Digital Oscilloscope Maximum Input Voltage

[mike_mike]

Dear Forum,

I recently bought a new GDS-1052-U oscilloscope. I read a few pages from the oscilloscope manual and I found that the maximum input voltage is 300Vpeak.
I have a question regarding the maximum input voltage: 300V peak is the maximum voltage input for 10V/div or for 2mV/div using a 1x probe and AC coupling ?
The oscilloscope will be damaged if I set the vertical voltage to 2mV/div and connect the 1x probe to 200V peak ? I know that the 200V peak voltage cannot be displayed on the screen if the vertical voltage is 2mV/div, but I want to know what can happen ?
The last questions: what is the maximum DC input voltage, using a 1x probe and DC coupling ?
Thanks in advance,
Mike

[zvonex66x]

Maximum input voltage is 300V no metter if you set scale for 10V/div or 10mV/div...
At the input of your oscilloscope you can see maximun input voltage, but you need to see what is maximum voltage for your probe

[mike_mike]

Thanks for the reply.
What means "offset range bandwidth limit" ?
I found it in the manual and I took a screenshot:

The offset range bandwidth limit is the maximum voltage that can be applied at the input throught the 1x probe ?

[tggzzz]

Maximum input voltage is 300V no metter if you set scale for 10V/div or 10mV/div...
At the input of your oscilloscope you can see maximun input voltage, but you need to see what is maximum voltage for your probe

Not forgetting the max probe voltage as a function of signal frequency!

[tautech]

Thanks for the reply.
What means "offset range bandwidth limit" ?

They are two entirely different specs.

Offset Range. The amount the 0V of a channel can be offset (moved off screen) in order to display a waveform with a voltage offset.
Bandwidth Limit. Typically 20 MHz. Used to exclude the HF components of a signal and/or to clean up the waveform.

[mike_mike]

Thanks for the reply.
So the "offset range bandwidth limit" doesn't mean the maximum input voltage ? The maximum input voltage is 300V peak as it is mentioned in the manual ?

[tautech]

Thanks for the reply.
So the "offset range bandwidth limit" doesn't mean the maximum input voltage ?

Nothing to do with it at all.

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.

Study your probe pamphlet, don't push the limits of stated voltages and understand the frequency derating graph as tggzzz alluded to in his reply.

If you wish to extend the input voltage get a 100:1 or higher probe or for those with limited scope experience, a differential probe.

[Zero999]

Thanks for the reply.
What means "offset range bandwidth limit" ?
I found it in the manual and I took a screenshot:

The offset range bandwidth limit is the maximum voltage that can be applied at the input throught the 1x probe ?

I've not seen that before and I'm not certain. It looks like a maximum of +/-0.4V on settings equal or below 50mV/div, max +/-4V on settings between 100mV(10mV is probably an error) and 500mV/div, max of +/-40V, on settings from 1V/div to 5V/div and +/-300V on 10V/div.

[mike_mike]

Thanks for the reply.
I asked the question from the first post on another forum (before asking the question here) and some of the people from that forum said that if I will set de probe to 1x and the oscilloscope to 2mV/div (AC or DC coupling) and connect the probe to 200V peak, the oscilloscope will be damaged. Is that true ?
I am a beginner and this is my first digital scope so I am worried not to damage the scope when I work with it.

[Zero999]

Thanks for the reply.
I asked the question from the first post on another forum (before asking the question here) and the people from that forum said that if I will set de probe to 1x and the oscilloscope to 2mV/div and connect the probe to 200V peak, the oscilloscope will be damaged. Is that true ?
I am a beginner and this is my first digital scope so I am worried not to damage the scope when I work with it.

Yes, the specification indicates that, although hopefully, the input protection circuity should prevent any damage, although it's not a certainty.

