R&S NGE100 voltage jumping around

[Fixpoint]

Fixpoint, we bought this PSU as replacement for the old analog Hameg 3ch PSUs. As such it was presented to us by R&S when we visited them. Whatever my coworker was trying to do, he searched for an error in his circuit awhile before pinning it down to the new PSU and throwing it back to me. Hes is using the old one again.
And I don't know why a properly built PSU should jump 30mV around at 4V constantly, even when mains is unstable (which is not, of course). I just needed to know if others have the same flaws, seems not, so I will send it back!
I would overlook this when it would be a cheap aliexpress PSU but not for a >1000€ unit.

Honestly, I have to wonder what you and your coworkers are doing.

(a)  It sounds that you are doing precision stuff but are using a device that is officially not meant for precision stuff (just have a look at the specs). R&S marketing material clearly states that the device is primarily aimed at the educational sector, i. e. schools and universities, and that ROBUSTNESS is its primary feature, NOT accuracy (they say that it will "survive generations of students").

(b) You are complaining that the device does not satisfy an *unspecified* specification, and god knows what your conditions of your measurements were. R&S "only" talks about a specific frequency range? Yes, because that's the industry standard for PSU specs ... I think that's ok.

I would never argue with "a 1000 EUR device must do this or that, even if unspecified". Well ... that may be your opinion, but it will only buy you frustration. The price has nothing to do with anything. If you have SPECIFIC requirements, you must look for EXACTLY the right equipment and ask for the numbers. Yes, the price is a number, but ... the wrong one. 

BTW, just for the sake of completeness, I also made a few measurements some weeks ago. Just ballpark, of course. https://www.eevblog.com/forum/testgear/seeking-psu-advice-rohde-schwarz-nge103b-com3-or-keysight-e36313a/msg3231192/#msg3231192

[RBBVNL9]

The previous email stresses we should look carefully at what the manufacturers actually specify, claim or say. A few comments on that in the context of this NGE PSU...

(they say that it will "survive generations of students").

To know what 'it' means in the above sentence, we need to look at the R&S brochure. That says "The design of the connectors is robust enough to survive generations of students." So this statement is specifically about the output (banana) connectors of the device. I hope this high robustness level also holds for all other parts, but that is not what they claim.

Just talking "specified" and "unspecified"  ;-)

R&S marketing material clearly states that the device is primarily aimed at the educational sector, i. e. schools and universities

This may be your interpretation, but I do not see that written in the market material - at least not the R&S data sheet / brochure for this device (from which you seem to have taken the above statement). There it says "Tailored to be used in education, labs and system racks". (They use this sentence 3 times). So I see three applications listed, including 'labs'. And to be sure, that same word 'labs' is used in the marketing material for the more expensive R&S series like the HMP, HM, NGP and NGP series.

If you have SPECIFIC requirements, you must look for EXACTLY the right equipment [...]

Finally, I agree that if specifications are provided, then we should look at them (and judge on them). Still, I feel a bit uncomfortable that no later than the second sentence in the NGE product procure reads "They offer high efficiency combined with low ripple [...].". That may be a bit misleading for an PSU who's ripple specification (and actual performance) seems considerably below (meaning 'worse than') that of comparable devices.

(I admit we can have a discussion on what 'comparable' means. With N=1 let me just mention the Keysight E36300 Series that specifies voltage ripple and noise of "< 350 uVrms/ 2 mVpp" compared to "typ. < 1.5 mV (RMS), < 20 mV (peak-to-peak) (meas.)" for the NGE.)

[Fixpoint]

This may be your interpretation, but I do not see that written in the market material - at least not the R&S data sheet / brochure for this device (from which you seem to have taken the above statement). There it says "Tailored to be used in education, labs and system racks". (They use this sentence 3 times). So I see three applications listed, including 'labs'. And to be sure, that same word 'labs' is used in the marketing material for the more expensive R&S series like the HMP, HM, NGP and NGP series.

Come on, when we see education listed first, we know what we are dealing with. Marketing will always name the primary use case first. And OF COURSE they mention labs. I mean -- where else do you use a bench power supply? Definitely not on the road. The mention of labs and system racks is self-evident and just marketing speak because it would be a bad idea to mention ONLY education. They want to make money, of course they also mention other uses. Why not use it in a lab? Sure, it works, that's not a wrong statement, and for many labs it will do a great job. It's just not the *primary* use case.

BTW, the RTB2004 is also designed with education in mind. They even have a special education offer.

Finally, I agree that if specifications are provided, then we should look at them (and judge on them). Still, I feel a bit uncomfortable that no later than the second sentence in the NGE product procure reads "They offer high efficiency combined with low ripple [...].". That may be a bit misleading for an PSU who's ripple specification (and actual performance) seems considerably below (meaning 'worse than') that of comparable devices.

