Offline SAUL BRITTO

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I have done these adjustments and got it better,but when a change the sweep time see small differences:
http://i65.tinypic.com/2z80vp3.jpg
« Last Edit: March 02, 2016, 05:42:58 am by SAUL BRITTO »
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Offline SAUL BRITTO

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1uSEC  I use 1mhz, 10uSEC 100KHZ and so on but,when I change the time to a near time I see that it does not keep completely stable there is a small difference
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Offline SAUL BRITTO

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I'm dabbing ice with this FG.
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Offline SAUL BRITTO

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I figure out my FG is deffective,seems a PS problem.
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Offline SAUL BRITTO

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Bingo! A cap in leackage and that a leakage wow!!!
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Offline SAUL BRITTO

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rf+tech what is the nomenclature for trigger offset on the HP scopes?
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Offline SAUL BRITTO

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rf+tech I have new photos and show you later.
« Last Edit: March 02, 2016, 09:15:40 am by SAUL BRITTO »
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Offline SAUL BRITTO

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I have done some comparisons with a tek 2220 that I have on the bench and they are very very near.
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Offline tggzzz

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Saul, you might find https://entertaininghacks.wordpress.com/library-2/good-questions-pique-our-interest-and-dont-waste-our-time-2/ helps you in the long term. Not all of the points apply to you, of course!

Do keep asking good questions. But this forum isn't twitter (as in https://www.google.co.uk/search?q=define:twit ).
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
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Offline SAUL BRITTO

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I apologize if I made a mistake or bothered in any way but, I'm new in the forum and really need some warnings. But, how to discuss an issue?
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Offline tggzzz

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I apologize if I made a mistake or bothered in any way but, I'm new in the forum and really need some warnings. But, how to discuss an issue?
No problem at all; no apologies necessary. You are honestly trying to learn, and that is good. The reason for pointing to that link is to help you get better answers.

Minor point: learn how to use the "quote" button, so people can understand what you are replying to.

More important point: think before posting, and where appropriate follow some of the guidelines noted on that page. Note that I don't always follow them!
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline SAUL BRITTO

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I apologize if I made a mistake or bothered in any way but, I'm new in the forum and really need some warnings. But, how to discuss an issue?
No problem at all; no apologies necessary. You are honestly trying to learn, and that is good. The reason for pointing to that link is to help you get better answers.

Minor point: learn how to use the "quote" button, so people can understand what you are replying to.

More important point: think before posting, and where appropriate follow some of the guidelines noted on that page. Note that I don't always follow them!

Thank you for your advice, was not my intention to cause this kind of event. I will be ever grateful when you advice me about my fails. I confess that I am still a little confused about the right way to act in the forum, will try to improve every day.
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Offline tggzzz

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I apologize if I made a mistake or bothered in any way but, I'm new in the forum and really need some warnings. But, how to discuss an issue?
No problem at all; no apologies necessary. You are honestly trying to learn, and that is good. The reason for pointing to that link is to help you get better answers.

Minor point: learn how to use the "quote" button, so people can understand what you are replying to.

More important point: think before posting, and where appropriate follow some of the guidelines noted on that page. Note that I don't always follow them!

Thank you for your advice, was not my intention to cause this kind of event. I will be ever grateful when you advice me about my fails. I confess that I am still a little confused about the right way to act in the forum, will try to improve every day.

As I told my daughter, "let's make new mistakes".

Do continue posting and asking questions!
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline SAUL BRITTO

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I apologize if I made a mistake or bothered in any way but, I'm new in the forum and really need some warnings. But, how to discuss an issue?
No problem at all; no apologies necessary. You are honestly trying to learn, and that is good. The reason for pointing to that link is to help you get better answers.

Minor point: learn how to use the "quote" button, so people can understand what you are replying to.

More important point: think before posting, and where appropriate follow some of the guidelines noted on that page. Note that I don't always follow them!

Thank you for your advice, was not my intention to cause this kind of event. I will be ever grateful when you advice me about my fails. I confess that I am still a little confused about the right way to act in the forum, will try to improve every day.

As I told my daughter, "let's make new mistakes".

Do continue posting and asking questions!
  :-DD

Ok thx.
« Last Edit: March 03, 2016, 04:31:12 am by SAUL BRITTO »
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