Why so many 4 Channel scopes dont have an Ext. Trigger? - Page 1
Forum section: electronics / testgear

author: Trax
author_rank: Regular Contributor
timestamp: July 25, 2015, 05:44:19 pm
content: I'm wondering why so many (not only cheep) 4 Channel scopes dont have an Extern Trigger input?A plausible explanation might be really enlightening

author: electr_peter
author_rank: Unknown
timestamp: July 25, 2015, 06:10:45 pm
content: Reason are pretty obvious - space and price constraints. 4 ch scopes are typically very cramped with LCD, BNCs and buttons. Also, manufacturer have to dedicate "fifth" dummy channel for triggering which adds to the complexity of the scope significantly.Lack of external trigger means you can either use 4 ch without external trigger or 3 ch with external trigger. Cases when you need 4 ch + ext trigger are rare. If you are desperate to have 4 ch + ext, either buy scope that allows that or rig up two scopes to have >=4 ch.

author: tautech
author_rank: Super Contributor
timestamp: July 25, 2015, 07:54:50 pm
content: Quote from: electr_peter on July 25, 2015, 06:10:45 pmThis is an unusual POV.These days the EXT BNC is usually on the rear and therefore has no effect on the valuable front panel real estate.Unless a 4 ch scope has external trigger, it can't be called well featured.The only reason to omit it iscost.Nearly all scopes have a line trigger, how hard is it to add an external trigger , additional signal path, BNC connector and/or someto FW and the UI.These things are easy when compared to the overall complexity of scope design.All scopes should have it IMO, even entry level models.

author: Trax
author_rank: Regular Contributor
timestamp: July 25, 2015, 08:14:37 pm
content: How realistic do you think would it be to tap into the line trigger circuit and re-purpose it as external trigger.Would it be as accurate as a real one?

author: tautech
author_rank: Super Contributor
timestamp: July 25, 2015, 08:19:11 pm
content: Quote from: Trax on July 25, 2015, 08:14:37 pmFoolish.Line trigger is an important feature, don't muck with it.Share with us your external trigger needs and there may be another method to achieve the result you need.

author: SeanB
author_rank: Super Contributor
timestamp: July 25, 2015, 08:20:51 pm
content: To be a decent trigger it would have to have the analogue front end of the other channels, so using a channel as a trigger is going to work in the majority of cases, and as a bonus it also will have a useful function when not being used as a trigger input. Line trigger in most cases has only limited bandwidth, and will have a fixed trigger level in most cases as it will, in most modern scopes, be a digital signal out of the power supply.

author: rollatorwieltje
author_rank: Unknown
timestamp: July 25, 2015, 08:52:58 pm
content: Isn't it a bit of a relic of the analog age? I mean, I only really found myself using the trigger channel on analog scopes as a crude "pre-trigger", to see what happens just before the interesting part. Digital scopes store stuff before the trigger point as well, so it's good enough to trigger on the actual data.On my DS1052E I do use it, but that's just a 2 channel scope.

author: electr_peter
author_rank: Unknown
timestamp: July 25, 2015, 09:00:14 pm
content: Quote from: tautech on July 25, 2015, 07:54:50 pmWell, modern scope typically has all the inputs in a neat single row on the front panel. Rear panel may have some BNCs and auxiliary connections, but it is considered not as accessible as the front panel. Such design limits designer options to include additional inputs/outputs.Contrast this with older CROs where front panel BNCs are almost in random places and there may be myriad of connections on the back. My current 2 ch CRO has 2 external trigger inputs on the front and 4 additional BNCs on the back - and I still consider it to lack some connectivityAs noted in my previous post, I agree that main driving force behind missing ext trigger on 4 ch scopes is cost/complexity. Manufacturers are gambling a bit - they know that most users in most cases won't require 4 ch + ext trigger setup, so they offer "more affordable" compromise.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: July 25, 2015, 10:32:49 pm
content: Quote from: Trax on July 25, 2015, 05:44:19 pmI'm not sure what you're talking about, because aside from maybe some cheap bottom-of-the-barrel and some entry-level scopes an external trigger input is still pretty much standard on most modern scopes.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: July 26, 2015, 01:17:44 am
content: How often does someone actually need 4 channels + an external trigger off of a fifth signal?My Rigol DS1054Z is a three-channel scope with external trigger, or a 4 channel scope without it. That is plenty for me.I do find the external trigger on my 2 channel analog scopes to be useful from time to time, and the delayed external trigger on the old HP180a with 1821a timebase has been useful at times as well.I agree, though about the "Line" trigger (or Source AC on the Rigol). This is an extremely useful and necessary function, more so than a 5th trigger channel on a 4 ch scope would be.

