Author Topic: Can anybody explain me really how do works the time base of HP scopes 1740A and  (Read 10623 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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Online 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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Online 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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Online 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.
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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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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