Test and Measurement Forum

Picoscope has 52kHz noise internally?

Post any questions you may have about our current range of oscilloscopes

Picoscope has 52kHz noise internally?

Postby angelsix » Sat Jan 02, 2010 10:18 am

I'm trying to use the 2205 scope to see a problem on my ultrasonic driver circuit that for some reason isn't working. However I have spent weeks trying to figure out why my scopes are showing 52kHz noise coming out of the amplified output of the amp on my board.

I have finally pinned it down today by shear luck, and it turns out its absolutely nothing to do with my board, and it was just the fact that my amp was increasing the noise enough to make it visible. The noise is in fact coming from the scope itself :evil:

Can someone try this and confirm it or let me know how to solve it. Connect your Pico to the PC, open up software, set collection time to 5ms, divs to +-100mV and no triggers. Now without a probe connected, you can't see much. Put your hands around the Picoscope box or connect a probe... notice a 13mV P-to-P 52kHz noise.

Problem... when I connect this to my circuit the noise is showing up and getting in the way of the critical readings I need at the low mV levels (the entire reason I brought this scope). Any ideas?
angelsix
 

Re: Picoscope has 52kHz noise internally?

Postby alan » Sun Jan 03, 2010 3:25 pm

Hi,

I would be suprised if the noise was coming from the scope itself. From memory there is nothing that is switching inside the scope at that frequency. Its more likely that the scope is picking up some electrical noise from nearby - perhaps the circuit you are testing or the PC the scope is connected to.

Do you have any way of terminating / shorting the scope inputs? With the scope input shorted hopefully the noise will vanish. As with any scope any wire / cable / scope probe connected to the input will pick up nearby signals unless its perfectly screened.

If you dont have an easy way of shorting the input at the BNC short the scope probe. If the PC is a laptop try running it on batteries to see if that reduces the noise. If you are using a CRT monitor try moving the scope and scope probe away from the monitor.

It might be easier to find the source of the noise if you use the spectrum analyser view rather than the scope view.

Regards
Alan
alan
Site Admin
Site Admin
 
Posts: 171
Joined: Thu May 25, 2006 8:02 am

Re: Picoscope has 52kHz noise internally?

Postby BrianK » Fri Jan 08, 2010 4:14 pm

What Alan said, along with nearby CFL desk lamps and even flat-panel screens.

Seen those, been bitten by those... :oops:
To err is human; to moo, bovine.
BrianK
Newbie
 
Posts: 0
Joined: Fri Jan 08, 2010 3:57 pm

Re: Picoscope has 52kHz noise internally?

Postby alan » Fri Jan 08, 2010 4:24 pm

Just to clariify - scopes themselves should not pickup noise from CFL lamps / PC monitors etc. Thats what the internal screening is for.

The cables you plug into the scope and the circuits you are measuring may well pick up noise which the scope will then display. The scope is only doing its job - displaying signals fed into the BNC input.

Alan
alan
Site Admin
Site Admin
 
Posts: 171
Joined: Thu May 25, 2006 8:02 am

Re: Picoscope has 52kHz noise internally?

Postby BrianK » Tue Jan 12, 2010 11:01 pm

Apologies; I should have made it clearer that the pickup I experienced was entirely due to external cables/circuitry, and not the Picoscope itself.
To err is human; to moo, bovine.
BrianK
Newbie
 
Posts: 0
Joined: Fri Jan 08, 2010 3:57 pm

Re: Picoscope has 52kHz noise internally?

Postby angelsix » Wed Feb 03, 2010 9:26 pm

Just a quick update on this. I have still not found the source of the noise but it definately 1 of 2 things. From the scope itself, or being picked up by the scope.

I have tried running the scope with nothing connected to it (no probes only the USB cable to power it) and go to the highest resoltion and the noise is still there. I worked with my TV off, laptop screen off, lights off and scope moved a meter away from it and it faded about 60% by moving it away from the laptop, but was still present.

The reason this is such a problem is because for use I am probing an amplifier circuit input and output that amplifies the input 7,500x, and so the minor noise coming from the scope that has a probe on the input is coming out of the output end and making my scopes very hard to see anything useful. I experience around 800mV of this 52kHz noise still and if I find a sweet spot by moving everything around I can get this noise to drop right down to about 50mV at times, but it is still bugging me to where it is coming from any why.
angelsix
Newbie
 
Posts: 0
Joined: Wed Feb 03, 2010 9:15 pm

Re: Picoscope has 52kHz noise internally?

Postby BrianK » Fri Feb 05, 2010 5:07 pm

angelsix wrote:I have tried running the scope with nothing connected to it (no probes only the USB cable to power it) and go to the highest resoltion and the noise is still there.
But leaving the input open circuit practically guarantees that noise will be picked up! :shock:
What happens if you have the probes connected but shorted?
it faded about 60% by moving it away from the laptop, but was still present.
It appears that the noise is coming from your laptop.
Difficult to see it being anything else, since the noise level reduces as you move the scope away from it.
To err is human; to moo, bovine.
BrianK
Newbie
 
Posts: 0
Joined: Fri Jan 08, 2010 3:57 pm


Return to USB PC Oscilloscopes

Who is online

Users browsing this forum: No registered users and 0 guests