author: Trax
author_rank: Regular Contributor
timestamp: July 26, 2015, 07:26:47 am
content: Quote from: tautech on July 25, 2015, 08:19:11 pmWhy? Who needs Line trigger nowadays?I don't have any particular needs at the moment, that would require 4 CH + Ext, I'm just course.Quote from: SeanB on July 25, 2015, 08:20:51 pmYes i know thats just a wire from the scopes PSU, but the question is can you attach the wire to some self made front end and use it. You could even add some Schmitt trigger circuit to be able even to set the level.Quote from: Wuerstchenhund on July 25, 2015, 10:32:49 pmHameg HMO2024 -> 2k$Keysight DSOX3000 -> 4k$thay are not so cheep or so entry and thay dont have a ext trigger

author: rs20
author_rank: Super Contributor
timestamp: July 26, 2015, 07:41:13 am
content: Quote from: tautech on July 25, 2015, 07:54:50 pmThis is a bit of a tautology, the reason for omittinganyfeature is cost. I think the more complete answer to the OP's question is "diminishing returns": the value to the end user of that extra trigger channel is lower on a 4ch scope than a 2ch scope, because circumstances where you need to view/trigger a total of 3 channels are much more common than the circumstances when you need to view/trigger a total of 5. So it's that thecost/benefit tradeoffdoesn't make the cut, not because the manufacturers are just completely arbitrarily cutting costs.Put another way, if you have 4 channels to begin with, you can just dedicate one of those channels to triggering and have a 3 channel scope; saying the same for a 2ch scope (dedicate one for triggering and you're left with 1 ch) is obviously far more damaging to the usability of the instrument.Put yet another way, think of a 2ch scope with ext trigger as a "3 channel scope with a crippled, trigger-only third channel". Now a non-crippled, 4 channel scope doesn't sound so unpalatable.Ithinkmy TDS 754C has an external trigger on the back, but I don't really know because I've never used it

author: EEVblog
author_rank: Unknown
timestamp: July 26, 2015, 07:53:23 am
content: An external trigger is actually a compromise, always has been and still is.Full channels are better, as you have a full attenuator and you can view the signal.It's pretty much essential on a 2CH scope, but when you go to the expense of a 4CH, that need diminishes greatly, so not much need to spend any extra on the ext trigger. Been that way since the days of analog scopes.Take the Tek 2465, best analog scope ever made, spared no expense, no external trigger.

author: mikron
author_rank: Contributor
timestamp: July 26, 2015, 07:57:48 am
content: Quote from: Trax on July 26, 2015, 07:26:47 amBoth have EXT TRIG IN and TRIG OUT on the back.

author: tautech
author_rank: Super Contributor
timestamp: July 26, 2015, 08:01:02 am
content: Quote from: Trax on July 26, 2015, 07:26:47 amAnybody working with mains frequency referenced equipment.Anybody examining ripple in a linear PSU.Line Trigger FORCES triggering at line frequency, very useful on occasions.You may or may not be aware many scopes these days can operate from supplies ranging from ~45 to 400 Hz, wouldn't Line triggering be useful over that range.Fact is it's all internal, cost little to implement and arguably more useful than Ext trigger, however IMHO both are a necessity in a decent scope.You might ask the same question as why various video trigger modes are included in scopes these days with the prevalence of new formats like HDMI.Quote from: rs20 on July 26, 2015, 07:41:13 amQuoteIsn't all this JUST another selection criteria one must apply to a prospective new scope.Years ago before LA's a 4ch scope with Ext triggering WAS your LA and for those that can't justify a separate LA unit these days, a scope with Ext trigger is an attactive option.Used that senario several times myself.

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2015, 08:23:35 am
content: Quote from: tautech on July 26, 2015, 08:01:02 amMost Tek scopes came with the option of a wide input frequency range, which in most cases was very easy to implement, they changed the input mains filter to one with a lower value X capacitor so it would not overheat at 400Hz. The mains transformers were good enough in most cases to not saturate at 45Hz, and still not have excessive core loss at 440Hz. You design it for low copper loss and are very conservative in the power rating for the core.When they started to use SMPS designs you also got some with a very wide input range, 65VAC to 260VAC, 40 to 480Hz and also capable of operation from 28VDC to 300VDC. No configuration required.

author: dom0
author_rank: Super Contributor
timestamp: July 26, 2015, 08:27:27 am
content: Quote from: rollatorwieltje on July 25, 2015, 08:52:58 pmNo, external trigger is /extremely/ handy when tracing signals through complex circuits, because you only need to adjust V/div and maybe offset, while the trigger just runs off the SYNC output of the generator and doesn't need any adjustment. Without external trigger you'd need to adjust the trigger as well.One can also use another input channel for this, but whether you can hide it on screen and still trigger on it depends on the scope. And it obviously costs you a trace.

author: Howardlong
author_rank: Super Contributor
timestamp: July 26, 2015, 09:15:59 am
content: Why only one external trigger when you can have two?

