Siglent SDS2000X Plus - Bugs / Missing Features / Feature Requests

[RBBVNL9]

Small addition to the previous email: reading some posts, I now also tried EasyWaveX (current version, 1.1.0.13).

Alas, when I connect the SDS2000X + and in the software select "Send Waveform to AWG", I get the error "Non-Supported Manufacturer or unavailable resource."



 

[TopQuark]

Idea for a feature request, would be nice if the FFT horizontal axis can be displayed in log scale, would make the already powerful FFT capability even more useful imo.

[TopQuark]

Regarding having high pass / low pass with user defined cutoff frequency, it would be extremely helpful if say you need to measure  RMS voltage from specifically 10Hz to 1MHz for obtaining an industry standard noise spec of a circuit.

I am currently building a low noise amplifier for characterizing noise, and have to build in a hardware 4th order filter at the output stage to shape the response of the output. It is 2022, my scope should be able to do that in software.

[HolgerT]

Additionally to the problems and questions described in #624, I've found, that even if set AWG parameters manually to wanted values, these are lost after save -> power-off -> recall. It means recall only restores settings of oscilloscope part of SDS2000X Plus, but not AWG settings.

So my question/request is:
  * to read AWG settings from [wave].csv file, if valid values are there
  * to make it possible to load csv files from internal disk (not usb-drive only)
  * to make it possible to store the wave in AWG/ArbType/Stored-page and recall from it
  * to save/recall all AWG settings by using save/recall button

Thanks and br
Holger

[Fiorenzo]

Someone knows how does the AWG works on this oscilloscope?

Because one hour ago I turned on for the first time this function to make a square wave and a sine wave but if I switch from high impedance to 50ohm nothing happens!
The only thing that changes is the max admitted voltage on the Vpp value box. But the wave stay the same without any change.

Because it's the first time I use a waveform generator maybe I am missing something.

I'm worried about it could have a relay that should switch between the different impedance resistors and it is not working..... It's a brand new oscilloscope.... damn!
Thanks

[Martin72]

Hi Fiorenzo,

Your scope is ok...
To say it simple, you need also a 50ohm load - easiest example, switch input impedance of one channel of the scope to 50ohm...

[2N3055]

Someone knows how does the AWG works on this oscilloscope?

Because one hour ago I turned on for the first time this function to make a square wave and a sine wave but if I switch from high impedance to 50ohm nothing happens!
The only thing that changes is the max admitted voltage on the Vpp value box. But the wave stay the same without any change.

Because it's the first time I use a waveform generator maybe I am missing something.

I'm worried about it could have a relay that should switch between the different impedance resistors and it is not working..... It's a brand new oscilloscope.... damn!
Thanks

Like Martin says, it is  ok.
This one is a little confusing for beginners.
Think of it this way: Generator is always 50Ω. That button is for you to set what kind of LOAD you are using it with.
So if you are using it with 50Ω load or say 1MΩ generator is always doing the same.
But if you are using it with 50Ω, internal 50Ω impedance of the generator and 50Ω will make a divider by 2 so your voltage will be the half of what you get when generator is unloaded (High Z, large impedance connected).
This setting is only a configuration for AWG how it should correctly calculate output voltage it shows you on screen in regards to your load.

[Fiorenzo]

Yeah, you guys are super super super kind
Thank you very much for the explanation.
So it is only a "graphical setting" for the scale...

[Peter_O]

So it is only a "graphical setting" for the scale...

It's not just a graphical setting. The input of the scope does really have an impedance or input resistance of 50 Ohms now. So the source has to deliver a higher current than into an input resistance of 1MOhm. There is a real power P=U*I or P=U²/50 Ohms the input of the scope has to handle. That's the reason, the input voltage is limited when in 50Ohm mode.

[RBBVNL9]

It's not just a graphical setting.

Well, yes and no.

