Out of curiosity, are there DSOs with alternate trigger? - Page 1
Forum section: electronics / testgear

author: JPortici
author_rank: Super Contributor
timestamp: December 23, 2016, 10:20:45 am
content: From time to time i have *unusual* tasks, at least unsual for a dso.i have a device which has a square wave as an input and it produces a square wave of a different frequency, depending on a parameter... for example 1 KHz in, param=100 -> 900 Hz outI'd like to see them both clearly, this would be an easy task for almost any CRO: alternate trigger. but none of the DSO i have at work or at home seem to be able to do it.. and none that i can think of, so the question: which DSO have alternate trigger? I remember an old topic that mentioned some but i can't find it

author: EEVblog
author_rank: Unknown
timestamp: December 23, 2016, 10:36:43 am
content: I think the original Rigol DS1054 had it, as does one of the Hamegs or something?

author: Daruosha
author_rank: Regular Contributor
timestamp: December 23, 2016, 10:44:45 am
content: Dave ment DS1052E,Crappy owon SDS series have alternate trigger as well.

author: rf-loop
author_rank: Super Contributor
timestamp: December 23, 2016, 10:45:31 am
content: Siglent SDS1000CMLIt have rareDual TimebaseAlternate trigger mode with full independent trigger system for both channels.Rigol DS1000E do NOT have. It have only Single timebase ALT.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: December 23, 2016, 01:49:04 pm
content: I've checked two scopes here in the lab - both Agilent DCO1014A and Tektronix MDO3104 have it.CheersAlex

author: nctnico
author_rank: Super Contributor
timestamp: December 23, 2016, 02:13:54 pm
content: GW Instek 2000E series for sure (I've used it) and probably others models as well. But you have to realize that with alternate triggering you are looking at traces without any relation because they are not sampled at the same time. If a rare anomaly causes a problem you will see it in only one trace.

author: TheoB
author_rank: Regular Contributor
timestamp: December 23, 2016, 02:34:30 pm
content: Ah, I didn't miss it yet but this is the second thing I 'assumed' would be present on the DS1054Z. The first one being variable time base.I guess the workaround is to trigger on one signal, save it to a reference and then trigger to the other signal. That's what my old CRT scope could not do. Of course not exactly the same, but for a one time view of two asynchronous signals, this might work.

author: JPortici
author_rank: Super Contributor
timestamp: December 23, 2016, 05:44:44 pm
content: Quote from: nctnico on December 23, 2016, 02:13:54 pmof course! it's alternate trigger. I remember you already mentioned the 2000E would be able to but when i checked the manual i couldn't find anything in the trigger section@TheoB yours was the topic i referred to before

author: MrWolf
author_rank: Regular Contributor
timestamp: December 24, 2016, 01:16:47 pm
content: Hm, did you not have something to do with Picos? No problem there...Alternate trigger from PWM and resulting sine to keep it nice and aligned.Of course it could be done with just PWM window triggering in this specific case, but will do as quick example.

author: nctnico
author_rank: Super Contributor
timestamp: December 24, 2016, 01:29:23 pm
content: The PWM and sine are related. Alternate triggering is used to show two unrelated signals.

author: MrWolf
author_rank: Regular Contributor
timestamp: December 24, 2016, 01:53:33 pm
content: Quote from: nctnico on December 24, 2016, 01:29:23 pmHere 2 triggers are used:1)rising levelfor PWM to keep edge atexactly0s2)max levelfor sine to keep sine "hump" atapprox0s, sine is too unstable to do precise triggering, especially at zero crossing.So signals ale related, but pretty vaguely.Stable triggering cannot be done using either one of the specific triggers individually.But yolo, if you still do not understand point of example its just fine by me

author: JPortici
author_rank: Super Contributor
timestamp: December 24, 2016, 03:28:38 pm
content: as i'm using a pico2000 on the workbench i have to ask: how did you set up the trigger, exactly?i want to see two stable square waves, each at an arbitrary frequency.

