ADP3250 Scope Reading With No Probes Connected

[janpi]

I have recently purchased a new ADP3250. I have noticed that if no probes/inputs are connected the scope still shows 3 mV peak to peak reading of what looks as a random noise. If I connect supplied probe and shorten its ends the reading jumps to approximately 20 mV. Screen shot with shorten probe leads is attached.

Is this normal? Am I doing anything wrong? It seems high to me as I cannot measure any signal below 20 mV noise level.

Thank you for any help.

[attila]

Hi @janpi

It looks like you have a nearby radiation source of about 16 4.1 MHz.
With shorted probe end I see about 5mV pk2pk noise, C3 of ADP3450 is in location C1 of ADP3250.

(For nicer UI on MacOS and Linux, recommend to use the Settings/Options/Style: Fusion)

[janpi]

Thank you for your quick feedback and UI tip Attila.

I had the similar thought so I took the ADP3250 and the battery powered laptop (no charger connected only the ADP3250) to a room with no plugged electronic/electrical devices and unfortunately saw the same output. The laptop MacBook Air M2.

Any thoughts what should I try to troubleshoot?

[attila]

Hi @janpi

I don't know what could be the cause of this.
You could use Filter channel to filter hf components and/or various averaging options in the application.

 

Edit: To measure the input 'internal' noise a (50R) terminator or a very short wire shorting the BNC input should be used.
Additional wire will absorb more radiation. For instance a probe ground loop can be used to locate the source/orientation of the radiation:

[janpi]

Thank you for another tip Attila! There is so much to learn in WaveForms, btw it is a great app.

I made some progress today. I have used different design probe and with shorted end I am getting noise just < 3 mV pk2pk. See screenshot.

Can you please let me know what are you getting on C3 on your ADP3450 with no probes connected?

[JColvin]

Hi @janpi,

I'm not Attila of course, but this is what I get for Channel 3 with no probe or shorting:

The offset appears to be different than yours, but is otherwise of a similar magnitude.

Thanks,
JColvin

[attila]

Hi @janpi

On 10/31/2023 at 11:38 AM, attila said:

Edit: To measure the input 'internal' noise a (50R) terminator or a very short wire shorting the BNC input should be used.
Additional wire will absorb more radiation.

A floating high impedance input is not a good metric, it can pick up random radiation from anywhere.

[janpi]

Thank you for your feedback and guidance Gentlemen!