A possibly dumb Q on digital oscilloscopes

[capt bullshot]

Yes, the scope will accept the signal from any active (single-ended or differential) or passive probe, as long as you are able to connect the signal and power the probe. Except for some scopes exceeding 1GHz bandwidth, all scopes accept standard BNC plugs and don't care if it's just a cable from a signal generator or an active probe thats needs to be terminated into 50Ohm (as long as the scope has a build in 50Ohm termination that you can turn on, and yes, you can always turn on the 50Ohm termination manually, except the scope doesn't have a 50Ohm termination built in).

[peter-h]

Thank you both.

It thus looks like that the active probes which go right up to the scope panel have a connector which mates inside the BNC "panel socket" but doesn't engage the bayonet.

Otherwise, how does this one work?

[capt bullshot]

This one locks the bayonet by turning that little lever you can see on top. It uses the bayonet, but isn't a real BNC, rather some kind of custom made locking mechanism that fits the BNC connector on the scope.

[hs3]

but a basic one like this



should be usable so long as you work out how to connect the external power to it (looks like a Lemo connector on that one).

This probe has at least offset control interface in the Lemo connector in addition to the various supply voltages. But can be used with external supply.

[nctnico]

I think it is better to go for more universal probes so you are not getting into a vendor lock-in. OTOH the vendor specific probes allow things like offset to be controlled from the scope's user interface and so on.

[alm]

If you want high performance (e.g. bandwidth beyond a few GHz, high-sensitivity DC current probes, high-sensitivity differential probes), you are mostly limited to Tek/Keysight/Lecroy, which for the more recent probes means vendor-specific interfaces. Scope vendors know this, and treat probe technology as a unique selling point.

[peter-h]

I have got a better price now for the WS3024 from Le Croy here in the UK, after I told him the USA is a lot cheaper. Still inflated though.

I wonder if the function gen is truly worthless... you can get one of these https://www.rigol-uk.co.uk/Rigol-DG1032Z-Waveform-Generator-p/dg1032z.htm for less!

[Wuerstchenhund]

I have got a better price now for the WS3024 from Le Croy here in the UK, after I told him the USA is a lot cheaper. Still inflated though.

Of course it's cheaper in the US, that has always been the case for pretty much anything.

But now you also pay for the fact that the UK recently decided to commit economical suicide (Brexit), which is reflected in the large price increases of foreign-made goods. But hey, people voted for it, so it's OK.

I wonder if the function gen is truly worthless... you can get one of these https://www.rigol-uk.co.uk/Rigol-DG1032Z-Waveform-Generator-p/dg1032z.htm for less!

The built-in AWG that can be found in many scopes isn't worthless, it's just not a very attractive offer if you actually have to pay full price for it because you can get an external AWG with better specs for the same or even less money. That might be different if the AWG option is thrown in as part of a deal, though.

[JPortici]

in the end, we also received a perplexing quote from lecroy
next week they're coming for a test drive, leave us a scope for some time.
 I hope to get the quote from keysight in time so we can compare notes and have a little chat..

[peter-h]

"But now you also pay for the fact that the UK recently decided to commit economical suicide (Brexit), which is reflected in the large price increases of foreign-made goods. But hey, people voted for it, so it's OK."

You might be surprised... after the fall in the value of GBP, my company's export sales went up 3x, which is worth way more than paying a bit more for the imported parts. I voted for Brexit, along with almost every other owner of a small business which actually makes something, and had to deal with the increasing EU regulation like the ROHS, ROHS2, REACH, etc nonsense. The national media in the rest of Europe of course likes to portray the vote as one solely by stupid bigoted xenophobic people, which is quite funny since several other countries would leave the EU tomorrow if they got a free vote 2 sides to every coin... Electronics design engineers love the EU because it forces a lot of obsolescence and keeps them in jobs Many others love the EU too - basically the whole of the research community and especially academia - because they live off the grants.

Only some things are cheaper in the USA. Normally the manufacturers align the pricing, to prevent people bypassing exclusivity agreements. In this case it is surprising how much difference there is. Not just in the published item prices (perhaps 20%) but in the much bigger value of the bundled discounts which in Europe are quoted under the table.

[nctnico]

with the increasing EU regulation like the ROHS, ROHS2, REACH, etc nonsense.

Sidenote: I don't see how preventing toxic materials from entering the food supply chain is a bad thing. There is more to doing business than making money. Unfortunately companies will only do the morally right thing when they really have to. Also if your business' profitability strongly depends on the value of the currency then there is something fundamentally wrong with it because it can go any direction.