The OP asked about the 50Ω setting in the AWG. This is located at setting "AWG > Setting > Output Load" (and can be set to 50Ω of High-Z). There, it is purely a graphical setting. The output impedance of the AWG is always 50Ω, and the setting in question simply makes sure that *if* you load it with an actual 50Ω load then the scope shows the output voltage appearing over that load. So it's only about values being shown on the screen, no difference in the physical world.

The 50Ω setting for channels (which was not the actual question of the OP) is located at setting "Channel X > Impedance" (and can be set to 50Ω) actually changes something in the physical world. When 50Ω is selected, the oscilloscope activates a relay that puts a 50Ω resistor across the input channel in question. Great feature, but be careful: if you connect a signal greater than approx 7V DC or AC_rms to that channel, you will burn that resistor and thus damage the oscilloscope, with an expensive repair as a result. I have seen quite some broken scopes for this very reason.

You may want to look at the extensive overview I posted at rudiselectronicslab.com , where the above and many other things are covered, or the series of videos I made on this scope.

Best, Rudi

[bdunham7]

if you connect a signal greater than approx 7V DC or AC_rms to that channel, you will burn that resistor and thus damage the oscilloscope, with an expensive repair as a result. I have seen quite some broken scopes for this very reason.

And since this is the "Bugs / Missing Features / Feature Requests thread, I'd call again for Siglent to 'fix' this by monitoring and automatically disconnecting the 50R input when the signal level gets too high.

[mawyatt]

........ by monitoring and automatically disconnecting the 50R input when the signal level gets too high.

Think the old Tektronix analog scopes did this.

Best,

[bdunham7]

Think the old Tektronix analog scopes did this.

Yes, the Tek 24xx series manages to do this just fine, not sure about other models.  It seems an obvious feature to add and it doesn't require anything extra in the signal path.

[tautech]

It seems an obvious feature to add and it doesn't require anything extra in the signal path.

Yes, you would think so.
This exact topic has been under deep discussion the last few days on the Siglent forum.
Can't yet say what will be implemented in the X Plus.

[nctnico]

if you connect a signal greater than approx 7V DC or AC_rms to that channel, you will burn that resistor and thus damage the oscilloscope, with an expensive repair as a result. I have seen quite some broken scopes for this very reason.

And since this is the "Bugs / Missing Features / Feature Requests thread, I'd call again for Siglent to 'fix' this by monitoring and automatically disconnecting the 50R input when the signal level gets too high.

Define 'too high'. You can't just add a comparator or so that looks at the voltage level. It would need a circuit that monitors power dissipation over time instead of just a voltage level. At some point I've fed pulses into a DSO for which I needed the 20V/div range in 50 OHm mode in order for the signal to fit on the screen vertically.

[bdunham7]

Define 'too high'. You can't just add a comparator or so that looks at the voltage level. It would need a circuit that monitors power dissipation over time instead of just a voltage level. At some point I've fed pulses into a DSO for which I needed the 20V/div range in 50 OHm mode in order for the signal to fit on the screen vertically.

"Too high" = enough to damage the resistor.  The exact method is up to them, but since this issue has presumably been solved satisfactorily by others, I'm sure they can figure something out.  There probably are limits to what the hardware can accomplish and we'd have to live with those.

[rf-loop]

if you connect a signal greater than approx 7V DC or AC_rms to that channel, you will burn that resistor and thus damage the oscilloscope, with an expensive repair as a result. I have seen quite some broken scopes for this very reason.

And since this is the "Bugs / Missing Features / Feature Requests thread, I'd call again for Siglent to 'fix' this by monitoring and automatically disconnecting the 50R input when the signal level gets too high.

Define 'too high'. You can't just add a comparator or so that looks at the voltage level. It would need a circuit that monitors power dissipation over time instead of just a voltage level. At some point I've fed pulses into a DSO for which I needed the 20V/div range in 50 OHm mode in order for the signal to fit on the screen vertically.

This  is one important point.

Now in some Siglent models what have internal 50ohm load resistor before normal Hi-Z amplifier/attenuator, display vertical sensitivity is limited to max 1V/div. It do not protect anything but limits usability strongly. If it "protect" something, it only happen in human (user) mind but nothing inside oscilloscope - this "protection" effect I do not believe so much.

