RIGOL DS 1052E measurements

Thread Starter

Doros

Joined Dec 17, 2013
137
Dear all hello,

I was using my oscilloscope, measuring the output of a power supply (switch mode), and since I am not familiar with oscilloscope measurements yet, I was changing the volts (vertical section) from 5V to 20V when the input was 9V.

The result was changing completely and for example the scope showed me in these two measurements different results.

At 5V /division it showed me a Vp-p (probably noise I am not sure of what it is) of 600mV, but at 20V/division a 2,4V Vp-p showed up.

The same happens with a 9V battery, and every measurement.

So when I make a measurement the where I should put the V/division? very near to what I measure? Propably I am missing something here.

Thank you very much for your help
 

Attachments

MrAl

Joined Jun 17, 2014
7,891
Hi,

Normally you set the vertical to a range that i higher than what you intend to measure. If you font know, set to a high range then back down once you start getting a reading.
 

Wuerstchenhund

Joined Aug 31, 2017
189
A few things:

- Your scope has an 8bit ADC, i.e. it can only "see" 256 voltage steps. That limits the resolution of any measurement.

- These 256 steps are over the full screen height, so to make use of the full dynamic range of the ADC the scope should be setup so that it shows the signal under test as large as possible but without any clipping. Now if your signal under test is only say 1 division from the null line then you're wasting the majority of dynamic range and might end up using only three bits (ie. 9 steps), which dramatically reduces voltage resolution.

- Scopes like your Rigol make measurements not from the sampled data but from the screen buffer, which on this scope uses a very low resolution. This will impact your measurement resolution/accuracy even more, especially if the signal under test is using just a small part of the vertical screen estate.
 

Thread Starter

Doros

Joined Dec 17, 2013
137
Many thanks Wuerstcheh und and MrAl.

MrAl's help is very close to my level.

Wuerstgheh und, my simple knowledge of oscilloscopes, analogue and digital, is that briefly speaking, analogue oscilloscopes show you real time signal fluctuation / time, and digital, gathers analogue signals, convert them to digital and show you the variation of a signal / time (probably after some μSec this happened).

In my case is it possible to have a descent measurement? If I understood well I will try to use the whole screen, but without having my signal going beyond it. (Not having any clipping)

And in order to find out how reliable my scope is, I have to use either the embedded square wave signal, or a signal I know very well its characteristics. (I do not have a signal generator)

thank you for your help
 

Wuerstchenhund

Joined Aug 31, 2017
189
Wuerstgheh und, my simple knowledge of oscilloscopes, analogue and digital, is that briefly speaking, analogue oscilloscopes show you real time signal fluctuation / time, and digital, gathers analogue signals, convert them to digital and show you the variation of a signal / time (probably after some μSec this happened).
Yes and no. Even an analog scope isn't instantaneous in the true sense, as there will be some delay until an event is shown on the screen, and albeit the delay is small it can very well mean that the event is over by the time its visible on the screen. A digital scope which has to sample the signal and process the digital data usually takes a bit longer than the analog scope until a event is visible on the screen, however for scope measurements this is irrelevant as the scope time axis does not show realtime but simply the time since the trigger event.

In my case is it possible to have a descent measurement? If I understood well I will try to use the whole screen, but without having my signal going beyond it. (Not having any clipping)
Just try to make it as big as possible without clipping. Many digital scopes not only offer fixed stepped vertical settings but also variable settings so you can maximize the signal as much as possible. If your scope doesn't have them then just turn up the vertical setting until it clips and then one back so you get an unclipped signal.

And in order to find out how reliable my scope is, I have to use either the embedded square wave signal, or a signal I know very well its characteristics. (I do not have a signal generator)
Well, the screenshots suggest your scope is a pretty old Rigol DS1000 Series scope (such low res screens haven't ben used in scopes for years now), and if I remember right its firmware had various bugs which may or may not have been fixed so I'd check that you got the latest version installed.

But yes, in general you want a signal of known specifics that is within your scope's frequency range and time resolution (sample rate) if you want to check out your scope's measurement reliability.
 
Last edited:

Thread Starter

Doros

Joined Dec 17, 2013
137
Thank you very much Wuerstcheh und for your input and valuable information,

I begin to understand now the "secrets" of scope measurements. Playing with my RIGOL, I will discover most of them.

A last question, concerning measurements:

If you see the measurements of this pure DC Volt, you observe a Vp-p of some mVs. It shouldn't be there. Even measurement of the battery. Is it a kind of external noise?

thanks again
 

Wuerstchenhund

Joined Aug 31, 2017
189
If you see the measurements of this pure DC Volt, you observe a Vp-p of some mVs. It shouldn't be there. Even measurement of the battery. Is it a kind of external noise?
The ripple you see is indeed some noise, probably introduced by the probe's GND wire which tends to act like an antenna and catch environmental noise. There are ways to compensate for that (i.e. better probing, use of AVERAGING function if available) but at the end of the day an oscilloscope isn't the right tool to measure D.C. voltages. A decent DMM should give you much more precise results.
 

Thread Starter

Doros

Joined Dec 17, 2013
137
Thank you Wuerstcheh und,

I used the DC V, to explore my scope. I agree it doesn't make sense use it for DC measurements

you helped me a lot
 
Top