[peter-h]

AFAIK there was never any evidence that metals from scrapped electronic equipment enter the food chain. Most of the toxic stuff gets there from other sources.

The gross profit margin in most manufacturing is about 75% of the selling price (e.g. if you sell a scope for 1k then the parts need to be 0.25k max) and this is not very vulnerable to currency moves. What is vulnerable (in both directions) to a small shift in price is the quantity sold.

[nctnico]

AFAIK there was never any evidence that metals from scrapped electronic equipment enter the food chain. Most of the toxic stuff gets there from other sources.

It is not just about the electronics scrap but also about manufacturing of goods using toxic substances. Google 'China lead poisoning' for example and you'll see the problem. If there is no market for products with toxic materials then the toxic materials won't be used. But these things don't always happen far from your own front door. Over here in the NL we currently have a problem with a factory producing Teflon which has been dumping toxic waste in the surface water. This has lead to contamination of the drinking water.

[Hydron]

I don't think we'll see a lot of the standards and regulations changing much. As an example when I designed and tested stuff in NZ (i.e. part of the former glorious empire) we followed a lot of EU standards (renamed as "AS/NZS" standards), despite the governments not being forced to use them. While we were not required to conform to ROHS etc for local sales we did anyway as the contract manufacturers were set up to do it, and it allowed us to CE certify our products for sale overseas.

That said, I hate lead free for DIY and repairs, and I'm not convinced that there wasn't an element of European trade protection in implementing ROHS requirements.

[Someone]

What I am getting at is that the scope can't be insisting on EEPROM identification (like inkjet cartridges etc) IF it accepts PASSIVE probes with its 50 ohm input mode. An old style active probe will look just like a passive probe.

Not entirely true, manufacturers can and do lock out probes they don't want used:
https://www.eevblog.com/forum/testgear/1159a-differential-probe-modupdate/
So you need to sever the identification link (eeprom and/or resistor strapping) before the probe is fully dumb and can be used.

[peter-h]

If I understand it correctly, that thread on the Agilent 1159A shows a probe which doesn't just have a simple BNC output, plus a separate power lead. I can't find good images on google but it seems to make a connection to the BNC plus some other connections next to it.

I can completely see such a probe is not going to be back-supported.

But any probe which has a simple BNC output plus a separate power cable should work with any scope.

The offset adjustment can't be a big issue. One has to move traces up and down when using a scope anyway...

Hydron - I agree with you; not much will change for big companies, or companies which export to customers who are picky (basically large companies who demand the declarations signed in blood and with a DNA specimen attached ). But there is a more subtle and beneficial effect: IF you can sell non EU-compliant products in the home market, that undermines the automatic "everything has to be compliant" presumption, which undermines surveillance and enforcement and allows small companies to start up and grow. Just like Ebay and Amazon facilitate currently (you can sell anything there, with no questions asked) except they are not really suitable for B2B stuff. I started in electronic mfg in 1978 and back then you could have a small business selling B2B. Today, the entire consumer market is off limits to small players and there are just small niches left in B2B, which makes it really hard to start a business in electronics (and much else).

[David Hess]

The offset adjustment can't be a big issue. One has to move traces up and down when using a scope anyway...

That is not what offset adjustment is for.

Passive low impedance probes may implement offset so the input current can be adjusted to zero at input voltages other than ground.  This prevents the low impedance of the passive probe from upsetting the operating point of the circuit and allows more accurate voltage measurements.

Active probes use offset to shift their limited input voltage range to bracket the signal which is important for them because they have horrible overload recovery.  Sampling inputs also support this but since they are immune to overload, they use it to allow higher sensitivity measurements of large signals like the 7A13.  See below.

Oscilloscope inputs use offset so that their high sensitivity ranges can be used to make measurements at large DC offsets.  In the case of the Tektronix 7A13, this is like having a position control which operates over 20,000 divisions; at 1mV/div, it can make measurements over a +/- 10 volt range.  Many DSOs support separate position and offset controls although usually not such an extreme offset range.

[peter-h]

That sounds like there must be a D-A converter inside the probe, whose output drives the ground of the input amp, and a level shifter circuit to bring it back down to the output to the scope which obviously has to be power ground referenced. And some user interface in the scope for setting the D-A output.