Again, marketing speak ... Of course they will say "low ripple", just because it doesn't have high ripple. Which is true, it doesn't. Please let's remember that the NGE is not a bad instrument. And let's be reasonable -- the NGE indeed has low ripple, just not VERY low ripple. There are many PSUs that don't have low ripple, with those you have pretty different numbers than with the NGE.

[RBBVNL9]

Whatever reasons R&S have to write that this device is "Tailored to be used in education, labs and system racks", if they do so, we cannot disqualify someone for using it in a lab.

I agree we cannot expect unusually high performance from an instrument when this is not specified. But that does not mean that ‘anything goes’ for a device that is marketed for use in a lab. If justanothername’s unit is indeed jumps up and down by 30 to 40mV, is that OK? And, just suppose, that the jumps are 100mV, would that be OK? Of a full volt jump, is that OK, even when this performance criteria is not specified?

I’m not saying I have the wisdom of saying when something is still OK and when it is not, but I cannot blame someone for bringing up the question, or wanting to know whether his of her own unit behaves differently from that of others.

[switchabl]

Without weighing in on the more general discussion: I am not sure that fluctuations <20Hz are completely unspecified. I would think they should not exceed the "programming accuracy" of < 0.1% + 30mV.

[RBBVNL9]

Oh, wait a moment! All this time, we have all been writing that this voltage stability aspect was not specified for this device.

But I think that R&S actually DOES specify this!!! Look at the data sheet, page 8:

Programming accuracy:
Voltage.   ± (% of output + offset).  < 0.1% + 30 mV


So at 4V output, the output should be within 34 mV from the set value (correct me if I am wrong).

If so (and assuming his measurements are OK) then justanothername's unit is on the edge of the specs, perhaps just under, perhaps just above.

In the specs, no load condition is indicated, but I think it is reasonable to assume that this specification must be met under load. Would be interested to see this.


PS: The data sheet programming accuracy for current, and also specifies the read back accuracy. I also noted that all specs are valid at +23°C (–3°C/+ 7°C) after 30 minutes warm-up time. There is also a lot more small print one might want to read to understand what these specifications mean.

[RBBVNL9]

@switchabl: our posts crossed in cyberspace ;-)

[RBBVNL9]

Repeating the above specs: at 4V output, the output should be within 34 mV from the set value (correct me if I am wrong). So, the output may 'slowly' fluctuate up to 68 mV, if that fluctuation is precisely around the set value. (Fast fluctuations are covered by the stricter ripple and noise specs that apply from 20Hz on.)

Just just measured my NGE at 4V with a 2.5A load, out of curiosity. A did a 1 hour, 1 second interval output voltage measurement (using the setup I discussed above). Let us for the sake of the argument suppose this measurement is accurate (do not want to go down this road)... My measurements varied from 37.5mV below the set value to 2.9mV below the set value. (It never goes up to or above the set value.) My results would be about same as the allowed deviation, or a bit above (assuming they are valid for a device under such load).

The graphs I see suggest that some kind of switching is going on (some minutes high values, then some minutes low values, and so on).

But again, I am not claiming my measurements are in fact accurate. And if they were, we would still need to look at all the fine print in the data sheet...

[switchabl]

It is not stated explicitly (as far as I can see), but I would assume that the programming accuracy is specified with no load. So you would have to allow for another 0.1%+20mV due to load regulation.

(At least for the older Agilent power supplies, I remember that the performance verification procedure had you checking the programming accuracy with no load, and then verify load regulation separately.)

Overall, the specs of the NGE100 don't look too impressive to me. I don't think I would want one as my go-to bench supply for design work (especially analog). It is definitely not in the same league as the more expensive Keysight E36300 or R&S HMP series (or an old Agilent E363x at that).
That being said, for many applications it will still be more than good enough and it packs 3 independent channels with a decent amount of power in a compact box. If you qualify for an education discount the price might be quite attractive as well.

[Fixpoint]

Overall, the specs of the NGE100 don't look too impressive to me.

Yes, that's right, the specs are not "impressive". If impressive specs is what you are looking for, this instrument is not for you.

I personally use this instrument because of its usability and because it has 3 channels (which I indeed make use of, depending on the project). I don't care about 10 or 20 mVpp ripple, but I care about usability. And I like the NGE's UI and UX very much. (It's also a good-looking PSU, if that makes sense.) And, of course, it should protect my stuff from the occasional short, which it does very well.

I am using it on analog VCO stuff, and for now everything works fine.

