We are continuing in our quest to evaluate oscilloscope options and finding some really quirky bugs.
On my desk now is a Tek MDO34, 200MHz bandwidth, 2.5GSa/s ADC with the 3GHz RF input.
The behaviour (I am not sure it is a bug) manifests as such (there are almost certainly other ways to trigger it, but this one is consistent):
- Set scope to normal trigger with an input signal (noisy signals work well, as they show many graduations on the DPO)
- Set the trigger up so no events are captured, and run the scope. No waveform appears.
- Force a trigger using 'Force' button. Waveform appears. Note that the waveform appears to have random and continuous noise.
- Disconnect any input signal for further reassurance that acquisition is not actually occurring.
- Note that despite no acquisition occuring, the scope seems to emulate the appearance of waveform update with the noise added to the waveform. However, if you adjust the timebase or V/div scale, press Run/Stop or do anything to the acquisition, the animation stops and won't restart until the acquisition is re-run.
As behaviours go, this is odd. My best guess is that Tek apply this noise to the waveform to make the update rate appear higher or to implement the dynamic phosphoring (perhaps related to persistence features.) However, it seems to be left on whenever a channel is on, which can mislead the user into seeing a continuous update when none is present.
Tested on firmware v1.6.0 (2019-08-08)
Edit: This only seems to occur on auto persistence. So it seems to be related to persistence remaining on after an acquisition. In the mode without persistence the bug/behaviour is not present.
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