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Thread: Noise problem on Agilent oscilloscopes


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Nestor_Groel

Posts: 53
Registered: 09/15/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 9, 2011 11:27 AM   in response to: Coris in response to: Coris
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Good work. This detailed explanation convince me that the inner shielding it´s insufficient and need some improvements. The small "caps" to GND and line may be varistors to absorb high voltage peaks. I´m trying to convince myself to alter my scope to confirm that improving shielding reduce the noise, but after the comment of Porker i´m afraid that in my scope the noise it´s at circuit level. Thanks for the explanation, I still waiting for somebody in Agilent that explain why Agilent not improve the shielding in the design, perhaps exist a serious explanation and justify the actual shielding.
Willco788

Posts: 110
Registered: 05/28/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 9, 2011 4:38 PM   in response to: Coris in response to: Coris
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The EEV Blog has two videos where Dave Jones performs an X3000 and X2000 teardown. You can view the insides including the power supply and input shielding.

http://www.eevblog.com/2011/02/15/eevbl ... -teardown/

http://www.eevblog.com/2011/02/21/eevbl ... -teardown/
Coris

Posts: 86
Registered: 10/29/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 10, 2011 1:48 AM   in response to: Coris in response to: Coris
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Attachment Picture 20.jpg (228.8 KB)
There is another detail about main power supply in Agilent 20xx, which I forgot to notice about here. I`m not sure if this could be a issue for all the PSU in those Agilent devices or it was only in my case. But I suppose this type switching PSU Agilent use in their devices is work this way. The main capacitor in this PSU is running very hot (more than 40 degreeC). This mean a high ripple current and/or a very bad quality electrolytic capacitor. As you can see in the attached picture, after approx 10 working hours, this capacitor exhibit an deformation on its top... This power supply is running all the time as long the device is connected to the main power, even when is off. When the scope is off the fan is not working and no any cooling for that always running PSU... It could be safe like this (as long as the safety tests of the product are done/passed...), but I personally do not like to have that capacitor at more than 40 degree all the time, even when I do not use the scope.
I just found out in the last that Dave Jones in his blogg have noticed too that the Agilent scopes of 2000/3000 series consume 6W of main power when are off... Now I understand that this 6W goes in to that capacitor to get it hot at more than 40 degree when one not use the scope... This is just stupid!
So, the users of those type scopes have to be aware about this detail...
DaveDE

Posts: 11
Registered: 11/12/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 12, 2011 9:39 AM   in response to: Coris in response to: Coris
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Here is an Agilent application note discussing oscilloscope vertical noise characteristics. It's interesting how the note mentions that vertical noise specifications for oscilloscopes are an important parameter but no where in the 2000/3000 data sheets is the noise specified.

cp.literature.agilent.com/litweb/pdf/5989-3020EN.pdf

By the way it's also interesting to note that on 2000 and 3000 series oscilloscopes the vertical gain ranges of 1mV/div and 2mV/div are simply digital zoom functions and do not change the input channel sensitivity (at least that's the way I read the data sheet). So it would seem that the 1mV/div and 2mV/div settings don't have much real value. Too bad.

I'm wondering if someone could please post a screen shot of what the noise floor looks like with vertical gain set to 4mV/div and no scope probe attached. Also, state what model scope is used for the test and make sure bandwidth limiting and any filtering is turned off. Thanks.
Coris

Posts: 86
Registered: 10/29/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 12, 2011 12:51 PM   in response to: Coris in response to: Coris
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"
Here is an Agilent application note discussing oscilloscope vertical noise characteristics. It's interesting how the note mentions that vertical noise specifications for oscilloscopes are an important parameter but no where in the 2000/3000 data sheets is the noise specified.

cp.literature.agilent.com/litweb/pdf/5989-3020EN.pdf

By the way it's also interesting to note that on 2000 and 3000 series oscilloscopes the vertical gain ranges of 1mV/div and 2mV/div are simply digital zoom functions and do not change the input channel sensitivity (at least that's the way I read the data sheet). So it would seem that the 1mV/div and 2mV/div settings don't have much real value. Too bad.

