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buy a better oscilloscope than the Siglent SDS1104X-E
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uargo:

--- Quote from: Martin72 on August 18, 2023, 10:02:36 pm ---
--- Quote --- better even than the $4,600 12-bit 350Mhz SDS2354X HD which has 70uVrms
--- End quote ---

65µVrms, look at the datasheet.
And: Noise rises more or less with the bandwith.
Plus: The difference between 56µVrms and 65µVrms is....nothing.
Plus, the second: You already have a SDS1104X-E, so you can measure it in real and now. ;)
At the moment I let the SDS1104X-E warm up for it...

--- End quote ---

I put a link to the siglent document that supports what I say, can you do the same, please
Martin72:
LOL...OK, look at the pic below.


--- Quote ---Can repeat it with the wanted parameter.
--- End quote ---

All channels, history mode, 20Mhz bw limit, picking the lowest value.

(damn...500µV/div. ....)
rf-loop:

--- Quote from: Martin72 on August 19, 2023, 02:24:10 pm ---
Interesting.
How can I make sure that not only the screendata will be used for the values ? The history record ?


--- End quote ---

How you can be sure. Very Simply. Just believe what we tell about it. (but do not believe everyone --- you know....)

But if you do not trust, you can also easy evaluate it. 
 

You can somehow test if it use decimation for display is using example slow timebases and narrow  pulses. If it decimate before display there start missing some these pulses. Not happen with Siglent. But one vertical column can have many of these pulses overlaid on screen (example if burst include many pulses but whole burst is only one display pixel width. (all pulses overlayed in this column)).  But still measurement can see separate pulses. 


Some oscilloscope measure using screen mapped data and then  there is max resolution same as screen resolution.
Some oscilloscopes may use this screen (mapped) data for measure.
Some scopes may use some other kind of intermediate buffer for measurements. More resolution than display resolution but less than is in sample buffer (depending time base etc).
There is also some older Siglent models what use intermediate buffer for measurements (example SDS1000X models because there is not brute force for handle full resolution full data length measurements)

This SDS1104/1204X-E use full sample buffer for measurements (just this memory length what display info screen tell about current memory length).

I think if you do some simple tests it tell lot of about this.

Idea is just that input signal have more time domain events than  than display resolution is. You can easy find many kind of signals for test it.
Here one example...  no need just this... 
Simplest is 10MHz sine and scope 1ms/div and then measurements about +width, interval etc etc... scopes what use display buffer fails here totally.

Set 1ms/div.
Produce signal what have 50ns width pulses and pulses period 1.001us (1001ns) and risetime example 15ns
Set measure for Period  and +Width and risetime.

If oscilloscope use screen buffer for measurement... All these measurements fails totally.

If horizontal resolution is example 700 pixel and 14 div (as is in SDS1000X-E models)
If 1ms/div, then 1 div pixel resolution is 20us. (time axis 50 pixel/div)   

But in this example measurement display pulse width around 50ns and period around 1001ns and also risetime based to 1ns resolution (because sampling interval is 1ns and because it use full acquistion resolution.

Ok do it use also really full length of data. Yes. You can easy test it... make signal so that nearly start of sample buffer is one pulse and nearly end of buffer next pulse (example 13ms interval, 50ns pulses. Set trigger half div after display left border. Yes you get 13us interval so lenght used for measurement is least this , you can see next pulse half div before right border and as you can see resolution for interval is 1ns.

Try with Rigol 1000Z. Also you can try with some Megazoom Keysight.  (no need test, I can tell situation is just "game over")

But one note. Example in this case. There is not Interpolation between true sample points in this case. So resolution is now sample interval. 

Long time ago here in forum was some very long thread about this measurement resolution with different oscilloscopes and also something about testing it. In this thread there is lot of data and information.
Fast searching I didn't find it.

Martin72:
Very interesting things, I need to read this in peace and find out more.
It's like a rabbit hole... 8)

Actually, I wanted to repeat the measurements with 1mV/div. but I don't feel like it today, especially since the offset from the scope keeps "running away" from me.
At some point, that's no longer any fun. ;)
But it's not mine, my HD is very easy to care for.
uargo:

--- Quote from: Martin72 on August 19, 2023, 04:14:06 pm ---LOL...OK, look at the pic below.


--- Quote ---Can repeat it with the wanted parameter.
--- End quote ---

All channels, history mode, 20Mhz bw limit, picking the lowest value.

(damn...500µV/div. ....)

--- End quote ---

the capture that you have put is at 50 ohm, of the SDS2104X HD model, THAT DATA OF THE SDS1104X-E does not exist published by Siglent. If you say that empirically it is that, then it will be, measuring the noise gives me unstable readings and strange things at those levels
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