A possibly dumb Q on digital oscilloscopes

[nctnico]

Personally I avoid oscilloscopes from Owon, Hantek, Rigol and Siglent. Too much hit&run strategies going on. That doesn't mean all Asian companies are like that. MicSig and GW Instek for example make true on the promised features.

[peter-h]

Having just spent a few hours reading EEVBLOG I am homing in on the    GW INSTEK GDS-2304A.

The only other candidate is the R&S scope which costs about 2x as much.

Neither comes with bundled-anything and no special offers I can see.

I guess the two are very similar except that the Instek is 8-bit and the R&S is 10-bit. I do need SPI decoding for 8 16 and 24 bit packets and it has to work properly.

[JPortici]

GDS-2000A and E (and MSOs) have free decoders, you just have to download them from the website (no idea why they are not included in the first pace)

but apparently the 2000A can only decode on the LA channels?? 

GDS-2000A CAN/LIN bus analysis software for DS2-08LA or DS2-16LA option

[peter-h]

That presumably avoids a user interface item for setting the signal threshold on the analog traces...

[tautech]

Are these Chinese scopes of reasonable quality, mechanically (quality of switches etc)?

Encoders seem to be the most questioned but it's mostly if the manufacturer used detented ones or not. If the encoder algorithm has been poorly implemented then a detented version is the workaround that many resort to.
Before replacement was common a knob swap using a larger knob for better feel was often used.

Unfortunately I really struggle to see the difference between these various Chinese scopes e.g. the above Rigol and the Siglent SDS2304X which is much cheaper.

Then you need to keep looking, not take only just the opinions of a minority few that have some axe to grind.

Then I read this forum and see so many reports of functions in all of these scopes which simply don't work. Plus reports of poor response (e.g. slow cursor movement) which the Tek and Keysight scopes do properly.

Remember that yesterdays deficiencies that have made it into print have mostly been addressed in firmware revisions by most brands. Check a manufacturers firmware page for the history and frequency of FW updates to get some good idea how mature the product might be.

It would be easy for a nice digital scope user to buy one of these and after a year discover that some feature (e.g. SPI decoding) doesn't work and then it's out of warranty.

All features on the SDS2304X work as expected. The warranty is 3 years.

Plenty of threads about most of these scopes being unable to decode serial data which is off-screen which I agree is almost totally useless.

Manufacturers implement feature in different ways and not all implementations suit everybody. Does it mean you can't get in info/measurement you need...........no it doesn't.
For an overview:


All the rest you need to know about how Siglent's display Decoding is in this post:
https://www.eevblog.com/forum/testgear/choosing-200-300mhz-4-channel-logic-and-canlin-analyser-budget-$2000-$2600/msg1156185/#msg1156185

[peter-h]

Many thanks.

Are there any scopes which can decode 24-bit SPI into a 24-bit integer?

[nctnico]

GW Instek GDS2000E series (and presumably the derived MSO2000 series) can decode SPI from 4 to 32 bits (number of bits freely selectable) and it doesn't decode only what is on screen but the entire memory.

[peter-h]

That's really useful - many thanks.

Are there some "old" HP (Agilent/Keysight) scopes which tick these boxes and which are worth searching for on the used market? These would be very pricey today if you want logic inputs and serial data decoding. However I have used a lot of HP gear over the decades and it is really well built and mostly works very nicely.

A couple of years ago I bought a Marconi 2024 signal generator and an Anritsu 2661G for 2k the lot. This is perfectly usable stuff, if rather old now. OTOH if any of this stuff breaks it can easily be uneconomical or impossible to repair, so you need to get it cheap.

[tggzzz]

That's really useful - many thanks.

Are there some "old" HP (Agilent/Keysight) scopes which tick these boxes and which are worth searching for on the used market? These would be very pricey today if you want logic inputs and serial data decoding. However I have used a lot of HP gear over the decades and it is really well built and mostly works very nicely.

A couple of years ago I bought a Marconi 2024 signal generator and an Anritsu 2661G for 2k the lot. This is perfectly usable stuff, if rather old now. OTOH if any of this stuff breaks it can easily be uneconomical or impossible to repair, so you need to get it cheap.

Be aware that digitising scopes have been improving rapidly over the past couple of decades. Digitising scopes from a decade or two ago mostly have some significant gotchas for some applications. Hence the spec for each individual type of scope has to be read and the consequences understood!

Principal specs to be aware of include the analogue front-end bandwidth, the single-shot and real-time sampling rates, the depth of the memory buffer, sharing a single ADC between all used inputs, whether post-processing is on the whole memory buffer or just what's visible on the screen, ADC resolution.