I'm wondering if someone could please post a screen shot of what the noise floor looks like with vertical gain set to 4mV/div and no scope probe attached. Also, state what model scope is used for the test and make sure bandwidth limiting and any filtering is turned off. Thanks.
"


I`ve read earlier that note you mention. My personal opinion after reading this Agilent text is that is a kind of excuse, explanation/story to get the users/customer used with the idea that Agilent have quite high noise level on inputs of their devices, and is nothing wrong with this... Unfortunately, I haven`t read this and haven`t been deeper into this "story" before buying my Agilent DSOX2012...

Else, I can not fully agree with your opinion about a digital zoom used for the 1mV vertical range. As the noise increase on this range, comparing with the 5mV range, have to be about a changing of input sensitivity. Could be usefully that Agilent him self should clarify this (and the rest too...).
Unfortunately I didn`t think to take some screen shots before improving the shielding and the PSU in my scope. But I will come in the near future with same shots about how it looks the noise now in my device.

Overall, the worst situation now (at least for me) is that I can not fully trust the measurements (in low level signals) with this Agilent scope. I have to think twice about what I see on the screen... It is the signal or it is some (internal) noises? This is very bead when is about a measurement device! Don`t you think Agilent?
Before be personally aware about noise problems in low level signal in this my DSOX2012, I just used my bren new trusted scope to measure the parameters of some power supplies. I didn`t knew at that moment that the noise, high frequencies and all kind of spikes I`ve seen on the output of the PSU`s I`ve measured, was indeed coming from inside of my own scope... I concluded that was wrong with that PSU... Was actually not the case, but I was put in a quite delicate (unpleasant) situation...
In old days, when one had a quality scope to work with, one had fully trust in that HP, Tektronix, or what it was made by that device. Nobody couldn`t even think that a HP company, or Tektronix could be on the marked with a non high quality and very trustfully measurement instruments. That because the customers paied the price to have full trust in theirs measurements using a device made by a highly trustfully company. Now those days it seems that this trust is broken down... Like in this Agilent (noise level) case...
DaveDE

Posts: 11
Registered: 11/12/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 12, 2011 3:32 PM   in response to: Coris in response to: Coris
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The Aglilent data sheet for these scopes reads:

" ** 1 mV/div and 2 mV/div is a magnification of 4 mV/div setting. For vertical accuracy calculations, use full scale of 32 mV for
2 mV/div sensitivity setting."


I take this to mean that 1mV/div and 2mV/div settings is digital zoom. This makes sense because they say to use 32mV full scale for vertical accuracy calculations. 32mV is 8 vertical divisions times 4mV/div.

I was just about to purchase one of these scopes. Perhaps I will try to get a demonstration first.
Coris

Posts: 86
Registered: 10/29/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 12, 2011 3:41 PM   in response to: Coris in response to: Coris
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"
The Aglilent data sheet for these scopes reads:

" ** 1 mV/div and 2 mV/div is a magnification of 4 mV/div setting. For vertical accuracy calculations, use full scale of 32 mV for
2 mV/div sensitivity setting."


I take this to mean that 1mV/div and 2mV/div settings is digital zoom. This makes sense because they say to use 32mV full scale for vertical accuracy calculations. 32mV is 8 vertical divisions times 4mV/div.

I was just about to purchase one of these scopes. Now I'm not sure if I should. Perhaps I will try to get a demonstration first.
"


Yes... it looks like you have right... :?
Nestor_Groel

Posts: 53
Registered: 09/15/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 12, 2011 10:35 PM   in response to: Coris in response to: Coris
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I just write to Algoss (forum moderator) to obtain some Agilent answer. I repeat, I still trust in Agilent, one of three of four reputable brands and perhaps the oldest ( for this excellence we buy Agilent isn´t it? ) and believe that some good explanation it´s behind these facts and I like to read that Agilent says. I can not believe that there are reasons for not properly shielding an oscilloscope.
Coris