After 50ohm parallel load resistor there is nothing to protect but just exactly normal oscilloscope 1Mohm /xx pF input.

So this 50ohm load resistor(s) is component what is first in circuit and important to protect (of course also other things if want dive more deep to these things)
SDS models what have internal 50 ohm and what can also set for DC50 ohm or AC50 ohm (not all models where is 50ohm input available) need note that DC connected 50ohm load is before DC block. DC block (AC coupling) is there in 1Mohm input circuit after 50 ohm load. So 50ohm input is  DC coupled to GND, independent of AC or DC selection, if AC selection is available.

If think this 50 ohm load and signal what it can handle it also good to look some common basics

https://www.vishay.com/docs/48516/_ms9702509-2003-vishaychecklistpulseload.pdf

It also depends highly about what resistors there are used and also what kind of drift we can accept in long time use or even due to single overload peak  (Also resistors manufacturing quality and also front end PCB thermal design are important factors).

But it is extremely clear it do not fail if I have just one simple example:

24V positive pulses. Pulse width is 50ns and whole cycle is 5us  (200kHz 50ns pulses from 0 to 24V)

Cycle power 5000ns,  and and long time average is 0.115W
Peak power(50ns) is 11.5W
Peak V is 24V 
Peak I is 480mA

And now I think what ever resistor there is used...  it do not break with this.
I believe it last well and without even long time meaningful drift or damage risk in practical user cases.

But user can not look this simple pulse with SDS oscilloscope using internal 50ohm... displayed full vertical is 8V with 1V/div.
This limit do not protect any single thing but rejects usability. It only torture users.


Also can calculate with more extreme cases...
But also then need be careful, user can not know this 50ohm load resistor type, thermal dynamics and failure/permanet drift characteristics.


Naturally one good solution is external direct feed thru or attenuating terminator  what can handle more power and if fails no need repair scope and with it, full V/div range can use. 

[Martin72]

Naturally one good solution is external direct feed thru or attenuating terminator  what can handle more power and if fails no need repair scope and with it, full V/div range can use.

That´s what we at work are doing, at least after the third expemsive repair because of the blowing internal resistor. 
We do this, when we KNOW it could be critical and/or when we DON´T know it could be critical..

[bdunham7]

But user can not look this simple pulse with SDS oscilloscope using internal 50ohm... displayed full vertical is 8V with 1V/div.
This limit do not protect any single thing but rejects usability. It only torture users.

Since the option of an external 50R feed-through is readily available, any protection system does not have to be overly complicated nor accommodative of all use cases, even reasonable ones.  They could simply leave the 1V/div limitation along with a monitor that disengages the 50R resistor if any portion of the peak exceeds 8V.  If the user needs to measure some taller pulses, the external terminator is used.  As for the AC50R mode, I hadn't considered that--and unfortunately that appears to me to make the problem not fully solvable in software.  I would recommend having an option in the utility menu to disable that mode, and also to have a warning come up whenever you engage it.  AC-coupled 50R doesn't seem all that useful to me.

[rf-loop]

But user can not look this simple pulse with SDS oscilloscope using internal 50ohm... displayed full vertical is 8V with 1V/div.
This limit do not protect any single thing but rejects usability. It only torture users.

Since the option of an external 50R feed-through is readily available, any protection system does not have to be overly complicated nor accommodative of all use cases, even reasonable ones.  They could simply leave the 1V/div limitation along with a monitor that disengages the 50R resistor if any portion of the peak exceeds 8V.  If the user needs to measure some taller pulses, the external terminator is used.  As for the AC50R mode, I hadn't considered that--and unfortunately that appears to me to make the problem not fully solvable in software.  I would recommend having an option in the utility menu to disable that mode, and also to have a warning come up whenever you engage it.  AC-coupled 50R doesn't seem all that useful to me.

