Digital Oscilloscope Maximum Input Voltage

[mike_mike]

I set the probe and the oscilloscope to 10x. In the previous images, the oscilloscope and the probe were at 1x in the first image while in the second image the oscilloscope and the probe were at 10x.

[nrxnrx]

Does it behave the same with another probe?

It may be that the switch is faulty (either the switch itself or the plastic cap has crap remaining from moulding).

[mike_mike]

Yes. It behave the same with another probe.
It behave the same on both channels of the scope.

[nrxnrx]

Well, either both your probes are stuck in 1x or 10x mode, or your scope is. Try probing a known voltage like a battery.

--
Mihai

[mike_mike]

I tried to measure a 9V battery.
The oscilloscope measured 1.2mVpp the noise of the battery on 1x (the probe and the scope were set on 1x) and 12mVpp the noise of the same 9V battery on 10x (the probe and the scope were set on 10x).

[tautech]

I tried to measure a 9V battery.
The oscilloscope measured 1.2mVpp the noise of the battery on 1x (the probe and the scope were set on 1x) and 12mVpp the noise of the same 9V battery on 10x (the probe and the scope were set on 10x).

In AC coupling all you are seeing is internal scope noise, there is NO noise on pure DC.

[mike_mike]

Thanks for the reply.
So I think my scope is not working correctly ? because it shows 50mVpp in 10x mode while in 1x mode it shows 5mVpp ?

[tautech]

Thanks for the reply.
So I think my scope is not working correctly ? because it shows 50mVpp in 10x mode while in 1x mode it shows 5mVpp ?

Unless it was in front of me and I was driving it, I couldn't/wouldn't say.
Spend some time here watching Alan's vids:
https://www.eevblog.com/forum/beginners/oscilloscope-training-class-(long)/

Are you using the probe ground lead ?

[nrxnrx]

Switch the scope channel to DC coupling and measure the 9V battery.
Set the scope to expect a 10x probe. Measure the battery when the switch on the probe is set to 1:1 and 10:1 (do not change the scope settings during this). What voltage does the scope see?

If the displayed voltage doesn't change when you flip the switch on the probe, the fault lies with the probe.
If so, and it shows 9V, then your probes are stuck in 10:1 mode. If it shows 90V, they're stuck in 1:1 .

[mike_mike]

Are you using the probe ground lead ?

Yes.

If I set the coupling to DC, the scope setting to 1X the vertical voltage to 5V, if I use the probe with 1X the voltage goes to nearly 10V and when I use the probe with 10X the voltage goes just a little bit above the initial position of the trace.

[David Hess]

The maximum input voltage is 300V peak as it is mentioned in the manual ?

Yes, it applies to a 1:1 probe or direct cable connection.

It also applies to 10x probes that do not include an internal shunt which is practically all of them.  If you use a 10x probe and set the input coupling to AC, then the coupling capacitor will charge to the *unattenuated* DC voltage at the probe tip so 300 volts peak is still the maximum input voltage.

This same restriction applies to high voltage 100x probes that do not include an internal shunt which again is practically all of them.  1000x probes include an internal shunt.

[mike_mike]

Thanks for the reply.
The x1 and x10 probes are the same with 1x and 10x probes ?
Is the same thing if I say x1 and x10 or 1x and 10x ?

[David Hess]

The x1 and x10 probes are the same with 1x and 10x probes ?
Is the same thing if I say x1 and x10 or 1x and 10x ?

Yes, they are the same thing.  Some manufacturers write it one way and some write it the other way.  I prefer writing 1x and 10x to avoid capitalization of the "x" at the beginning of a sentence.

[mike_mike]

While de coupling is set to DC, if I put the probe to the ground clip, it is normal to appear noise on the screen ?
For example if I set the scope and the probe to 1x, the peak to peak voltage of the noise is about 800uVpp and while the scope and the probe are set to 10x the noise is about 8mVpp.
Is that normal ?

[David Hess]

While de coupling is set to DC, if I put the probe to the ground clip, it is normal to appear noise on the screen ?
For example if I set the scope and the probe to 1x, the peak to peak voltage of the noise is about 800uVpp and while the scope and the probe are set to 10x the noise is about 8mVpp.
Is that normal ?

DC or AC coupling should not matter and that noise is normal.

The bandwidth at the probe tip is high enough to pick up interference through the loop area of the ground lead.  If you short the probe tip to the collar to reduce the loop area, then the interference should be reduced practically to zero and coaxial connections to the probe tip without the ground lead are often used for only this reason.  A 10x probe will pick up more interference than a 1x probe because of its lower input capacitance and higher bandwidth.

