Rigol DS1054Z odd waveform when I touch the probe tip

[Farid]

Hi guys, I have recently bought a Rigol DS1054Z and I have used the famous "DSER" to unlock all features and updated the firmware to the latest.

Currently I don't have much time to play with all of the features but recently I found a -glitch (maybe)  - and wanted to know whether my scope is bad or this behavior can somehow be explained?

The problem is when I touch the tip of the probe with my finger as the probe is connected to nothing I get a little jitter/noise on the flat signal line which is normal, but as I increase the time base the amplitude of the noise increases and it takes form as a 50Hz sinusoidal waveform. I have attached the picture from scope. Will be happy if anybody can explain me what's wrong.



 

[jpanhalt]

That's normal.   Your body is an antenna for you mains power.  Presumably it is at 50 Hz.

[Farid]

That's normal.   Your body is an antenna for you mains power.  Presumably it is at 50 Hz.

Thanks for the answer, Yes the mains freq is 50 Hz and also the wiring of the building I use this scope is old and the mains wiring only consists of active and neutral without Earth wire. but why 92Vp-p. 

[jpanhalt]

You are a good antenna and the impedance of the scope is high.   Put a resistor from scope tip to ground, say 20k, and see what you read.

Without a ground, your scope is also "floating."  There are both advantages and disadvantages to that and numerous discussions about it on various forums.  Some people run their scopes from a transformer to ensure it is not attached to the supply ground.

Is your neutral grounded at the supply to the building, as it is in the US, or is it separate all the way back to the supplier?

[David Hess]

The problem is when I touch the tip of the probe with my finger as the probe is connected to nothing I get a little jitter/noise on the flat signal line which is normal, but as I increase the time base the amplitude of the noise increases and it takes form as a 50Hz sinusoidal waveform. I have attached the picture from scope. Will be happy if anybody can explain me what's wrong.

Would need to see the pictures from the oscilloscope when the timebase is decreased and the noise is lower.  The picture you posted looked completely normal.

I am not sure if "increasing" the timebase means faster or slower but at faster timebase speeds, the low frequency content of the signal is cutoff so the noise is lower.  A triggered 50 Hz signal at 10us/div looks like a sloped line.

[Farid]

You are a good antenna and the impedance of the scope is high.   Put a resistor from scope tip to ground, say 20k, and see what you read.
Without a ground, your scope is also "floating."  There are both advantages and disadvantages to that and numerous discussions about it on various forums.  Some people run their scopes from a transformer to ensure it is not attached to the supply ground.
Is your neutral grounded at the supply to the building, as it is in the US, or is it separate all the way back to the supplier?

I'm glad that I'm not at least a bad antenna . I put the resistor and the waveform is gone you can see the attached picture.
As regarding the grounding, the wire coming from Utility Pole to the building it is only active and neutral, but there is a thick wire going from top of pole to the ground, so I think it is somehow grounded. But I'm not sure.

Would need to see the pictures from the oscilloscope when the timebase is decreased and the noise is lower.  The picture you posted looked completely normal.
I am not sure if "increasing" the timebase means faster or slower but at faster timebase speeds, the low frequency content of the signal is cutoff so the noise is lower.  A triggered 50 Hz signal at 10us/div looks like a sloped line.

By increasing, I mean increasing the value of Time/Div or somehow slowing the scope, I have attached the pictures.

Anyway thanks for the answers and I really appreciate the time and effort. To be honest I have used analog scopes before but didn't have such an issue. It's making me crazy.
 

[David Hess]

Anyway thanks for the answers and I really appreciate the time and effort. To be honest I have used analog scopes before but didn't have such an issue.  It's making me crazy.

Your new photographs show what I described.

An analog oscilloscope should behave in exactly the same way.

[hermit]

Mod.  Please merge these two threads!

https://www.eevblog.com/forum/suggestions/debunk-teardown-suggestion-scientology-e-meter/?topicseen