[tautech]

Thanks for the reply.
I asked the question from the first post on another forum (before asking the question here) and the people from that forum said that if I will set de probe to 1x and the oscilloscope to 2mV/div and connect the probe to 200V peak, the oscilloscope will be damaged. Is that true ?

Maybe.
It's not standard practice to use probes set to 1:1, instead 10:1 is most often used.
In the channel menu set the input to the attenuation to match the probe then the OSD values will be correct.

Like any measurement device you can bust it if it's not set correctly so don't go anywhere near HV until you know exactly what you are doing.
At ~50V you can't get into too much trouble but for starters even stay a little lower until you are confident in usage. RTFM from front to back, 2 or 3 times, do simple tests to understand usage and become familiar with the controls.

As much as I hate it, Auto set is useful for scope newbies like you.

[mike_mike]

I read a part of the manual and I searched in the manual for some key words, but there is not mentioned the maximum voltage for the 2mV/div input.
If I will use the scope at a maximum voltage of 100V peak with the 1x probe and 2mV/div should be ok ? For example I am thinking that I will make a mistake and put the probe to 200V peak, with the 1x probe and 2mV/div. The scope will be damaged ?

[tautech]

I read a part of the manual and I searched in the manual for some key words, but there is not mentioned the maximum voltage for the 2mV/div input.
If I will use the scope at a maximum voltage of 100V peak with the 1x probe should be ok ?

For what good reason ?
Why even think about stressing the inputs of a scope with HV and 1:1 probes ? 

[mike_mike]

I am thinking that I will make a mistake..
For example I have a linear power supply and I want to measure ripple on 2mV/div with 1x probe and AC coupling, and the output of the power supply is 30Vdc.

[tautech]

I am thinking that I will make a mistake..
For example I have a linear power supply and I want to measure ripple on 2mV/div with 1x probe and AC coupling, and the output of the power supply is 30Vdc.

Then how you approach the measurement technique will minimize the chance of a mistake.

Who said you must use 2mV/div ?
Who said you must use 1:1 probe ?

Engage some little thought. Check first at a higher V/div setting then increase the sensitivity searching for the ripple. Never jump into a measurement at high sensitivity settings, never !!

[tggzzz]

I am thinking that I will make a mistake..
For example I have a linear power supply and I want to measure ripple on 2mV/div with 1x probe and AC coupling, and the output of the power supply is 30Vdc.

One easy way to make a mistake is to have a *1/*10 switchable probe. Sooner or later the switch will be in the wrong position.

Fortunately that is easy to avoid.

[glarsson]

Fortunately that is easy to avoid.

How? My standard probes are *10 but sometimes *1 would be nice. Have not found any *1 probes for sale! Hot glue in the switch doesn't solve all problems as the switch can become flaky.

[Zero999]

Fortunately that is easy to avoid.

How? My standard probes are *10 but sometimes *1 would be nice. Have not found any *1 probes for sale! Hot glue in the switch doesn't solve all problems as the switch can become flaky.

Get a x10 probe without a switch.

I read a part of the manual and I searched in the manual for some key words, but there is not mentioned the maximum voltage for the 2mV/div input.

Yes there is. It's in the screen shot you previously linked to and I explained it above. I repeat the maximum voltage rating is +/-0.4V on settings equal or below 50mV/div. Use a x10 probe if you want to use it on your 30V supply.

[glarsson]

Get a x10 probe without a switch.

How does that help?
I already have plenty of nice and expensive x10 probes without switches. What I don't have is a x1 probe without a switch.

[oldway]

I am thinking that I will make a mistake..
For example I have a linear power supply and I want to measure ripple on 2mV/div with 1x probe and AC coupling, and the output of the power supply is 30Vdc.

Why use an oscilloscope to measure the ripple on a linear power supply?

The ripple of a linear power supply is either 50Hz (60Hz) or 100Hz (120Hz), this can easily be measured with a multimeter on the AC range.
Some multimeters can also measure the frequency of the ripple.

