Chinese scopes annoyingly expand around center instead of trigger?! - Page 1
Forum section: electronics / testgear

author: appsman
author_rank: Contributor
timestamp: May 07, 2020, 12:42:52 am
content: Maybe I'm missing something, but it seems that on a Rigol 'scope, if you move the trigger to a point a division or two inside the left edge of the screen (as I often prefer to do), and then change the timebase, the display expands around the center of the screen and the trigger point flies off the screen. The trigger point only stays still if it's in the center. On my Tek TDS3032, varying the timebase expands the trace around the trigger point, no matter where it is on the screen. The Rigol behavior seems like more than just a different way of working that I need to get used to, but rather a seriously wrong way of operating. I can't imagine who would want their trigger point to move around when changing us/division? Fortunately I discovered this on someone else's Rigol scope before I bought one. I've never seen this discussed in scope reviews, and never even thought this would be something I had to look out for, but for me it's a show stopper. Does anyone know how Siglent or other low cost brands behave with regard to this? Or maybe there is a Rigol menu setting to fix this?

author: tautech
author_rank: Super Contributor
timestamp: May 07, 2020, 12:47:48 am
content: Yes, X-E Siglents and other late X models allow for a fixed 0s position at all settings.

author: JohnPi
author_rank: Regular Contributor
timestamp: May 07, 2020, 01:47:47 am
content: I don't like that mode either.

author: JDubU
author_rank: Frequent Contributor
timestamp: May 07, 2020, 02:18:49 am
content: Quote from: appsman on May 07, 2020, 12:42:52 amOn my Rigol DS2000 you can change this behavior by going to the "Time" menu (button between the time base knob and the horizontal position knob) and select the "Hor Ref" menu. Here there are three choices for the horizontal reference point. "Center" (default), "Trigger Point", or "User" (move the horizontal reference point anywhere on the x axis of the screen).

author: stafil
author_rank: Regular Contributor
timestamp: May 07, 2020, 02:57:42 am
content: Quote from: appsman on May 07, 2020, 12:42:52 amI tried this on a Tek DPO2000B and see the behaviour you described for Rigol.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 07, 2020, 03:12:40 am
content: that is fixed offset mode, ie you will see signal at the same offset when changing time/div. its usefull when we want to see off the screen signal. i agree with your mode of working, ie when trigger point is at fixed position inside screen area where origin of x-axis will show varying offset, but its maybe asking too much if they have to provide both mode in user selectable setting such as in LeCroy iirc. but your mode will be a PITA when we want long offset trigger far off the screen and analyze event at particular offset. i will say if the dso has dedicated trigger offset reset button like Rigol, i will choose fixed offset mode if only i can choose one. and fixed trigger position if the DSO has clever off the screen trigger scrolling/encoder speed or if it has numeric typed-in offset input box. i wish Rigol has this numeric input box like how we set holdoff or "pulse width" in pulse triggering mode. scrolling off the screen trigger in Rigol to get a precise and quick offset is a PITA, luckily it has a dedicated reset button, unlike LeCroy scope on my bench here (only resetable in SW menu) but has fixed trigger position mode iirc.

author: H.O
author_rank: Frequent Contributor
timestamp: May 07, 2020, 05:00:48 am
content: It would help if you specified which Rigol scope you're talking about but my DS4000 is the same as what JDubU describes - you can set it up the way you want.

author: Fungus
author_rank: Super Contributor
timestamp: May 07, 2020, 06:03:27 am
content: Quote from: appsman on May 07, 2020, 12:42:52 amThe trigger offset is set by time, not by screen pixels Zooming in/outshouldpreserve that.

author: bob91343
author_rank: Super Contributor
timestamp: May 07, 2020, 06:42:09 am
content: My HP digital 'scope does that. It shows the wave starting at the center, and adds pretrigger signals to the left. It can be useful, as sometimes it's hard to trigger exactly where you want.

author: 2N3055
author_rank: Super Contributor
timestamp: May 07, 2020, 06:55:00 am
content: There is one magical trick I will reveal to you.. It's called downloading User Manuals from Internet...(sorry, I kinda had to..)Seriously, it takes two minutes, you search for user manual for a scope in question with your favorite search engine and then using Find function, you find information in another half minute..Doing it for few random scopes takes less time than creating a bad topic on EEVBLOG, that doesn't show you in the best light...People here expect you do little bit of homework before asking it out loud...Just a friendly reminder, not trying to start a fight..And most of thechinesescopes from better brands are more sophisticated and have more features that western scopes in the same price bracket..All the best,

author: Fungus
author_rank: Super Contributor
timestamp: May 07, 2020, 07:14:00 am
content: Quote from: stafil on May 07, 2020, 02:57:42 amQuote from: bob91343 on May 07, 2020, 06:42:09 amnb. Neither of those is "Chinese".

author: BravoV
author_rank: Super Contributor
timestamp: May 07, 2020, 07:28:07 am
content: A xenophobic discussion that is wrapped with scope topic.

author: nctnico
author_rank: Super Contributor
timestamp: May 07, 2020, 11:09:23 am
content: Quote from: appsman on May 07, 2020, 12:42:52 amProbably there is a menu setting. These kind of details are only mentioned in the manual (likely in a chapter with the word 'horizontal' in the name). Having written/done several oscilloscope reviews myself I never felt the need to touch this topic.