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: July 26, 2015, 10:16:23 am
content: Quote from: Trax on July 26, 2015, 07:26:47 amAre you kidding? Both have external Trigger inputs (see HMO202x manual p.13 and p42 of the DSOX3k manual).And frankly, if you think $4k is expensive for a scope then you haven't seen much.

author: Zero999
author_rank: Super Contributor
timestamp: July 26, 2015, 10:43:22 am
content: Quote from: SeanB on July 26, 2015, 08:23:35 amHmm, I wonder what the minimum operating voltage of the Rigol DS1054Z is. It's probably lower than what it says on the datasheet. It would be good if it would work from 48VDC so could be powered from some lead acid batteries.

author: dom0
author_rank: Super Contributor
timestamp: July 26, 2015, 10:55:37 am
content: Most world-wide SMPS can't sustain output regulation or shut down below 80-90 Vdc.

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2015, 11:15:51 am
content: I was surprised as well when I got a Tektronix at work. Just had to power it on the 28VDC supply bus, and it worked perfectly, as well as working on the 115VAC 400HZ supply from the wall. Either they ordered it with all the options or it was standard for the range delivered to my employer at the time.I had a call from the original group that had placed the order and then neglected to collect it for 2 years in the stores group. I referred them to my boss, and his reply was to go sit on something sharp. They had to order the 2 scopes again on the budget...........

author: tautech
author_rank: Super Contributor
timestamp: July 26, 2015, 11:27:25 am
content: Had a BWD CRO that could be powered by 30V DC as part of diagnosing the pre_regulator, it even derived the CRT HV from it.

author: Zero999
author_rank: Super Contributor
timestamp: July 26, 2015, 06:46:06 pm
content: I've just tested my Rigol DS1054Z on DC. It works from 4 lead acid batteries to give 47VDC (one was a bit flat). I tried with three batteries but it didn't work.I might build myself a battery pack for it.

author: dom0
author_rank: Super Contributor
timestamp: July 26, 2015, 06:54:03 pm
content: Tried it on my Hantek DSO5102B:Doesn't do anything until 100 Vdc.But if it's running, it only turns off after going below ~45 Vdc.Crashes if continually kept around 46-48 Vdc.Advertised as 100-240 Vrms, 45 - 440 Hz. So that's totally fine.

author: Zero999
author_rank: Super Contributor
timestamp: July 26, 2015, 07:02:00 pm
content: Quote from: dom0 on July 26, 2015, 06:54:03 pmIt's odd isn't it? The Rigol isn't specified below 100VAC.I just tested it with a bench supply, plus a couple of SLAs (32V is the maximum I can get from my homebrew LM317 supply) and it starts rebooting below 36V. It's perfectly suited to 48VDC operation though.I haven't measured the current though, as my decent multimeter is at work at the moment.

author: dom0
author_rank: Super Contributor
timestamp: July 26, 2015, 07:07:03 pm
content: Not much. Didn't watch the meter, the 5102 pulled 270 mA or so at 70 V or so. That's maybe 15... 20 Watts.Luckily these Chinese DSOs aren't old LeCroys or Tektronices(?).So with a little "starter" circuit one might even use the Hanteks off 48 V. Or the low-voltage turn-on inhibitor might be removed from it's PSU. Or one could replace it entirely...

author: Howardlong
author_rank: Super Contributor
timestamp: July 26, 2015, 09:33:25 pm
content: I can't say I can ever remember missing it particularly despite using these scopes for many years, but the Tek 2465 series has no external trigger input.The entry level scope in the range was priced at about $11k in today's money, with the 2467 about $23k.

