Purchased our first Picoscope this week. We bought a 2204A to do some control loop measurements.
I am seeing periodic bursts of noise on both channels, even with nothing connected to the inputs. The bursts appears at 1.0-1.2 second intervals, are about 50-100ms long, and the content within the bursts is about 400Hz, from what I can tell.
Please see the attached images.
For the first 1.5-2 minutes after the Picoscope is plugged in, and detected by Picoscope 6, there is no noise! If I quickly un-plug and re-plug in the scope, the noise magically vanishes, and then shows up again after 1.5-2 minutes. Very peculiar to me.
I've tried the following:
1. Tested on desktop PC plugged into AC mains, then tried on battery powered laptop
2. Moved the laptop setup to the opposite side of the building
3. Turned off WiFi on the laptop
4. Enabled/disabled the waveform generator
5. Disconnected all USB devices from both computers
6. Disconnected all scope probes and BNC cables from Picoscope
Thanks for replying. I've already tried with my phone powered down. The laptop does not have any sort of GSM/CDMA card. I've also already tried with WiFi switched off. I will try to short the inputs...I imagine the noise will go away.
I put a benchtop scope across both inputs. The noise is really there, at the BNC connectors.
The reason I don't think it's from anything near-field is because *the bursts only start after a 1.5-2 minute delay after plugging in the scope to PC USB*. This happens after every time I plug it in. Once the noise is present, if I quickly unplug and re-plug in the USB connector, once the scope re-initializes in Picoscope 6, the noise goes away.If the issue was related to radiated pickup, the noise would still be there once the scope was re-initialized, in my opinion.
I'm not exactly sure what you mean. I only took a screenshot once the noise bursts started to appear. For about 2 minutes, the trace was flat at 0V. For slow time-base like 1sec/div, the trigger is just rolling.
We have 5 other bench top scopes without any noise sensitivity issues, all in the same workspace. Granted, they are not connected to PCs. In my experience, with no probes attached, pickup should not be that severe.
I took the laptop and Picoscope into our fully shielded EMI test chamber. The noise is still there. The laptop has all wireless communications turned off. I left my phone outside the chamber. As I noted, the issue is instantly reset once I disconnect the Picoscope USB cable and plug it back in. If it was external noise, I do not see how reconnecting the USB cable would be related at all.
I opened a support case. Xujie recommended to try a different USB cable. (Seems like an "obvious" thing to do, but I had not done it.)
The issue is gone when using any other USB A-to-B cable, other than the blue one shipped with the unit. Very strange as I have no idea what kind of internal fault might be responsible for that. Something intermittent? But then why would it be periodic? I can't worry about it too much, but so far, everything is okay with a new cable.
Maybe a interference capacitor : cable not well done, or contact problem. This could explane the time delay and the periodic aspect...
Connections could be very tricky... and USB is not only a numeric bus, you also have CC in it.