author: MrWolf
author_rank: Regular Contributor
timestamp: December 24, 2016, 03:52:51 pm
content: Well nobody said you cant use digital logic triggers on analog signals

author: MrWolf
author_rank: Regular Contributor
timestamp: December 24, 2016, 11:56:28 pm
content: Since it interesting to max out hardware at hand did additional test:f1 = 3.3VDC 48kHz square CH1f2 = 2Vpp 51Hz sine CH2f1 mod f2 <> 03 orders different frequency triggering no prob withCH1.Rising(1.65V) AND CH2.Rising(0V).2% hystersis did give most stable result.

author: Howardlong
author_rank: Super Contributor
timestamp: December 25, 2016, 01:13:51 am
content: The Owon HDS3102m-n does alternate trigger mode.I am not convinced that there is some confusion in some of the above posts between alternate triggering, where the traces operate in Alt mode, with a different trigger on each trace (so you can see two uncorrelated signals), and a logic or delayed trigger.For example, I don't know how you'd set up an MDO3000 to do Alt triggering, and the Pico examples look like logic triggers, which aren't the same as alt triggering.

author: MrWolf
author_rank: Regular Contributor
timestamp: December 25, 2016, 10:06:06 am
content: Hm, if there is some feature on some scope where you can have twonot-time correlated traces (dual trace on CRO?) with full reso each and full hardware triggering on each then Pico does not do that. However this sort of loses point of showing the traces on same scope, no? I have just hooked two Picos to same PC for that and opened 2 instances of software on same screen.But where there is some correlation point in time* it just comes down to scope memory amount (in Pico case). My old box has only 48kS so this sets maximum diff of frequencies to about 3 orders of magnitude. 2408B has 128MB would be interesting what that could do...Anyway I did provide examples becasue OPs case seems trivial to solve with alternate logic triggers which work just as well on any analog signal.Edit: *actually if you do logic OR or whatever they do not have to be correlated at all.

author: Howardlong
author_rank: Super Contributor
timestamp: December 25, 2016, 10:20:09 am
content: It is a rare scenario. But it's also the reason why we all need 20 oscilloscopes.

author: MrWolf
author_rank: Regular Contributor
timestamp: December 25, 2016, 10:27:01 am
content: Quote from: Howardlong on December 25, 2016, 10:20:09 amThink having ridiculous amount of mem on DSO would work around that in most cases. Gotta try it sometime. Torture testing is fun.Anyway, specifically for OP who has Pico on desk logic indeed seems to solve it. With triggering on each channel with normal triggers other channel is "running around". Looking for some correlation freezes them real well, 48kHz + 52kHz:

author: rf-loop
author_rank: Super Contributor
timestamp: December 25, 2016, 10:48:36 am
content: Quote from: MrWolf on December 25, 2016, 10:06:06 amAs told previously.Old Siglent SDS1000CML have.It have ALT mode where both traces have fully separate independent triggers. And even more. Both traces have independent time base. It is Dual Timebase ALT mode. Many scopes have ALT mode with separate trigger but not with independent time base.Pity they have not implemented this for full digital triggering system models.Most analog scopes have ALT mode but still only one beam. One beam is altered between channels and triggered separaately. Disadvantage is that other trace need wait other trace trigged and sweeped.And same in most digital scopes what have ALT. One trace trigged and acquire and one trace wait. They can not simultaneously but independently capture with independent time bases and independent triggering. For this we need two scopes and watch two separate displays what is not always fun.There is also true dual beam analog scopes. These have one crt but fully two separate electron gun (two independent beam inside one tube with also separate independent deflection. (One example is Tektronix 7844 - I have one this beauty)Where is this kind of DSO? Who knows if there is.

author: nctnico
author_rank: Super Contributor
timestamp: December 25, 2016, 11:46:18 am
content: Quote from: rf-loop on December 25, 2016, 10:48:36 amNot entirely true. Zoom mode allows to see signals at different time bases.