[RBBVNL9]

It is not stated explicitly (as far as I can see), but I would assume that the programming accuracy is specified with no load.

Mmm. That’s an interesting point. I once understood that ripple and noise specs are usually provided for full load (after all, in a classical design, it is under load that capacitors discharge and ripple emerges). Would program accuracy be different in that respect?

So you would have to allow for another 0.1%+20mV due to load regulation.

Not sure where you take that number from. In the specs, I see that number for "Readback accuracy" but I understand that number to reflect the values shown on the voltmeter on the front panel, but that would be something different.

[switchabl]

I may be wrong. But it seems to be the case for Agilent power supplies. In any case, with datasheets I usually assume that all error sources may add up unless otherwise stated. Arguably if it included everything, we could just call it "output accuracy" and not list load/line regulation at all 

Load regulation is listed on p.8 (https://scdn.rohde-schwarz.com/ur/pws/dl_downloads/dl_common_library/dl_brochures_and_datasheets/pdf_1/service_support_30/NGE100B_bro_en_5216_1370_32_v0100_120dpi.pdf)
< 0.1% + 20mV for a load change from 10% to 90%.

[RBBVNL9]

Load regulation is listed on p.8 (https://scdn.rohde-schwarz.com/ur/pws/dl_downloads/dl_common_library/dl_brochures_and_datasheets/pdf_1/service_support_30/NGE100B_bro_en_5216_1370_32_v0100_120dpi.pdf)
< 0.1% + 20mV for a load change from 10% to 90%.

Oh yes, you are right, I see that now. Overlooked it. It also has the "±" sign.

[justanothername]

Programming accuracy: This is (in my understanding) no specfication that describes the dynamic behavior of the unit. It is what you get in voltage when you set a voltage.
I'm thinking about linearity of the DAC, not low frequency noise of the output. So for instance, if you want to set 4V you may get 4.034V because of (shitty) DAC but this should be stable within noise and load regulation specification.
Maybe I'm just completely wrong here.
It's the accuracy vs precision thing:
https://commons.wikimedia.org/wiki/File:Accuracy_and_Precision.svg

[RBBVNL9]

@justanother name: this is an interesting thought.

In this article, the same is explained in the context of a measurement instrument. A recommended read. In analogy with your picture with a target, for a 'perfect' measurement all dots(which are measurements over time) are exactly on the bull's eye.

Yet, my interpretation for a PSU is as follows: the provided value explains that we were to connect the perfect meter above to the output of the PSU, then at any time, the readings of that perfect meter would be within the 'inner circle of your target'. This requires:
- an internal measurement function in the PSU that is sufficiently accurate to reach that goal,
- an internal measurement function in the PSU that is sufficiently precise to reach that goal (one might average a bit over time to facilitate this),
- an internal mechanism that is good enough to make the actual output track the internal measurements within the given specification.

My take...


-     

[kladit]

The NGE100x has a adjustable limit for current and a feature called fuse, which also allows to set a current limit.

The difference between these two features is that when a current greater than then the adjusted limit
is flowing the current limit feature reduces the voltage to a level that allows a contionous flow of
maximal the before adjustet current limit, the fuse feature instead switches off the voltage,
so no further current can flow.

This fuse feature is not well thought to an end.

Most circuitry include one or more electrolytic capactior(s) which to get loaded will cause a higher current flow,
the so called switch on current,

To this or a little greater current the current limit  of the power supply has to be adjusted to allow for normal
switch on behaviour of the device under test.

But there is no way in the NGE100x to adjust the fuse current afterwards, when the normal steady current of the device under test flows.

I want the fuse to protect the circuit most and therefore it is needed to set the fuse current later on to a current value
less than the switch on current.

That is not possible with the NGE100x!

There are two solutions to solve this.

A) The initial value of the fuse is set to the same as the current limit and is allowed to be change later on to another (mostly lesser) value.

B) The different (current limit and fuse) current values for are allowed to set first together with a delay time
(to allow the switch on current to happen) for the fuse to get active.


R&S guys, you know the problem now, I am awaiting for a new firmware.

Regards Klaus

[RBBVNL9]

@ kladit,

A few thoughts:

1. The NGE series has a 'fuse delay' setting. In the manual, this is described as "The fuse delay function is intended to ignore the current peaks set above the current limit that occur during the time set in the fuse delay. This prevents the fuse to be triggered in case of a capacitive load." Seems like what you are looking for!

2. Alternatively, for the situation you described, you might want to use multiple channels in the NGE (there are three identical channels, after all!). You would set a first channel for the longer time protection (current) values you wish, and a second channel - in parallel - that is capable of suppling the higher current during start-up.

3. Moreover, the EasyArb function allows to set different time periods with different current settings.

GL!