[peter-h]

Thanks.

One thing which is missing on older stuff is the amount of buffering - because memory used to be expensive and you need very fast RAM for a logic analyser / digital scope type of application (even if you interleave it). But does one need megabytes of memory in reality? What applications need it?

ISTM that everything out there is 8-bit, except the RTB2000 which is 10-bit but samples at "only" 1.25Gsps.

[nctnico]

Thanks.

One thing which is missing on older stuff is the amount of buffering - because memory used to be expensive and you need very fast RAM for a logic analyser / digital scope type of application (even if you interleave it). But does one need megabytes of memory in reality? What applications need it?

All! It is much easier to capture a trace at a long time/div & high samplerate and zoom in to get more detail without needing to setup complicated trigger settings to catch part of a signal with a higher samplerate (let alone reproduce a rare event). Even better if the oscilloscope has a search function where you can search for anomalies.

[David Hess]

Thanks.

One thing which is missing on older stuff is the amount of buffering - because memory used to be expensive and you need very fast RAM for a logic analyser / digital scope type of application (even if you interleave it). But does one need megabytes of memory in reality? What applications need it?

All! It is much easier to capture a trace at a long time/div & high samplerate and zoom in to get more detail without needing to setup complicated trigger settings to catch part of a signal with a higher samplerate (let alone reproduce a rare event). Even better if the oscilloscope has a search function where you can search for anomalies.

I disagree with this in some respects.  Delayed acquisition capability (delayed sweep) is just as good except where one needs to zoom into the pretrigger record (1) or where only a single acquisition is available.  Searching for anomalies is a job for DPO mode rather than a search function; DPO operation will always catch it but how can you know what an automated search missed?

Long record lengths for zooming replaced delayed acquisition when increasing integration made them a cheaper solution.  Increasing integration also made implementing automated searches of long processing records less expensive than DPO operation.

(1) There actually is a way to implement delayed acquisition with negative time but it was never an important enough feature to bother implementing in a DSO.  Some analog sampling oscilloscopes did it to avoid having to use a delay line or pretrigger signal.

[peter-h]

I have an opportunity to get an ex demo (half price) HP MSOX3034T. It is not clear if this has the 16ch MSO option (SPI etc decoding) but otherwise looks very good.

Are there any known gotchas?

[nctnico]

Thanks.

One thing which is missing on older stuff is the amount of buffering - because memory used to be expensive and you need very fast RAM for a logic analyser / digital scope type of application (even if you interleave it). But does one need megabytes of memory in reality? What applications need it?

All! It is much easier to capture a trace at a long time/div & high samplerate and zoom in to get more detail without needing to setup complicated trigger settings to catch part of a signal with a higher samplerate (let alone reproduce a rare event). Even better if the oscilloscope has a search function where you can search for anomalies.

I disagree with this in some respects.  Delayed acquisition capability (delayed sweep) is just as good except where one needs to zoom into the pretrigger record (1) or where only a single acquisition is available.  Searching for anomalies is a job for DPO mode rather than a search function; DPO operation will always catch it but how can you know what an automated search missed?

DPO mode cannot catch an anomaly 100% because it has blind time (including the operator); only a properly set trigger condition can but that is a different discussion. Search works best in stop mode; it isn't a realtime tool so you can change the search parameters and examine the same data again. When combined with decoding or FFT you can also search for specific messages, data or frequency peaks.

I have an opportunity to get an ex demo (half price) HP MSOX3034T. It is not clear if this has the 16ch MSO option (SPI etc decoding) but otherwise looks very good.

Are there any known gotchas?

Make sure it includes the MSO probe or expect to spend $300 to $400 on the probe. Also check for the options. Dunno if this model can be hacked and/or if you are willing to do that.

[borjam]

Even with their (many!) limitations I wouldn't just discard Chinese oscilloscopes. Honestly, it makes me feel bad to have a Rigol and read those fantastic application notes from Keysight, Tektronix, etc.

An example of how useful (or not) the infamous DS1000Z can be.

Last week a friend was struggling with a simple communications problem: reading information from a device using Modbus. When he asked for help all he could say was "the reading function returns a timeout".

How do you debug that? Of course there are two manufacturers involved and they will probably say "my stuff is fine". So you grab the cheap DS1000Z, make a capture, and you find out all this (warning, not rocket science, pretty obvious!)

- The command is properly sent and understood by the other device. It actually replies. Also, it replied in 25 ms.

- There is a bug in the Modbus library of the device sending the request, it doesn't set the RS485 interface in receive mode after transmitting.