But my old real workhorse Tek 2465A DM/CT can handle these bit higher short pulses just hands down without any single problem using 50ohm inputs and if there is overload it nicely turn 50ohm off, no drama, no difficult design. Designed by hardcore well experienced professionals and there V/div setup range is not limited when 50ohm is selected. If there is single reason for limit it, they have done it.
But yes there is overload protection based to 50ohm load resistor temperature measurements what can protect from some mistakes what also professional users sometimes may do.

500mW power is not lot... just 27dBm. And with this Siglent 1V/div limit even this sinewave can not look and it is hardly clipping and producing lot of harmonics. And still it is in acceptable range in specifications.  22dBm is diplay vertical full range. (160mW)
I can not see any other reason for this limit but somehow warn user that signal may be too high for 50ohm. But it do not prevent anything. And also it is like indirect warning to user then when he meet this situation and start thinking... if he start thinking.

Speccially for models where is not hardware made any overload protection. Much better for this reminder to the user is simple short warning message on screen (in these some situations where warning is mostly like prevent possible accident, as example when scope boot with 50ohm or example when this current oscilloscope power on period 50ohm is first time selected) The user can acknowledge the reminder, for example, by waving hand or saying yes-yes unless he can wait for clock to take care of it.

[bdunham7]

But my old real workhorse Tek 2465A DM/CT can handle these bit higher short pulses just hands down without any single problem using 50ohm inputs and if there is overload it nicely turn 50ohm off, no drama, no difficult design. Designed by hardcore well experienced professionals and there V/div setup range is not limited when 50ohm is selected. If there is single reason for limit it, they have done it.

Yes, that's why I had hoped that protection would be included with the 50R input feature.  But the Tek solution was implemented in (mostly) hardware as part of a very expensive instrument.  The thrifting required to put out a scope with the features of the SDS2000X+ series at their price point probably rules out any such luxuries unless they can be implemented in software.  Given the limited choices, I personally would prefer having to occasionally use an external terminator as opposed to occasionally damaging my scope in error.  No need to lament the unavailability of a more elegant solution in budget gear.

[mawyatt]

The Tek 2465 has the 50 ohm termination resistor integrated on the input hybrid substrate (we've repaired these so know the hybrid design), it's very large and likely can dissipate a considerable amount of power.

Tek notes the input 50 ohm DC mode limit of 5VRMS. Also the Tek doesn't have an AC(50) mode I'm aware of (not on 2465), only DC(50) mode.

The AC(50) mode mentioned on the Siglent must place the 50 ohm termination in front of the AC coupling capacitor, if it were behind the coupling cap then the High Pass AC corner would suffer significantly, or the coupling capacitor would have to be much too large.

This raises an interesting situation because the 50 termination is DC coupled and present at the input even tho the input is set to AC coupling mode. One won't be "seeing" the DC on the scope display, but the input signal will still "see" the 50 ohm termination, so the potential for DUT or scope damage is ever present in AC(50) mode.

Tek's solution on the 2465 was to only offer DC(50) and not AC(50), likely for this very reason!!

Best,

[rf-loop]

The Tek 2465 has the 50 ohm termination resistor integrated on the input hybrid substrate (we've repaired these so know the hybrid design), it's very large and likely can dissipate a considerable amount of power.

Tek notes the input 50 ohm DC mode limit of 5VRMS. Also the Tek doesn't have an AC(50) mode I'm aware of (not on 2465), only DC(50) mode.

The AC(50) mode mentioned on the Siglent must place the 50 ohm termination in front of the AC coupling capacitor, if it were behind the coupling cap then the High Pass AC corner would suffer significantly, or the coupling capacitor would have to be much too large.

This raises an interesting situation because the 50 termination is DC coupled and present at the input even tho the input is set to AC coupling mode. One won't be "seeing" the DC on the scope display, but the input signal will still "see" the 50 ohm termination, so the potential for DUT or scope damage is ever present in AC(50) mode.

Tek's solution on the 2465 was to only offer DC(50) and not AC(50), likely for this very reason!!

Best,

To everything you said: Yes.