[kladit]

@RBBVNL9

The fuse delay  is not relative to current limit. It just makes the electronic fuse behave like a slow wire fuse.

This is not what I meant. The electronic fuse should switch off the voltage as fast as possible and even for a
short increase of current above the set limit in oder to protect the DUT.

Therefore its current limit should be adjustable after the switch on current has happend.

I don't think this is too difficult to implement for R&S and would make the NGE a more valuable power supply.

[RBBVNL9]

But there is no way in the NGE100x to adjust the fuse current afterwards

Are you sure? I just tried this on my NGE, and while the output is on, I can just change the current at which the fuse trips at any moment to the desired value (note that when the Fuse function is activated, the current values you can set (and which are shown in white font on the display) relate to the fuse tripping value, and not any more to the current limiter value). I checked this with an electronic load, and the fuse behaves exactly like you would expect it to. 

You can also automate the process with EasyArb. Just tested this as follows:
- Activated the Fuse function
- Set EasyArb step 1 at 5V, 2A, 5 seconds
- Set EasyArb step 2 at 5V, 1A, 100 seconds
- Connected an electronic load set at 1.5A
- Started the PSU and started EasyArb

And, indeed, after 5 exactly second, the fuse tripped.

[kladit]

@RBBVNL9



Question: How can one switch off the fuse function and change the behavoir to current limit only?
               That means the current stays and the voltage goes down to keep the current the same
               with a sinking value of the load resistor.

[RBBVNL9]

Not sure I understand your question. Earlier, you asked:

The electronic fuse should switch off the voltage as fast as possible and even for a short increase of current above the set limit in oder to protect the DUT. Therefore its current limit should be adjustable after the switch on current has happend.

I think I have shown above how that is done on the NGE.

But now your question is:

How can one switch off the fuse function and change the behavoir to current limit only? That means the current stays and the voltage goes down to keep the current the same                with a sinking value of the load resistor.

What you describe is the default working mode of the NGE. This is the way this PSU it behaves until you active the Fuse function (fuse trip mode) for a given channel.

If your question was meant to be whether you can switch between fuse trip mode and current limit mode while the channel output is activated then my answer would be that, to the best of my knowledge, this is not possible. But I don't see exactly why you would like to do that, and it would not offer the protection of your DUT that you were looking for.

[kladit]

@RBBVNL9

The reason is i did this ..

I switched the power supply on, pressed CH and and adjusted a current.
Then I switched on OUTPUT and increased the load current.
At the point the load current increased over the adjusted current the voltage decreased
ang the numbers got red. Ok , behavior expected.

Then I switched OUTPUT off and pressed FUSE and  CURRENT and adjusted for lower fuse current.
Then I tuned my load to blow the fuse. The word fuse got red and the voltage got switched off. Ok , behavior expected.

Then I set my load back, switched  CH1 on again, FUSE lights got green again,  pressed CURRENT and was able to
decrease the current setting to a value lower than my load current and then the fuse 'blowed' again.

So you are right and I was wrong. The fuse current is adjustable later on to a lower value than
the value adjusted for current limit.

In other words: as long as the word FUSE shines up the current button adjusts the fuse current and not
the current limit current.

But up to now I found no other way to get rid of the FUSE  than to switch the NGE100 off and on again.
Therefore the question in my last post.

It is a little inconvenient to re-adjust the fuse current limit to a higher value every time the fuse
got blown and you switch the output on again and then, after the load current of the capacitors has settled,
re-adjust it to a lower value again.

So my wish to R&S now goes for a adjustable fuse delay time  after channel (re-)activation.

Thanks for forcing me re-thinking the whole problem.

[RBBVNL9]

Happy to hear this addressed your issue.

As to whether you really need to turn of the PSU off altogether in the case you mention, let me check that tomorrow.

[lucasc]

Hi @justanothername,

What did you end up doing? Did you send it back, or was it something that could be fixed?

I'm having the exact same problem and I agree with you that this is not acceptable for a PSU of the level and cost. If this is the expected performance, I'm definitely sending it back. I also noticed that if I move the voltage up and down with the output turned off, the output voltage shows a negative step of about 450mV for about half a second, which is crazy. I've attached the image of the negative step I just mentioned about.

Looking forward to your feedback.

[RBBVNL9]

Hello Lucasc,

I also noticed that if I move the voltage up and down with the output turned off, the output voltage shows a negative step of about 450mV for about half a second, which is crazy.

Never noticed that before, but you are right, I can indeed replicate that. With the output being turned off, it's there every time when you move the voltage setting from 4.10 V down to 4.0 V.

Very very weird. This should definitely be corrected!