- We better add termination, although the signal is useful better to avoid that ugly overshot (the decoded screenshots were taken after we fitted a couple of resistors)

- And we could even decode a couple of packets in order to check that it really works according to the documentation.

With all the deficiencies, "pluses" and a somewhat provincial software design with subpar interface responsiveness, and surely it helps that this is not exactly rocket science (Modbus at 9600 bps over a 50 m twisted pair), I would say that the 450 euros of the oscilloscope have been more than worthy.

While we would have found out sooner or later, the toy really allowed us to find out pretty soon. Moreover, you can always make a better case with the manufacturer when you can document your findings.

I know there are much better oscilloscopes which are much more expensive. I now that the math functions in my old LeCroy 9400 are much better designed. But what was the price of a 9400 back when it was launched?

[peter-h]

This is somewhat off-topic but I do a lot of Modbus stuff and one could have found your issue with any DSO, no matter how cheap or slow. In fact one could have done it with an analog scope, if one could retransmit the Master request over and over.

Being able to decode NRZ (RS232/422/485) data would save a fair bit of time...

The 25ms response delay is common; I have seen up to 1 second if doing a block request. The main reason is that the people who develop the software in many Modbus slave devices are using C++ and "if in doubt use a float" and "if your code is so crappy that you are getting underflow then use a double" and right away you are looking at several ms just for a division, if using some cheap CPU.

FWIW, I have a good selection of old HP and Tek kit (back to 1980s) and it is outstanding. I have the service manuals and have repaired some of it. It's clear to me that DSOs are however in a different category, with vastly more complexity and close to zero repairability once something nontrivial goes. That's why ex demo stuff is probably worth looking at. That MSOX3034T lists at about 8k GBP - not sure what the digital input situation is; they all seem to have the front panel header... would they just ship them without the probe??

[Keysight DanielBogdanoff]

Being able to decode NRZ (RS232/422/485) data would save a fair bit of time...

FWIW, I have a good selection of old HP and Tek kit (back to 1980s) and it is outstanding. I have the service manuals and have repaired some of it. It's clear to me that DSOs are however in a different category, with vastly more complexity and close to zero repairability once something nontrivial goes. That's why ex demo stuff is probably worth looking at. That MSOX3034T lists at about 8k GBP - not sure what the digital input situation is; they all seem to have the front panel header... would they just ship them without the probe??

Yes, on the InfiniiVision oscilloscopes that support digital channels (2000 X-Series and up), we do ship DSOs with a populated MSO board, and users can upgrade their DSO to an MSO - they get a license and cables.

Also, repair on new equipment (especially digital scopes) is a whole new monster compared to older analog scopes.

Finally, we do offer UART decoding (RS232, RS422, RS485) on the 2000 X-Series and up scopes:
http://www.keysight.com/en/pd-1951451-pn-DSOX3COMP/computer-serial-triggering-and-analysis-rs232-uart-for-infiniivision-3000-x-series?cc=US&lc=eng

plus some user definable manchester & NRZ trigger and decode:
http://www.keysight.com/en/pd-2796492-pn-DSOXT3NRZ/user-definable-manchester-and-nrz-trigger-and-decode-for-3000t-x-series-oscilloscopes?nid=-32976.1210574&cc=RO&lc=eng

[peter-h]

Thanks Daniel.

The option being mentioned to me is DSOXT3APPBNDL which apparently enables absolutely everything. Does this make sense?

Google seems to suggest it does enable everything.

[Wuerstchenhund]

Searching for anomalies is a job for DPO mode rather than a search function; DPO operation will always catch it but how can you know what an automated search missed?

DPO mode cannot catch an anomaly 100% because it has blind time (including the operator);

This, and it is only really good for repetitive signals.

only a properly set trigger condition can but that is a different discussion. Search works best in stop mode; it isn't a realtime tool

That depends on the scope. Most of the time I search for anomalies I use the scope's analysis tools (like WaveScan or InfiniiScan) in running mode, and that's much more convenient that having to manually go through acquire-stop-search cycles. Also, capturing the timing of glitches over an extended period (I just leave it running and when I come back the scope shows me a list of events with timestamps) often helps a lot to find the source.

[peter-h]

Unfortunately the used MSOX3034T which was on offer has gone, so I am in the market for one, with the digital inputs, and SPI and NRZ (RS232 etc) serial decoding. The ARINC429 decode option would be nice too... Upper limit GBP 4k which I believe is about right for an ex rental (good condition) scope - roughly 1/2 of the new price.

I don't mind if it comes from the USA (I have a DHL account number etc) but then it would need to come from some reputable source.