author: MrWolf
author_rank: Regular Contributor
timestamp: December 25, 2016, 01:00:11 pm
content: Quote from: Howardlong on December 25, 2016, 10:20:09 amThink I f****d it all up, again!OP probably just wanted excuse for a new toy from a bossJust like Church of Z sectants want to hear "Z is dope" couple times per day instead of performance tests

author: David Hess
author_rank: Super Contributor
timestamp: December 25, 2016, 01:19:45 pm
content: Quote from: Howardlong on December 25, 2016, 01:13:51 amWhen I was evaluating the Tektronix MSO5000 series, the sale engineer and I could not figure out how to do alternate triggering or timebases. All of my analog oscilloscopes and most of my DSOs support alternate triggering and of course my 4-bay 7000 mainframes can operate as two independent oscilloscopes with the same display.Quote from: Howardlong on December 25, 2016, 10:20:09 amThat was basically my solution. If I need alternate triggering and digital storage, then I use two of the same or different DSOs.

author: StillTrying
author_rank: Super Contributor
timestamp: December 25, 2016, 10:08:15 pm
content: "Old Siglent SDS1000CML have."Alternate triggering/dual timebase is still there in the CML+.It only works on RT sampling and only on the short 40k memory, but as it can use a different sampling rate for each traces' timebase I don't think there's any limit to the difference between the two timebase speeds.

author: mk_
author_rank: Regular Contributor
timestamp: December 25, 2016, 10:34:15 pm
content: Quote from: Alex Nikitin on December 23, 2016, 01:49:04 pmcan you show or explain how you did it on the MDO3104? I needed it some weeks ago and didn`t find a way to trigger on signal at Ch1 and an more or less independent signal on Ch3 (which is no problem on my analog Iwatsu)Michael

author: JPortici
author_rank: Super Contributor
timestamp: December 26, 2016, 08:05:43 am
content: Quote from: MrWolf on December 25, 2016, 01:00:11 pmahaha no, i already have the amount of scopes i need, if anything i'm looking for excuses for other kind of equipment but not scopes.i admit i never even bothered to check out the logic trigger on the pico, after i found out it wasn't referring to serial triggering (which i was hoping to)but yours looks like a good trick. will try wednesday at the workbench

author: Howardlong
author_rank: Super Contributor
timestamp: December 26, 2016, 10:29:04 am
content: Quote from: mk_ on December 25, 2016, 10:34:15 pmI agree, ISTBC, but I don't think it's possible. I suspect it's the confusion of that scope's dual A/B trigger functionality with what an alt trigger is.

author: David Hess
author_rank: Super Contributor
timestamp: December 26, 2016, 03:59:30 pm
content: Quote from: Howardlong on December 26, 2016, 10:29:04 amThe confusion might be well deserved. On some oscilloscopes with A and B sweeps and triggers, it is possible to use alternating A and B sweep with separate A and B sweep triggers to do alternate triggering.

author: guenthert
author_rank: Frequent Contributor
timestamp: December 26, 2016, 07:10:46 pm
content: I must admit, I don't quite understand the use case. Isn't this solved with any storage oscilloscope (or sufficiently fast data acquisition system) using single shot, triggered on either signal? Isn't this (one of) the reasons why a great number of stored samples is desirable?

author: JPortici
author_rank: Super Contributor
timestamp: December 26, 2016, 11:27:13 pm
content: Quote from: David Hess on December 26, 2016, 03:59:30 pmwell, alternate is pretty straightforward:alternatesbetween two [...]betweens two what? there lais the confusion. in my case i think at alt trigger as it's implemented in my tek 7000 mainframe, which is one of the following:- Trigger from and show only channel a or b, alternatively. trigger is the same, source is different- Trigger from and show only channel a or b, alternatively. different trigger settings.- Trigger from the same channel, different trigger settings.Option 1 is what i'd need.. and i think it's perfectly doable with a DSO but i didn't know many that implemented this function