Posts: 86
Registered: 10/29/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 13, 2011 1:27 AM   in response to: Coris in response to: Coris
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"
I just write to Algoss (forum moderator) to obtain some Agilent answer. I repeat, I still trust in Agilent, one of three of four reputable brands and perhaps the oldest ( for this excellence we buy Agilent isn´t it? ) and believe that some good explanation it´s behind these facts and I like to read that Agilent says. I can not believe that there are reasons for not properly shielding an oscilloscope.
"


I fully agree: yes, we need answers and some explanations!
They should watch this forum I suppose, as a serious company which prioritise its reputation.... I can see in the forum that it come out about problems in another fields of measurement devices too...
ksmith

Posts: 126
Registered: 08/06/09
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 14, 2011 9:29 PM   in response to: Coris in response to: Coris
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Hello all,

I'm an apps engineer with Agilent. I support scopes. I won't comment on anything internal to the scopes.

A few points and 1 thing for everyone to try.

The 2000X and 3000X scopes are 100% designed in Colorado Springs by Agilent. They are made in Malaysia, by Agilent. Each is tested and calibrated on Agilent's factory floor.

The 4 mV/div setting is the most sensitive hardware setting. Anything below that is magnification in software.

averaging and high res acquisition modes can reduce noise, when used properly. They also have 25 MHz bw limit filters behind each channel that will reduce noise.

1 reason these scopes "look noisey" is because of the update rate: more acquisitions per second -> more apparent peak - peak noise, as seen by a a human eye. I know this is hard to swallow. I think I have a nice, simple way to prove this. Further, as compared with analog scopes, modern scopes typically have more bw, though certainly there are analog scopes in the 100s of MHz range. All else being equal (which is not the case), more bw = more noise.

Please try this:
Get a BNC shorting cap (NOT a load), and stick it over one of the channels. Using a BNC short prevent external noise from enteringt eh scope's front end and all that is left is the raw performance of the scope. Set the scope to 1 mV/div (or whatever setting you want). Make sure the attenuation factor is set to 1:1. Turn on a Vrms measurement. how much noise do you see? do you see anything that should not be there?

To get to 4 mV/div, set it to 5 mV, then press the knob in for Vernier/fine control.
Nestor_Groel

Posts: 53
Registered: 09/15/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 14, 2011 11:02 PM   in response to: Coris in response to: Coris
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Dear KSmith:

Thanks for answer, I really appreciate your effort to answer us, BUT, none that you answer respond to our questions.

Why when the oscilloscope´s internal shielding it´s improved the noise is reduced? Agilent not optimize this point
Coris

Posts: 86
Registered: 10/29/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 15, 2011 12:43 AM   in response to: Coris in response to: Coris
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"
Hello all,

I'm an apps engineer with Agilent. I support scopes. I won't comment on anything internal to the scopes.

A few points and 1 thing for everyone to try.

The 2000X and 3000X scopes are 100% designed in Colorado Springs by Agilent. They are made in Malaysia, by Agilent. Each is tested and calibrated on Agilent's factory floor.

The 4 mV/div setting is the most sensitive hardware setting. Anything below that is magnification in software.

averaging and high res acquisition modes can reduce noise, when used properly. They also have 25 MHz bw limit filters behind each channel that will reduce noise.

1 reason these scopes "look noisey" is because of the update rate: more acquisitions per second -> more apparent peak - peak noise, as seen by a a human eye. I know this is hard to swallow. I think I have a nice, simple way to prove this. Further, as compared with analog scopes, modern scopes typically have more bw, though certainly there are analog scopes in the 100s of MHz range. All else being equal (which is not the case), more bw = more noise.

Please try this:
Get a BNC shorting cap (NOT a load), and stick it over one of the channels. Using a BNC short prevent external noise from enteringt eh scope's front end and all that is left is the raw performance of the scope. Set the scope to 1 mV/div (or whatever setting you want). Make sure the attenuation factor is set to 1:1. Turn on a Vrms measurement. how much noise do you see? do you see anything that should not be there?

