What are the factors that affect the waveform refresh rate of an oscilloscope?
Sampling time and dead time
The waveform refresh rate is the reciprocal of Tacq (sampling time) and Tdeat (dead time). The sampling time is determined by the sampling pane of the oscilloscope screen. Multiply the horizontal time base gear by the number of horizontal grids. When the horizontal time base is determined, The sampling time will be fixed.
The dead time is determined by the processing capability of the oscilloscope. When the oscilloscope has insufficient data processing capabilities, it will not be able to process the collected big data in time, the dead time will become longer, and the refresh rate will decrease; when the oscilloscope When the data processing capability is strong, the dead time will be shortened and the corresponding refresh rate will be high. Therefore, dead time is an important factor affecting the refresh rate.
Trigger holdoff time
Increasing the trigger holdoff time is equivalent to increasing the dead time in disguise, because during the holdoff period, the trigger circuit is closed and the trigger function is suspended. Even if there is a signal waveform that meets the trigger conditions, the oscilloscope will not trigger, so it will also affect the refresh rate. . But the trigger holdoff time does not refer to the dead time.
When triggering on a large-period repetitive waveform, there are many waveform points in the waveform that meet the triggering conditions, causing the trigger waveform to be unstable. In order to obtain a stable triggering waveform, we can set the trigger holdoff time so that the waveform is at the same time every time. A point triggers and the trigger waveform is displayed stably.
How to calculate dead time?
When capturing an abnormal pulse with a pulse width between 40ns and 60ns, the appropriate horizontal time base gear can be set to 50ns/division. At this time, the ZDS2022 oscilloscope has a waveform refresh rate of 330,000 frames/second, which means each trigger sampling The total capture time occupied is T = 1s/330KHz = 3.03us, then the effective sampling time is 50ns/divX14 (ZDS2022 oscilloscope has 14 divisions in the horizontal direction) = 700ns. Then the dead time percentage is (3030-700)/3030=76.89%.
Capturing the same abnormal pulse, at the same time base gear, if the T oscilloscope has a refresh rate of 50K frames/second, it means that the total time occupied by each trigger sampling is, T=1S/50KHz=20us, effective The sampling time is 50ns/div
The longer the dead time, the lower the probability of capturing occasional signals. When a small probability abnormal waveform appears in the dead time, the oscilloscope will not capture the exception, which will have a great impact on signal debugging.