author: eutectique
author_rank: Frequent Contributor
timestamp: May 07, 2020, 11:46:40 am
content: Quote from: appsman on May 07, 2020, 12:42:52 amYou did not tell which scope you are massaging, but on MSO5000 this can be done. User's Guide page 4-10, "Horizontal Expansion".Acquire->More->ExpandHope this helps.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: May 07, 2020, 01:10:37 pm
content: Quote from: appsman on May 07, 2020, 12:42:52 amThis is quite common with modern DSOs, although the better ones allow the user to configure if the trace shall expand from the trigger point or the screen center.The reason is that, quite oftn, your point of interest is actually not close to the trigger but somewhere else, and if you then reduce the timebase as a means to get more detail it's more useful if what has been in the middle of the screen actually stays there than shifting outside (which is what happens when the trigger point is the reference point). So there is some use to this.But on most better scopes this should be configurable.

author: tautech
author_rank: Super Contributor
timestamp: May 07, 2020, 02:26:07 pm
content: Those with a touch display make this dead simple.

author: nfmax
author_rank: Super Contributor
timestamp: May 08, 2020, 08:27:38 am
content: Quote from: Wuerstchenhund on May 07, 2020, 01:10:37 pmIsn't it interesting to find old analogue habits persisting in the language we use? On a DSO, there is no such thing as a 'timebase'. The corresponding controls are the horizontal (or time) scale and position, and are generally labelled as such. When used 'live', in 'run' mode they may operate similarly, but after a single shot acquition they become pan and zoom controls (possibly in addition to the dual-scale display that is usually called zoom). There is similar confusion over the vertical scale and position controls. Do they change the actual voltage applied to the ADC input or just change how the results are plotted on screen? Really, two different functions!

author: 2N3055
author_rank: Super Contributor
timestamp: May 08, 2020, 09:03:21 am
content: Quote from: nfmax on May 08, 2020, 08:27:38 amWell, same like with horizontal, in RUN mode it will control attenuators/amplifiers and fine screen scaling, and in stop mode only screen scaling, obviously..There is much confusion, I agree. I think there are 3 roles that users expect from digital scope: to act as analog ones did (together with all connected idiosyncrasies), to be digital interactive scope ( an interactive display device but with added functions of digital scope), and a digital sampling unit data acquisition device (capture single shot and analyse).Naturally no concept will be very good for all three roles..For instance Keysight Infiniivision series is excellent at first two, Lecroy is excellent for 3rd and very good for 2nd.Picoscope is excellent for 3rd, and usable for 2nd role .. etc ....To have device excellent in every role, you will need more than one device...

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: May 08, 2020, 09:37:55 am
content: Quote from: nfmax on May 08, 2020, 08:27:38 amYes, but it's not surprising when analog scopes had more than half a century to burn their terminology into our brains'Timebase' is still correct, just that it's now the timebase of the (dynamically updated) display only (it doesn't just control time per division but also to some extend the update speed).Also, the vertical controls do actually affect change in the front end (i.e. RF switches, attenuators) and the vertical position is often affecing a bias voltage for the ADC.One of my pet peeves is horizontal scale ('timebase') knob used for zoom. It just doesn't make logical sense to me and I much prefer separate zoom controls as found on LeCroy scopes. It's one of the many things which LeCroy does different which shows it originated from the science corner and not EE, and which fit better to my way of thinking.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: May 08, 2020, 09:56:25 am
content: Quote from: 2N3055 on May 08, 2020, 09:03:21 amThere are essentially two categories of scopes:- Entry-level scopes, usually all low BW, with limited functionality and which are designed to replicate the behavior of analog scopes so they can be used by people who were trained on analog scopes; in this class, trigger rate is very important- More advanced scopes (analysis scopes) where analysis and measurement capabilities are the main focus and the trigger rate is not very relevant unless it's excessively low.However, thanks to technology becoming better and ever cheaper, we have seen some of the functionality of the second group to become available in the first group.QuoteIt's not really a question of which is better in which situation.Don't forget that, back in the analog days, people mostly had to work around the many limitations of an analog scope, which is reflected in the methodology. But digitization then enabled a new world of ways to analyze signals, and the methodology from back then is simply inadequate for digital scopes.However, because a large number of people were trained on analog scopes, and many tasks could still be achieved with analog scopes, it made sense to replicate analog methodology on entry-level scopes so obsolete analog scopes could be replaced with a DSO without requiring the user to re-learn methodology.However, we are now at a point where new engineers have been trained on DSOs exclusively, so there is no "analog memory" worth preserving. But we still drag on analog methodology for the simple reason of "it's always been done this way".Eventually, however, it will die out.

author: David Hess
author_rank: Super Contributor
timestamp: May 09, 2020, 03:54:42 am
content: All of the DSOs I have used behave the same way. When using a dual delayed timebase, expansion occurs centered on the trigger point. But the same DSO using magnification expands around the center of the display. Incidently, analog oscilloscopes work this way as well because magnification is done late in the horizontal signal path.Modern DSOs which rely on magnification to replace a dual delayed timebase could of course have an option to magnify around the trigger position to simulate the behavior of a dual delayed timebase.