author: zapta
author_rank: Super Contributor
timestamp: July 26, 2015, 10:17:26 pm
content: Quote from: Trax on July 25, 2015, 05:44:19 pmLook again. Sometimes they are labeled CH4.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 27, 2015, 07:56:22 am
content: Quote from: tautech on July 25, 2015, 08:19:11 pmI've always thought the video trigger modes are bit of a waste of space on most reasonable Oscilloscopes,as they can trigger quite easily on Composite Video using Normal triggering.The 7B53A plugin on my Tek 7613 doesn't have a video trigger option,but my cruddy little Jaycar single channel CRO does.By the way,a sneaky trick to trigger "very close to" synch with field rate is to use "Line Trigger"(that must be confusing to newbies!)Obviously field rate & mains frequency aren't exactly the same,nor in phase,but the drift caused by the difference is very ,very,slow.

author: tautech
author_rank: Super Contributor
timestamp: July 27, 2015, 08:11:08 am
content: Quote from: vk6zgo on July 27, 2015, 07:56:22 amGotcha......very sneaky.

author: coppice
author_rank: Super Contributor
timestamp: July 27, 2015, 08:43:08 am
content: Quote from: tautech on July 26, 2015, 08:01:02 am400Hz operation has always been a key feature of most instruments from big makers. Without that they would be locked out of defence applications, which is where they have traditionally made much of their money.

author: Fungus
author_rank: Super Contributor
timestamp: July 27, 2015, 12:11:21 pm
content: Think a a two-channel-scope-with-external-trigger as a scope with 2.001 channels (ie. two full-feature channels plus a very limited third one)A four channel scope can do all that plus a whole lot more. So long as it has a trigger-out you can still daisy-chain multiple units to make a massive multi-channel scope.

author: tautech
author_rank: Super Contributor
timestamp: July 27, 2015, 01:01:48 pm
content: Quote from: coppice on July 27, 2015, 08:43:08 amOf course, I was just checking members knowledge.I even have a few Siglents in Avionic institutions.

author: Electro Fan
author_rank: Super Contributor
timestamp: July 27, 2015, 02:47:02 pm
content: What are the 3-4 most common uses and cabling configurations of trigger out?

author: dom0
author_rank: Super Contributor
timestamp: July 27, 2015, 03:09:44 pm
content: - Synchronizing multiple scopes to have more channels- Accurately counting trigger frequency- (A bit like 1.) having a main / delayed setup with separate single TB scopes- ...?

author: KedasProbe
author_rank: Frequent Contributor
timestamp: July 27, 2015, 04:00:53 pm
content: Quote from: mikron on July 26, 2015, 07:57:48 amNot really relevant here, but the Hameg doesn't have trigger out.(They said it was not possible to get the trigger-out on the Y-out with the current hardware, really a design mistake if you ask me)

author: SeanB
author_rank: Super Contributor
timestamp: July 27, 2015, 04:22:22 pm
content: Quote from: tautech on July 27, 2015, 08:11:08 am59.995 Hz and 49.995Hz, so you can slowly run through a frame line by line looking for things like poor burst levels, rising front and back porch levels ( showing you are not properly doing DC restore somewhere) and noise in your equalising pulses. Just takes a minute or two of watching to see all the frame lines run past, if you do not have a scope with TV line count capability.

author: Rupunzell
author_rank: Frequent Contributor
timestamp: July 27, 2015, 05:39:45 pm
content: Cannot agree with this statement. Best analog scope depends on measurement needs.What makes the 2465 appealing to many are the built in cursors used for measurement, portable form factor and such (I'm one of those who owns a Tek 2467B and turns the most of the display read out information off and uses a 7104 with no readout).In cases where real time band width require goes beyond 400 Mhz with pico-second time delay matching between channels, measuring signals in the microvolt range, high CRT writing speeds, sampling, TDR and other specialize needs any portable analog scope will not do.As for measurement with cursors or DSO data box displays, they can be useful in may cases. In other cases, accuracy and fidelity of the signal display far over rides the instant-precision offered by measurement using cursors or data offered by a DSO data box.Ponder for a moment why Jim Williams continued to use a Tektronix 547 to his very last app note written in a world filled with much fancier, expensive and feature driven time domain instruments.BerniceQuote from: EEVblog on July 26, 2015, 07:53:23 am