author: David Hess
author_rank: Super Contributor
timestamp: December 27, 2016, 06:45:45 am
content: Quote from: guenthert on December 26, 2016, 07:10:46 pmA digital storage oscilloscope can do that but alternate triggering allows both waveforms to be stably displayed in real time with the trigger in phase with each waveform separately even if the waveforms are asynchronous with each other.Examples include viewing the switching or ripple of two separate unsynchronized switching regulators at the same time. Or viewing a switching regulator waveform and a separately clocked logic signal.Quote from: guenthert on December 26, 2016, 07:10:46 pmAlternate trigger means that when alternate instead of chop is used in dual trace mode and the trigger source is set to vertical, the trigger source follows which trace is currently being displayed. This was an possibly unintended but useful consequence of early oscilloscope designs where the vertical trigger source selection meant literally that; the trigger source was taken from the vertical signal *after* the vertical channel switch. Even earlier designs may have *only* had vertical triggering so always operated in alternate trigger mode. Later designs like the 7000 series emulated this behavior because it was a useful feature.Alternate sweep means that in dual trace mode, the A sweep and A trigger display one trace and the B sweep and B trigger display the second trace. The oldest oscilloscope that I know of which can do this is the Tektronix 547. This mode emulates a true dual beam oscilloscope with separate sweeps and triggers but requires only one beam.Alternate delayed sweep is something else which displays the same set of signals with two different sweeps. This is the famous mode where one sweep shows an intensified zone while the second sweep shows the contents of the intensified zone effectively magnifying that part of the slower sweep. Early delayed sweep oscilloscopes could display one sweep or the other but not both alternately. Sometimes alternate delayed sweep can be used to emulate alternate sweep.QuoteThe Tektronix 7000 series has unusually flexible triggering and alternate triggering in the traditional sense was deliberately included on multiple levels. The mainframe can alternately trigger between vertical plug-ins and dual input vertical plug-ins can also alternately trigger between inputs.The 7000 series also support alternate sweep with the same signals displayed with different sweeps and triggers and alternate pairs with different signals displayed with different sweeps and triggers. The dual beam 7844 (and the older dual beam 555 and dual beam 556?) took these capabilities to an extreme.As pointed out by other posters, some modern DSOs support alternate triggering. My old 22xx series DSOs which use analog triggering support alternate triggering simply because the original analog trigger design did also.

author: JPortici
author_rank: Super Contributor
timestamp: December 27, 2016, 06:22:35 pm
content: Quote from: David Hess on December 27, 2016, 06:45:45 amand i LOVE my 7k.Quoteand i wanted to know which one, or what fancy name they used for it... and i may also found out an interesting alternative way to do it with a picoscope, which i have, that i'll check tomorrow

author: guenthert
author_rank: Frequent Contributor
timestamp: December 27, 2016, 06:30:04 pm
content: Quote from: David Hess on December 27, 2016, 06:45:45 amAnd you can't do that when you have acquired the data in a single shot? You can take than all the time you like to see those waveforms 'stable'. I don't quite see the value of seeing two asynchronous waveforms 'in real time' (and typically much, much faster than the eye could follow).I get the impression that you (and op) try to apply procedures used to get around limitations of analog oscilloscopes to storage 'scopes. For the former single shot is only marginally useful (w/o camera virtually pointless), for the latter it is very useful. New possibilities, new procedures.I do see the value of triggering on a combination of both signals, as demonstrated earlier in this thread using the picoscope. That's a feature, I'd like to see in my 'scope.Quote from: David Hess on December 27, 2016, 06:45:45 amThat wasn't me, your post mixed up the quotes (sadly easy enough to do using this forum's software).

