oscilloscope trigger occurance (regarding trigger level) - Page 1
Forum section: electronics / projects

author: SArepairman
author_rank: Frequent Contributor
timestamp: February 22, 2014, 03:06:49 am
content: So I noticed with certain waveforms if you adjust the trigger level in the middle of the wave you just get some nasty mess, but if you move the trigger level to near the peaks of the waveform you are trying to display it stabilizes... I believe that dave jones said that this kind of triggering is actually giving you a false version of the wave form, and its "cheating", but I cannot recall this video

author: I_may_be_drunk_right_now
author_rank: Contributor
timestamp: February 22, 2014, 03:20:20 am
content: I have no idea what you're talking about but it sounds like you need to find the holdoff control.You really need to tell us more about what it is you're looking at. What scope? Analog? Digital? What waveform? Frequency? Voltage? What probe? What middle? What's a "mess"?The only time I recall Dave talking about "cheating" is wrt undersampling, where I totally disagree with his opinion, but such is life.

author: SArepairman
author_rank: Frequent Contributor
timestamp: February 22, 2014, 03:35:37 am
content: Quote from: I_may_be_drunk_right_now on February 22, 2014, 03:20:20 amwell its something I noticed with all types of waveforms on my rigol 1052e.If you get a messy noisy waveform (such as amplifying a low level signal where you know the input frequency). Just looking at the waveform it looks like a mess. However if you carefully adjust the trigger level (just go up by steps of 1) eventually you can get a much more cleaner looking waveform, so you can actually tell the frequency of it.In the current case I am looking at a heavily amplified AC coupled audio signal. (function generator> attenuator> amplifier (gain 187,000 on a breadboard, multiple op amps) > scope). I noticed it before though with other waveforms in the past though.

author: w2aew
author_rank: Super Contributor
timestamp: February 22, 2014, 04:39:04 am
content: This is most often caused by noise on the signal. When the scope rearms the trigger circuit, it looks for the first trigger event (edge, etc.) that it sees. If there is noise on a signal, the first tiny edge that crosses the trigger level will cause a triggered acquisition. Sometimes this little noise edge it sees will be at a different point in time than your desired point.I have a video where I show a waveform that looks like an unstable trigger, but turns out to be a small oscillation on the waveform that causes the scope to trigger on multiple edges. I traced the problem down to a problem in the power supply circuit.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 22, 2014, 05:30:49 am
content: The trigger circuit can start at any intersection of the waveform and the trigger level. If the waveform crosses multiple times, you may get an ambiguous display. Adjust holdoff, trigger level or bandwidth as needed.If you can't see the extra crossings on the waveform, try Peak Detect mode. This won't show the extra crossings, but it will make it obvious that more is going on, and where along the waveform.Tim