Electronics > Beginners
oscilloscope auto trigger explained
vk6zgo:
--- Quote from: Tom45 on October 08, 2018, 01:57:59 pm ---
--- Quote from: vk6zgo on October 08, 2018, 12:29:12 pm ---Thanks, David, it seems like I was incorrect.
The manual is not at all up to the standard of Tektronix's classic analog instruments.
I always felt that both the UI & the documentation on these early DSOs was like we used to say about Polaroid cameras.
"As if they had never seen a camera (or in this case an Oscilloscope), & were basing their design on a description sent in a badly mutilated FAX."
--- End quote ---
The manual is actually quite clear. I downloaded it and looked at the table of contents for Trigger Controls and was referred to page 3-54. Then went to 3-54 and 2 pages later on 3-56 is a chart and accompanying text describing auto mode. Using the manual, Auto trigger mode is easy to find.
As another person that grew up with analog scopes, I submit that the actual problem is the difference between analog scopes with knobs and buttons for everything vs. digital with many things hidden away in menus. Those of us used to analog scope front panel controls can find Auto mode right away. With new digital scopes we need to go to the manual, or poke around in menus until we find it.
The 465 and 2246 front panel examples are obvious but the THS720A menu structure isn't.
--- End quote ---
I still question the logic of putting information on an often used function 136 pages into the manual.
With the analog Tek Oscilloscopes, such things were in the first few pages.
This is symptomatic of what seemed to have been a radical change in culture between the last generation of analogs & the first generations of DSOs, in both Textronix & HP.
Representatives of both companies who visited my old work, touting the advantages of the (then) new DSOs, would "read from their script", expecting this to be greeted with "oohs! & aahs!".
Once that meagre source of information was exhausted, they seemed to have no answers to issues brought up by people who used 'scopes every day.
Things which were of great importance to us were treated as "nitpicking" by "technological dinosaurs".
SilverSolder:
--- Quote from: vk6zgo on October 09, 2018, 04:02:41 am ---
With the analog Tek Oscilloscopes, such things were in the first few pages.
--- End quote ---
Older instruments (not just scopes) are far more "task focused"... you can usually get an older device up and running, including remote operation via IEE488 using simple text commands - all within a few hours after unboxing it, even if you've never seen or used one before.
The manuals for them are usually task focused as well - introduce the instrument, explain its accuracy and limitations, and show how to use it in a basic way, all within the first few pages.
Newer instruments, in contrast, have a thick layer of software on top of their basic sensing features that takes time to learn, and sometimes ends up getting in the way if you want to try something outside the design parameters. Remote operation usually requires installing software on your PC which also has to be learned before you can do much with it (forget about simple ASCII commands).
Consequently, the manuals have to go through an enormous amount of "preparatory work" before you get to use the instrument, even in a basic way.
Tom45:
I've attached the scope's table of contents.
After the getting started section that a few trivial and probably obvious preliminaries and the Functional Overview ditto, it goes on for many pages of how to do a number of possible tasks (General Purpose Application Examples). Note the 7 page Understanding the front panel section. Because most digital scope features aren't found on the front panel, and especially for a handheld digital scope with a tiny "front panel", this front panel section just isn't going to get into the kind of detail that analog scope manuals covered in the equivalent section.
Finally a Reference Section deals with all features including those that aren't found on the front panel.
I got to the auto trigger information by looking at the table of contents where I found the trigger controls section. Just as easily someone could have looked in the index where auto mode triggering is shown to be on page 3-56.
The auto trigger info is easy to find using either the table of contents or the index. That information could easily be missed doing a linear search through the 230 page manual.
Rohde_TestWalker:
Hey stern0m1, here's how the manual explains auto and normal triggering:
• Auto: in this trigger mode, the oscilloscope will force a trigger if the specified trigger condition is not found.
• Normal: in this trigger mode, the oscilloscope only triggers when the specified trigger condition is found.
Of course, which mode you should use depends on the type of signal you're trying to measure. If you're trying to measure a DC signal then selecting auto trigger mode will always display the signal. If you're trying to measure an AC signal, though, then you probably want to select normal trigger mode and set the trigger level and slope. Adjusting these levels will give you a stable display, which you can then use to make your measurements.
One of the cool features of modern digital oscilloscopes is the AUTOSET feature. When you press the AUTOSET button on the scope, it will analyze the signal, and adjusts the horizontal, vertical, and trigger settings to display a stable waveform. You can then make your measurement. Hope this helps and you're up and running quickly. Rohde_TestWalker
alsetalokin4017:
Autoset may be a cool feature of modern DSOs but it is a crutch, and can really mess your scoposcopy mind up if you depend on it too much. Some scopes even come with a way to _disable_ the Autoset feature so that student technicians don't learn to rely on it, but rather learn how to set up the scope themselves for their desired measurements. The Rigol DS1054z is one such scope which allows disabling the Autoset feature. (in Utility>Auto Options). Careful, if you disable it here in this menu you will have to use the SCPI command over LAN or USB to re-enable it.
Also, the Auto trigger mode is clearly accessible on the front panel of the DS1054z, simply by pressing the MODE button in the Trigger section of the front panel on the right side center. The current Trigger Mode is indicated both by an LED above the button and also in the top left corner of the screen display. Here, the "AUTO" word flashes when the scope is "free running", and changes to "T'D" when the scope senses an external signal that meets the Trigger parameters set in the Trigger menu. The default is rising edge, voltage set with knob. Since a DC voltage won't have a rising edge, it won't satisfy the trigger condition and the scope will continue to flash "AUTO" at top left, and the trace level will show the voltage.
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