With switching power supplies, it is better to use an oscilloscope because the frequency of the ripple is often too high for the multimeter.

[tggzzz]

Fortunately that is easy to avoid.

Have not found any *1 probes for sale!

Oh Good Grief.

https://www.digikey.se/products/en/test-and-measurement/test-leads-oscilloscope-probes/629?k=oscilloscope+probe&k=&pkeyword=oscilloscope+probe&pv331=270&FV=ffe00275&mnonly=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

That wasn't too difficult.

[GBowes]

I read a part of the manual and I searched in the manual for some key words, but there is not mentioned the maximum voltage for the 2mV/div input.

Yes there is. It's in the screen shot you previously linked to and I explained it above. I repeat the maximum voltage rating is +/-0.4V on settings equal or below 50mV/div. Use a x10 probe if you want to use it on your 30V supply.

Sorry, but I must suggest that this is not correct.
The Maximum input voltage to the BNC connectors on this scope is the 300V referenced previously.

Tautech had it correct about Offset Range yesterday so I am not sure how the question came back up.

The "Offset Range" has nothing to do with safe Maximum Voltage Inputs. It simply specifies how far the zero voltage reference point may be moved to try to get the trace on the screen.
The "bandwidth limit" is just the next line in a long list of specifications and has no bearing on the input voltage. In this case it is saying that this scope has a 20MHz Bandwidth Limit switch. When enabled, this will attenuate higher frequencies in the input signal.

The fact remains that some of the voltages in question can be dangerous and should be avoided until one has a complete understanding and familiarity with the operation and application of any measurement instruments.

Graham

Thanks for the reply.
What means "offset range bandwidth limit" ?
I found it in the manual and I took a screenshot:

The offset range bandwidth limit is the maximum voltage that can be applied at the input throught the 1x probe ?

I've not seen that before and I'm not certain. It looks like a maximum of +/-0.4V on settings equal or below 50mV/div, max +/-4V on settings between 100mV(10mV is probably an error) and 500mV/div, max of +/-40V, on settings from 1V/div to 5V/div and +/-300V on 10V/div.

[Zero999]

I read a part of the manual and I searched in the manual for some key words, but there is not mentioned the maximum voltage for the 2mV/div input.

Yes there is. It's in the screen shot you previously linked to and I explained it above. I repeat the maximum voltage rating is +/-0.4V on settings equal or below 50mV/div. Use a x10 probe if you want to use it on your 30V supply.

Sorry, but I must suggest that this is not correct.
The Maximum input voltage to the BNC connectors on this scope is the 300V referenced previously.

Tautech had it correct about Offset Range yesterday so I am not sure how the question came back up.

The "Offset Range" has nothing to do with safe Maximum Voltage Inputs. It simply specifies how far the zero voltage reference point may be moved to try to get the trace on the screen.
The "bandwidth limit" is just the next line in a long list of specifications and has no bearing on the input voltage. In this case it is saying that this scope has a 20MHz Bandwidth Limit switch. When enabled, this will attenuate higher frequencies in the input signal.

The fact remains that some of the voltages in question can be dangerous and should be avoided until one has a complete understanding and familiarity with the operation and application of any measurement instruments.

Graham

Thanks for the reply.
What means "offset range bandwidth limit" ?
I found it in the manual and I took a screenshot:

The offset range bandwidth limit is the maximum voltage that can be applied at the input throught the 1x probe ?

I've not seen that before and I'm not certain. It looks like a maximum of +/-0.4V on settings equal or below 50mV/div, max +/-4V on settings between 100mV(10mV is probably an error) and 500mV/div, max of +/-40V, on settings from 1V/div to 5V/div and +/-300V on 10V/div.

Thank you for your answer. To be honest, I wasn't sure about it when I posted it. I made more of a big deal about it, because I wanted someone to either confirm or correct it.

Yes, that makes much more sense. An instrument rated to 300V peak, is rated to that voltage on all settings.