author: Howardlong
author_rank: Super Contributor
timestamp: July 27, 2015, 08:23:19 pm
content: Quote from: Rupunzell on July 27, 2015, 05:39:45 pmI have both a 2465B and a 2467B set up in the lab, and until recently the 2467B was the first scope to get switched on when starting a debug session, the quick boot up and finger tip adjustments make it a joy to use compared to many modern day DSOs. The DSO competition available included a Tek TDS2024B, Rigol MSO1074Z-S and an Agilent 54831D, but none of them approached the ease of use and immediacy of the 2465/67B.What changed, why do I no longer jump to the 246xB? After using an Agilent 54622D (see Dave's vid) and finding it a joy to use, but limited at the upper end for what I do, I bought a 54642D 2GSa/s 500MHz MSO. Its super fast boot up time (even faster than the 246xB) and super responsive UI is often easier to use than the 2465/67B. Configuring the delayed trigger on the 2465B sometimes takes a bit of thinking about, this is one area where DSOs often shine compared to CROs.In short, it'd be great to see a video comparing the pros and cons of CROs and DSOs. I am not sure I'd do it justice, but I'd be happy to give it a go if I can show the benefits of a CRO, but I don't think I know what all those benefits of a CRO are by any stretch, so suggestions for comparison would be welcome.

author: nctnico
author_rank: Super Contributor
timestamp: July 27, 2015, 08:27:05 pm
content: I usually use a regular channel on a 4ch scope even if it is just to trigger on. I find it useful to see where the scope is triggering on and then hide the channel once triggering is satisfactory.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 27, 2015, 10:42:42 pm
content: Quote from: SeanB on July 27, 2015, 04:22:22 pmI was thinking about Broadcast standard PAL in Oz----both Mains & Field rate at 50Hz.I don't think Field rate has ever been locked to Mains in this country,but they areveryclose.Mains hum bars on a TV screen take ages to drift down the screen..

author: nctnico
author_rank: Super Contributor
timestamp: July 27, 2015, 11:01:47 pm
content: Mains and broadcast frequencies should have a very close reliation since they are both derived from atomic clocks (AFAIK).

author: Lightages
author_rank: Unknown
timestamp: July 28, 2015, 01:00:38 am
content: I don't understand the concern for no EXT triggering on 4 channel scopes. OK, I can understand some people might be want it but it isn't a big deal. I don't think that the cost of an extra circuit to handle an EXT trigger is worth it. Just my opinion.

author: rs20
author_rank: Super Contributor
timestamp: July 28, 2015, 03:28:09 am
content: Quote from: nctnico on July 27, 2015, 11:01:47 pmIn thelong term, the phase difference between mains frequency and atomic clocks is bounded in some countries. However, the important thing to note is that universally, in theshort-term, the instantaneous mains frequency (/phase) is all over the place, driven by instantaneous supply and demand variations.

author: coppice
author_rank: Super Contributor
timestamp: July 28, 2015, 03:48:25 am
content: Quote from: Lightages on July 28, 2015, 01:00:38 amIf they had a 1000 channel scope, some people would still be complaining about the lack of an external trigger input.

author: dom0
author_rank: Super Contributor
timestamp: July 28, 2015, 06:51:31 am
content: Quote from: rs20 on July 28, 2015, 03:28:09 amlong term ~ a day, at most, usually, in Germany.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: July 28, 2015, 10:53:37 am
content: Quote from: coppice on July 28, 2015, 03:48:25 amWhat do you expect? I mean, the OP complained about the lack of an external trigger input for scopes that actually have such an input

author: MatthewEveritt
author_rank: Unknown
timestamp: July 28, 2015, 12:06:51 pm
content: Quote from: Electro Fan on July 27, 2015, 02:47:02 pmOnly time I've used it is to sync a measurement to the 50Hz hum. Trigger the scope on the mains input, then trigger the (reasonably fast) measurement sweep from the scope's trigger out. Obviously not too precise, but fixes the 50Hz in place so at least you can make like-for-like comparisons more easily.Personally I'd like a separate trigger in, but then I'd like the other 996 channels coppice is promising, and I can't afford them either. If it were a feature I needed I'd pay extra, but I can't justify the expense in general.

author: w2aew
author_rank: Super Contributor
timestamp: July 28, 2015, 06:43:18 pm
content: Quote from: Electro Fan on July 27, 2015, 02:47:02 pmOver the years, I've used Trigger Out to:- drive a counter to totalize the number of "trigger events" over a period of time (such as with an error detector)- drive a trigger input of another instrument such as a logic analyzer, vector signal analyzer, etc. to capture data when the scope is triggered- drive a frequency counter to measure the repetition rate of a signal (low frequency in this case)- trigger a data recorder to capture data around a scope trigger eventetc.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: August 04, 2015, 09:34:57 am
content: To add to the post above:- Adding scope channels or put an analog and digital scope on the same trigger.Basically a trigger-out is much more valuable than a trigger-in because you can sacrifice a channel for a trigger-in, but without trigger-out you are stuck, no way around.