[Damianos]

@mike_mike
By studying the oscilloscope manual you will find the right answers to your questions.
For example:
- the absolute maximum input voltage on the connector is 300V, regardless of the selected vertical range (page 9, 124 and the front panel of the instrument).
- the AC input coupling is there for exactly what you want to do: it separates AC signals that are DC biased (page 82-83).
- there is not any distinction depending on the coupling mode for the input impedance, so when using a division probe (x10, x100) the ratio is always the same.
- it is referred two times the "probe compensation", in the "setup" and the "maintenance" sections, don't overlook it, affects the AC response of the system (the probe is part of the instrument).
Measuring low level signals needs a careful setup to avoid traps, such as interference.

Follow the manual, keep notes for what seems difficult to understand, continue asking and learn how to filter the answers that you get!

[mike_mike]

Thanks for the reply.
I saw another thing on my oscilloscope: if I set the time base to 25mS/div there appear a delay of the signal on the screen. So when I rotate the knob for the time base to 25mS/div, there appear a delay until the trace appear on the screen. If I set the time base to 5mS/div there is almost no delay. If I set the knob for 10mS/div the delay is smaller than the delay for 25mS/div. This happens on both channels. The probe is not connected to any signal source while I do these things. The voltage/division is 20mV/div.
Is that normal ?

[Damianos]

Yes, it seems that is the "normal" annoying operation that most (if not all) oscilloscopes do. They "update" the memory contents using the selected time base and then wait for a trigger event. I don't know why they do not simply discard any memory content faster.

[David Hess]

Unless the DSO is operating in roll or scan mode, the display is only updated after the record is filled *after* the trigger event.  So if the trigger is in the middle of 10 horizontal divisions, the 5 horizontal divisions to the right of the trigger point have to fill before the display is updated and at 25ms/div that is 125 milliseconds.  I assume DSOs that have a huge number of horizontal divisions update the display based on only the display record because waiting for 5000 divisions to fill would be annoying.

Roll and scan mode have no trigger so the display is updated immediately.  Roll mode is like a strip chart recorder.  Scan mode scans the display from left to right and then repeats.

[mike_mike]

Thanks for the reply.
I made a video with the calibration signal
I noticed that there is a delay from the moment I connect the probe to the calibration signal and the moment when the signal appears on the screen. Also there is a delay from the moment I disconnect the probe and the moment when the signal disappears from the screen. Is that normal ?

[David Hess]

I noticed that there is a delay from the moment I connect the probe to the calibration signal and the moment when the signal appears on the screen. Also there is a delay from the moment I disconnect the probe and the moment when the signal disappears from the screen. Is that normal ?

That is the same delay I discussed.  The display is only updated after the record is filled.

[mike_mike]

Thanks for the reply.
I saw another thing on my oscilloscope: while I am measuring the output of an LM317 + pnp transistor power supply I see on the screen a signal with the peak to peak voltage about 70mVpp measured by the scope, but when I am measuring the signal on the screen using the grid, the waveform has an peak to peak amplitude of about 55-60mVpp. While I am measuring this the time base is set on 2.5nS, and the voltage/div is set on 20mV. Is that normal or my scope does not measure correctly ? 

Later Edit: I think I found the problem. I tried to measure again and it seems that the scope measures voltage correct.

[mike_mike]

What acquisition mode should be used on the oscilloscope ? I can choose between Normal, Average and Peak Detect. Which is the best ?
Also, when I am using Average I can select a number from 2 to 256. If I select 256, the trace is at first very noisy and it getting less noisy in a few seconds:
Average 256, when I connect the probe to the LM317 power supply:
https://imgur.com/a/LE8ZF
Average 256, after about 10 seconds:
https://imgur.com/a/MWcZr
Average 256, after about another 10 seconds:
https://imgur.com/a/QfPwn

It is normal for the trace to be more noisy at the moment when I connect it to the signal source ? And after a few seconds to get less noisy ?

[tggzzz]

What acquisition mode should be used on the oscilloscope ? I can choose between Normal, Average and Peak Detect. Which is the best ?

Each is best in different circumstances. That is all explained in many places on the web; I suggest starting with Tektronix and Agilent application notes.

There's no point in us spending our precious time giving a (poor) explanation to you, if you can't be bothered to spend some time finding high quality answers. Google is your friend.

[mike_mike]

Thanks for the reply.
When measuring the noise from an LM317 or LM723 power supply, I saw that in one day, the noise was about 24mVpp for the LM723 power supply and about 50mVpp for the LM317 power supply. A few days later, I measured again the noise from the same power supplies, and I found that the LM723 had noise about 40mVpp and the LM723 had noise about 55mVpp. Is that normal ? Why the noise whas lower in one day and higher in another day ?