[mike_mike]

Thanks for the replies.
I noticed a thing that I cannot explain: while the probe and the oscilloscope is set on 1x the noise from one power supply is about 5-6mV pp, while the probe and the oscilloscope is set on 10x, the noise from the same power supply (a LM317 power supply with PNP pass transistor) is about 50-60mV (see the images below, the first image with 1x probe and scope and the second with 10x probe and scope). Is that normal ?

[zvonex66x]

Yes, it's normal but you have changr probe from 1x to 10x but you didn't change probe in your oscilloscope settings

[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 ? 

[David Hess]

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 ?

You probably were not measuring noise from only the power supply.  At such low levels, a differential or coaxial connection should be made.  For a power supply, the bandwidth should also be limited because a majority of the noise from the power supply is at low frequencies.  Traditionally oscilloscope bandwidth is limited to 20MHz when making power supply noise measurements but lower would actually be better except when it is a switching power supply.

[mike_mike]

Thanks for the reply.
In the next image (the image shows the ripple at the output of an linear LM723 power supply) the frequency measured by the scope is 115.2Hz because of the noise ?

The value from the first image also fluctuates randomly, sometimes it is 100Hz, sometimes it is 300Hz, sometimes is about 1.5KHz. Is that normal ?
In the next image the ripple on the filter capacitor I think is clear and the frequency is about 100 Hz as I expected: https://imgur.com/a/e4kdI

[David Hess]

Regulators have a high but limited "line rejection" which allows some of the ripple at the input to appear at the output.  To see this, set the oscilloscope's acquisition mode to averaging to reduce the noise level and the triggering to line.

[mike_mike]

 Thanks for the reply.
In the country were I live the mains electricity is 230Vac. When I measure the mains voltage using an Unit UT52 multimeter, the multimeter measures about 247Vac.
It is safe to use the oscilloscope at this voltage (247Vac) ? In the oscilloscope manual it is wrote that it can be used up to maximum 240Vac ? Also in the manual it says "the power supply voltage should not fluctuate more than 10%"

[Dubbie]

Dave made a good video a few years back on the topic of measuring power supply noise and ripple. Worth a watch if you are new to this!

https://youtu.be/Edel3eduRj4

[mike_mike]

 I watched only a part from that video a few weeks ago.
I am still waiting for an answer for the question that I asked in my previous post.

[tautech]

I watched only a part from that video a few weeks ago.
I am still waiting for an answer for the question that I asked in my previous post.

DON'T probe mains with ordinary probes. Period.

The energy levels are too high to risk it. It's your choice but I tend to restrict myself to ~150V with 10x probes and anything higher brings out a 100x or 1000x probe.
With a modern DSO with good sensitivity such probe attenuation is no handicap.

[mike_mike]

I think I was not sufficiently clear when I wrote the first question.

My question is if I can power the oscilloscope from the mains (230Vac here in Europe) if the mains voltage is 247-250Vac, while in the manual is mentioned that the scope can be powered up to 240Vac ?
The value of the mains voltage (247Vac) was measured with an Uni-t UT52 digital multimeter.

[mike_mike]

When I was calibrating the probe, I saw that the calibration signal is having a little ”movement” on the screen. For example, I saw that the vertical lines of the signal are making some movement to the left and to the right as you can see from this video: https://www.youtube.com/watch?v=IOxCg90y3JI&feature=youtu.be

The settings on the scope are: 1V/div, 250uS/div

Is that movement of the vertical lines normal ?

[tautech]

I think I was not sufficiently clear when I wrote the first question.

My question is if I can power the oscilloscope from the mains (230Vac here in Europe) if the mains voltage is 247-250Vac, while in the manual is mentioned that the scope can be powered up to 240Vac ?
The value of the mains voltage (247Vac) was measured with an Uni-t UT52 digital multimeter.