Rental companies do very well out of equipment sales because they buy the stuff at distributor prices and get a LOT of money on the rental. In a previous life I used to rent test equipment and you paid the new price in 1 year.

[Wuerstchenhund]

Unfortunately the used MSOX3034T which was on offer has gone, so I am in the market for one, with the digital inputs, and SPI and NRZ (RS232 etc) serial decoding. The ARINC429 decode option would be nice too... Upper limit GBP 4k which I believe is about right for an ex rental (good condition) scope - roughly 1/2 of the new price.

There should be plenty of options. If you can live without ARINC then I'd have a look at the LeCroy WaveSurfer 3000. It's a competitor to the DSOX/MSOX3000T but cheaper and offers a bigger screen, more memory (10Mpts vs 4Mpts), better FFT and a wider choice of probes. For Europe LeCroy has currently a some promos where you get all options or MSO for free:

http://teledynelecroy.com/europe/promotions/promotions.aspx

I'd also ask about ex-demo units which are regularly discounted by 40% or more.

You should be able to get a WS3034 with options within your budget.

Rental companies do very well out of equipment sales because they buy the stuff at distributor prices and get a LOT of money on the rental. In a previous life I used to rent test equipment and you paid the new price in 1 year.

True, but just because these companies made a killing through rental fees doesn't mean they necessarily sell of their kit for reasonable prices.

[peter-h]

A WS3034 does look nice; I have emailed them. These are not so commonly seen so I wonder how buggy they are...?

[Wuerstchenhund]

These are not so commonly seen so I wonder how buggy they are...?

I haven't seen any bugs in the current software, there have been a few minor bugs in the initial software version when they came out in 2014 but nothing that would have stopped you working on what you were doing, and they were fixed pretty quickly. LeCroy is a big-name A-brand like Keysight, Tektronix and R&S, and offers very good software support for its scopes. They also generally support their scopes much longer than other manufacturers.

At work we have quite a few of the WS3054 (500MHz variant) and no problems aside from one arriving DOA (was immediately replaced by LeCroy). We don't have any DSOX3k scopes but we have several DSOX/MSOX4104A scopes, but most of our engineers seem to prefer the WS3054 when needing a 500MHz scope (of course if they need more than 500MHz BW in a compact scope then they have little choice). The larger sample memory is one thing (also, the 4Mpts in the DSOX/MSOX halves or quarters depending on what you do, which can leave very little memory available). The WS3000 uses the same UI (MAUI, which was developed for touch interaction from the start) as LeCroy's high end scopes, and they can use the same ProBus active probes (Keysight artificially limits compatibility between probes for Infiniivision like the DSOX3k/4k and Infiniium scopes, which are their highend scopes). And it comes with WaveScan (a tool to find glitches in signals, works even in real-time) and LabNotebook (for documenting measurements).

A few of these scopes are also used on the road (i.e. carried around site to site) and so far the WS3k seems to do very well.

I believe there are a few people in this forum who bought a WS3000 scope, might be worth asking them about their satisfaction with the scope.

[JPortici]

Europe LeCroy has currently a some promos where you get all options or MSO for free:

http://teledynelecroy.com/europe/promotions/promotions.aspx

I'd also ask about ex-demo units which are regularly discounted by 40% or more.

You should be able to get a WS3034 with options within your budget.

holy... why do they send me just marketing crap on emails?

thanks for pointing that out, tomorrow i'm definetly making the boss see that link. exactly one week ago we were talking about getting new equipment

old video but gives a hint at what wavescan is, on the WK3000

[Wuerstchenhund]

holy... why do they send me just marketing crap on emails?

They're not very good at marketing, most of the people that work in sales are engineers. On the upside, they never sank to the level of those silly "ours-vs-theirs" comparative whitepapers marketing pamphlets that especially Keysight and Tek love so much.

thanks for pointing that out, tomorrow i'm definetly making the boss see that link. exactly one week ago we were talking about getting new equipment

Keep the link if you want to see in the future what current promos are there for Europe, the promos change but the link doesn't.

old video but gives a hint at what wavescan is, on the WK3000

   Yes, that's a good video. It shows pretty well how the scope operates.

As you said the video is a bit older, so for anyone watching this be aware that the scope in KF5OBS' video is one that ran on one of the initial software versions back then in 2014. Back then there was no DVM (which came with a later software version and was a free "upgrade" for any WS3k), fewer serial decode standards and the optional AWG was just a signal generator (as DVM, AWG functionality was included in a later firmware, being a free upgrade for anyone who had a WS3k with signal generator option). Since then, besides fixing bugs, the updates brought new functions and other improvements.