Siglent many models what have internal 50ohm support only DC 50ohm.

In some models there can select also AC after DC coupled 50ohm. (on screen there read just AC50 and not warning that load is DC coupled)

Example BodePlot set automatically 50ohm to AC mode so it block DC component which could disturb Automatic Level Control (ALC) what is important to maximize BP dynamic range (but also this max dynamic range (if 50 ohm is in use) is limited some dB's with this unnecessary 1V/div limit).

[Performa01]

50 ohms inputs are only available in DC-coupled mode for the SDS6000A.

Just like the 1V/div limit, this is of course no true protection, but it will remind the operator to be extremely cautious.
It might be a good idea to restrict also the 2000 and 5000 series DSOs to DC-coupling in 50 ohms mode - and this would be an easy firmware fix, but this also means to violate the existing specifications. Therefore it will only be done for future devices.

Speaking of input coupling: like any modern design, AC-coupling does not change the input path significantly. The thinking of a capacitor in series to the input is outdated for these designs. Try to measure the DC-input resistance with a DMM in AC coupled mode. For those too lazy to do that: it is still 1 meg ohm.

It is very true that there is no cheap solution for a 50 ohms input protection, especially not in high bandwidth instruments. Quite obviously, the existing hardware cannot measure the input voltage. For example, how do you detect that the input exceeds 5 Vrms when using e.g. 10 mV/div vertical gain, where the ADC is overdriven at 100mVpp already? So we would need extra hardware for that, which not only costs money, but also leads to the next problem...

Those who use 50 ohms mode regularly, will most likely be concerned about the input return loss and accordingly the standing wave ratio (VSWR). By convention, it shall never exceed 1.5 over the full bandwidth. This cannot be accomplished by just using a relay to connect a termination resistor across the input without further measures. At least we also need to get rid of the (designed in) input capacitance. I suspect this might be one of the reasons, why we cannot use the (frequency compensated) attenuators in 50 ohms mode, hence the 1V/div limit has pure technical reasons as well. Any voltage detection circuit directly at the input, i.e. before the input buffer, will affect the input impedance and degrade instrument performance. As a consequence, this is only feasible if the bandwidth is not too high and money is no object. We simply cannot compare a highend scope of the good old days (with only 400 MHz bandwidth) to instruments that are significantly lower cost and/or higher bandwidth.

For the reasons given above, the cheap SDS2000X Plus of all things has no protection. The SDS2000X HD on the other hand, will have thermal monitoring of the termination resistors. This will not be an absolute protection, yet should be sufficient as long as you don't connect the instrument to high voltage high energy sources.

As we are at it: The solution to overcome the 1V/div limit is of course the use of external attenuators. Anyone dealing with 50 ohms systems should have a rich assortment of these.

An external pass-through terminator on the other hand, can never be a substitute for the internal 50 ohms termination. Because the input capacitance is still present, external trough-terminators are only acceptable up to about 100 MHz.

[bdunham7]

It might be a good idea to restrict also the 2000 and 5000 series DSOs to DC-coupling in 50 ohms mode - and this would be an easy firmware fix, but this also means to violate the existing specifications. Therefore it will only be done for future devices.

It is very true that there is no cheap solution for a 50 ohms input protection, especially not in high bandwidth instruments. Quite obviously, the existing hardware cannot measure the input voltage. For example, how do you detect that the input exceeds 5 Vrms when using e.g. 10 mV/div vertical gain, where the ADC is overdriven at 100mVpp already? So we would need extra hardware for that, which not only costs money, but also leads to the next problem...

I would only expect a fix improvement that is achievable thru firmware with existing hardware.  All of your issues are resolved if you just allow for two mode settings in the utility menu--SAFE and EXPERT or whatever.  In the SAFE mode the 50R terminator disconnects whenever the input is overloaded (even at the lower ranges) and AC50R is disabled.  EXPERT just gives you a warning and leaves you to fry your scope at will.  Or maybe even have a LOCK setting where you need a password to access the 50R menu...