Yes, it's safe to use it connected to your mains. All mains voltages worldwide have some variation and instrument design allows for it.

When I was calibrating the probe, I saw that the calibration signal is having a little ”movement” on the screen. For example, I saw that the vertical lines of the signal are making some movement to the left and to the right as you can see from this video: https://www.youtube.com/watch?v=IOxCg90y3JI&feature=youtu.be

The settings on the scope are: 1V/div, 250uS/div

Is that movement of the vertical lines normal ?

Normal.

[Damianos]

Additionally on what tautech says:
- the devices that are to be used on 220/230/240 Volt mains have a typical upper limit on 265VAC, that is the plus 10% of 240VAC. The lower limit, for proper operation, is around 198V.
- the horizontal "dancing" of the signal is just one pixel. Decreasing the time base, you can see that the line is not exactly vertical, so the instrument places the signal one time to one pixel and the other to the next one...

[mike_mike]

Hello,
I have a UTD2025CL DSO.
I was checking if there are oscillations on the output of a TL431 regulator and I got the attached screenshots.
It is normal to appear "multiple" wave forms on the same channel as in the image attached (MAP003 and MAP002) ?
The oscilloscope was set to AC coupling. The other settings can be read from the screenshots.

[vk6zgo]

Hello,
I have a UTD2025CL DSO.
I was checking if there are oscillations on the output of a TL431 regulator and I got the attached screenshots.
It is normal to appear "multiple" wave forms on the same channel as in the image attached (MAP003 and MAP002) ?
The oscilloscope was set to AC coupling. The other settings can be read from the screenshots.

Yes!
If you look at the display at 10ms/ div, you see effectively a 100Hz waveform, as would be expected from a linear supply operated from 50Hz Mains.
The "furry" stuff riding upon it is the high frequency stuff you see at shorter time/ div settings.

It is not unusual for a complex signal to look very different at widely different time/ div settings.

For instance, MAP002 is just MAP001 "zoomed in"

[radiolistener]

It is normal to appear "multiple" wave forms on the same channel as in the image attached (MAP003 and MAP002) ?

yes, it is normal. On first scan it has one waveform, on second scan it has another waveform, etc.

[mike_mike]

In the attached screenshot, the trace is a little bit lower than the mark on the screen for CH1. Why is this happening ? It is normal ? It has some relationship to the separation of the AC from DC signal ?
The signal source is the same TL431 power supply as mentioned above.

[mike_mike]

I have found that if I let the oscilloscope powered on for a few minutes, the offset between the trace and the CH1 mark is getting lower and lower. Is that normal ?

[Damianos]

Yes! All instruments have a "warm-up time", to become in the "normal conditions", where they are calibrated...
You can find that information in the specifications section of the manual.

[radiolistener]

Maximum input voltage is 300V no metter if you set scale for 10V/div or 10mV/div...

I suspect that if you put 300V 500 MHz, the input will be burned out like a match 

Some time ago, I asked Siglent support what is amplitude limit for high frequency for 1M input of their oscilloscope. I asked for 100 MHz frequency. They give me answer 40 Vpk. 

400 V is supported through 10x probe. 400 / 10 = 40 

I think 40 Vpk at 100 MHz is too much, I don't believe it can handle it with no damage. So, I don't want to test it   

[tggzzz]

Maximum input voltage is 300V no metter if you set scale for 10V/div or 10mV/div...

I suspect that if you put 300V 500 MHz, the input will be burned out like a match 

Some time ago, I asked Siglent support what is amplitude limit for high frequency for 1M input of their oscilloscope. I asked for 100 MHz frequency. They give me answer 40 Vpk. 

400 V is supported through 10x probe. 400 / 10 = 40 

I think 40 Vpk at 100 MHz is too much, I don't believe it can handle it with no damage. So, I don't want to test it   

Now look at the derating spec for the probe.

15pF at 100MHz is 100ohms. 400V into 100ohms means 4A is flowing