[alm]

Or just an analog voltage generated by the scope (DAC or even a potentiometer). This is how it worked in older probes. Some probe power supplies have pots for offset adjustment.

[peter-h]

Is the LeCroy WS3024 (200MHz) with the 350MHz software key applied *exactly* the same as the 3034, including all accessories?

I know this is a bit silly but presumably the front label  says "200MHz", or does the upgrade come with a sticker?

Also, since this seems to be the 500MHz model anyway, how are the bandwidth degradations implemented? I might go for the 200MHz model because it is so much cheaper...

Also this scope supports ETS and does that work with a 200MHz or 500MHz analog input amp? I would be amazed if they have analog switches which switch in some capacitors to slow down the front end amp!

[JPortici]

I Have the lecroy rep coming in a few hours with a 3024 I may ask some questions

[peter-h]

You could ask him what is the best he can do with the MSO (16 logic inputs) and EMB (SPI etc) options

[Wuerstchenhund]

Is the LeCroy WS3024 (200MHz) with the 350MHz software key applied *exactly* the same as the 3034, including all accessories?

Yes. The hardware is identical for I believe up to 500MHz.

I know this is a bit silly but presumably the front label  says "200MHz", or does the upgrade come with a sticker?

Not silly at all, and yes, BW upgrades should come with a new set of stickers.

Also, since this seems to be the 500MHz model anyway, how are the bandwidth degradations implemented?

The steps are 200MHz - 350MHz - 500MHz - 750MHz (and 1Ghz for the Siglent variant but not for the LeCroy), as I said as far as I remember the hardware up to 500Mhz is all the same, the 750Mhz variant has a different front-end (so needs to go back to LeCroy for upgrade).

Also this scope supports ETS and does that work with a 200MHz or 500MHz analog input amp? I would be amazed if they have analog switches which switch in some capacitors to slow down the front end amp!

Not sure what you're saying. ETS works with any signal that lies within the voltage levels and BW limits of the scope (although if its useful is a different question).

[peter-h]

The exact way that ETS works (or doesn't) will be dependent on the front end, before the ADC.

Let's say for example that the bandwidth crippling is implemented with a lowpass filter on the waveform displayed on the LCD i.e. wholly in software. That would be the easiest (and the most cynical) way to do it. It would be very easy to do because it doesn't matter whether it takes 10ms or 50ms to draw the picture on the LCD.

But if they actually modify the BW of the input amp that will affect ETS too because the waveform is already BW-crippled.

What I am getting at is that a 70MHz scope which is actually 500MHz might be giving you 500MHz with ETS i.e. when looking at any repetitive waveform. Only with single shot signals it will be BW limited to 70MHz.

[Wuerstchenhund]

The exact way that ETS works (or doesn't) will be dependent on the front end, before the ADC.

Err, no. ETS is a sampling mode, and if it works depends on the characteristics of the input signal.

Let's say for example that the bandwidth crippling is implemented with a lowpass filter on the waveform displayed on the LCD i.e. wholly in software. That would be the easiest (and the most cynical) way to do it. It would be very easy to do because it doesn't matter whether it takes 10ms or 50ms to draw the picture on the LCD.

It wouldn't be very easy, it would require a real-time fourier transformation, stepped removal of the excess frequency components, and then a real-time inverse FT to get the waveform back. Even on a high end scope with powerful processing this won't result in very good update rates. And it would be a silly way to do this as limiting BW in hardware is much easier, especially when considering that better DSOs already use DSPs to get the required linearity from their front ends.

But if they actually modify the BW of the input amp that will affect ETS too because the waveform is already BW-crippled.

Not sure what you're getting at. The analog BW is what it is, independent of the sampling mode (of which ETS is only one).
If you buy a 200Mhz scope then changing the sampling mode will not get you more BW¹.

What I am getting at is that a 70MHz scope which is actually 500MHz might be giving you 500MHz with ETS i.e. when looking at any repetitive waveform. Only with single shot signals it will be BW limited to 70MHz.

Such a scope doesn't exist. As stated before, ETS is a sampling mode and doesn't affect the analog BW which is determined by the scope's front-end and which is generally static.

Also, I get the impression you underestimate the requirements for ETS to be actually useful. Most waveforms people consider as "repetitive" actually aren't truly repetitive.


¹  It appears that some of HP's old Infiniium 54800 Series scopes show a slightly increased BW in ETS mode than in normal sampling mode, probably caused through different parameters feed into the scope's DSPs. But these are exceptions.