author: MrWolf
author_rank: Regular Contributor
timestamp: December 27, 2016, 06:59:58 pm
content: Quote from: guenthert on December 27, 2016, 06:30:04 pmPerhaps when doing digital data signal analysis single shot is ok, because carrier stays at same freq... but when looking at PWM, motor drivers etc it is all varying and sometimes pretty fast. I have done a lot of fiddling with custom made motors and pretty typical case is messing with Hall sensor position (outputs square of independently varyingperiod+Duty and frequency), while keeping an eye on coil voltages/currents.

author: guenthert
author_rank: Frequent Contributor
timestamp: December 28, 2016, 12:33:56 am
content: Quote from: MrWolf on December 27, 2016, 06:59:58 pmBut aren't fast changing signals more a reason to evaluate them off-line? Hmmh, sorry, I don't have done enough of any of this to fully grasp the problems occurring in application.

author: JPortici
author_rank: Super Contributor
timestamp: December 28, 2016, 01:11:37 am
content: this case is square wave at arbitrary frequency in -> square wave at frequency + delta out. both frequency and delta may vary dinamically.to be honest, i don't actually need alt trigger for this, infact the job was done.but if i had my tek mainframe at work i would have used alt trigger, stable display of in and stable display of out

author: David Hess
author_rank: Super Contributor
timestamp: December 28, 2016, 04:14:54 am
content: Quote from: guenthert on December 27, 2016, 06:30:04 pmReal time does not have to mean fast. Alternate triggering allows stable continuous observation of two or more separate and unrelated signals. This is especially convenient when adjustments or changes in conditions affect both signals. It would be tiring to have to hit run/stop or single sequence all the time and even then, the untriggered waveform is going to jump around.QuoteThis is a limitation of mostdigitalstorage oscilloscopes and fewanalogstorage oscilloscopes. Think of it as an alternative to requiring two separate oscilloscopes, even digital storage oscilloscopes, in certain applications. It is a more difficult feature to include in a modern digital storage oscilloscope than an oscilloscope which uses analog triggering where it is practically free and this may explain its rarity in modern instruments.The onlyprocedurewhich replaces alternate triggering is thepossibilityof using a second oscilloscope which while satisfying, may be difficult to justify economically. Sometimes that is the only way however. When I decided that I needed a 4 channel DSO, the cheapest good option was to buy two separate 2 channel DSOs.

author: JPortici
author_rank: Super Contributor
timestamp: December 28, 2016, 09:23:17 am
content: tried the logic trigger thingy on the picoscope, it's no substitute for alternate trigger (no stable display of the two waveforms, it's a bit jittery) but the situation has really improvedmy setting wasA rising OR B rising

author: MrWolf
author_rank: Regular Contributor
timestamp: December 28, 2016, 10:13:05 am
content: Quote from: JPortici on December 28, 2016, 09:23:17 amHm, I did try only AND, with two different frequs there will be correlation point always, only question is how oftenQuote from: JPortici on December 28, 2016, 09:23:17 amSometimes tweaking the trigger levels and especially hysteresis helps. With PWM sine applying 12bit smoothing really helped. So indeed its not a Tek mainframe but tasks can be still accomplished.Currently Im playing with derivatives on math channels which greatly amplifies any jitter/noise present. There seems to be small noise related to sampling rate. Probably this is one culprit with logic triggers. On math channel 25MHz low pass gets rid of it.

author: KlausF
author_rank: Contributor
timestamp: November 26, 2018, 10:01:38 pm
content: Strange. Can anyone figure out a reason why there is no alternate trigger any longer? For me, that´s crazy.All the crappy cheap scopes have it.MrWolf wrote, picoscope has it, but that is actually not true. Picoscopes do NOT have alternate trigger.

author: David Hess
author_rank: Super Contributor
timestamp: November 28, 2018, 01:00:33 am
content: There is less need for it if you can simultaneously sample and a single sweep is acceptable which all DSOs have been able to do for a long time.A real time alternate display requires more hardware like dual triggers and timebases adding to the expense although these already exist if the DSO supports a delayed timebase with trigger after delay.