To get to 4 mV/div, set it to 5 mV, then press the knob in for Vernier/fine control.
"



Thanks for your (delayed) answer.
I see that you do not want comment with us ( the customers who pay for your company product) the inside of the scopes. It is just happen in this case that the problem(s) is INSIDE the scope(s)... The conclusion is that Agilent (you as its representative in this forum) do not want to answer/comment about the main problem here: customers pay a quite high price to Agilent to get an noisy and not so trusty measurement device. This is nice!
Agilent scopes do not "looks noisy". They are noisy! There is not about apparent peaks! There are real peaks there! And about this fact is nothing write in your product specifications...

I want to inform you that I did exactly as you recommended above: Shorted an BNC connector and plug it in one channel of the scope. I had on the 1mV scale 3-4mV noise in a melange with triggerable pulses on quite high frequency range (approx. 20Mhz). I`ve removed/replaced the the original main power supply (switching) with a serial regulator. I`ve shielded the display, extra and better shield over the channels, over many other places on the main board, and shield over the power board. I have now after all those simple but basic modifications, in the same conditions as above: 1,3 mV (pp) raw noise in the lower range of the spectre, 800µV noise on the mid range, and 400-600µV noise in the higher end of the frequency range of the DSOX2018 scope I own. No any frequency pulses at all!

You tell us that Agilent scope are tested and calibrated on Agilent floor. I just want to ask: your testing floor team can not see the noise in the testing process? What that team do with this? Find such explanations about apparent peaks and apparent noise, that human eyes see on the display of yours scopes? So, what we see there as noise it is not, but an illusion? Is this an Agilent explanation?
By the way final testing of the products. Your test floor team couldn`t see that the main power supply Agilent use in their scopes consume for nothing 6W of power when the scope is off? No any remark from those testing people about that the main capacitor in this PSU get hot (40-50degree C) even when the scope is not in use and its fan is not working? Is this safe enough and is all right to use 6W of the main power to get hot this cap just for nothing?
I know that you will not answer to me at those questions, but answer for your self.

Can you see that the problem(s) of your products are INSIDE? Inside Agilent and inside the products...
M. András

Posts: 2
Registered: 11/13/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 15, 2011 2:29 AM   in response to: Coris in response to: Coris
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"
"
Hello all,

I'm an apps engineer with Agilent. I support scopes. I won't comment on anything internal to the scopes.

A few points and 1 thing for everyone to try.

The 2000X and 3000X scopes are 100% designed in Colorado Springs by Agilent. They are made in Malaysia, by Agilent. Each is tested and calibrated on Agilent's factory floor.

The 4 mV/div setting is the most sensitive hardware setting. Anything below that is magnification in software.

averaging and high res acquisition modes can reduce noise, when used properly. They also have 25 MHz bw limit filters behind each channel that will reduce noise.

1 reason these scopes "look noisey" is because of the update rate: more acquisitions per second -> more apparent peak - peak noise, as seen by a a human eye. I know this is hard to swallow. I think I have a nice, simple way to prove this. Further, as compared with analog scopes, modern scopes typically have more bw, though certainly there are analog scopes in the 100s of MHz range. All else being equal (which is not the case), more bw = more noise.

Please try this:
Get a BNC shorting cap (NOT a load), and stick it over one of the channels. Using a BNC short prevent external noise from enteringt eh scope's front end and all that is left is the raw performance of the scope. Set the scope to 1 mV/div (or whatever setting you want). Make sure the attenuation factor is set to 1:1. Turn on a Vrms measurement. how much noise do you see? do you see anything that should not be there?

To get to 4 mV/div, set it to 5 mV, then press the knob in for Vernier/fine control.
"



Thanks for your (delayed) answer.
I see that you do not want comment with us ( the customers who pay for your company product) the inside of the scopes. It is just happen in this case that the problem(s) is INSIDE the scope(s)... The conclusion is that Agilent (you as its representative in this forum) do not want to answer/comment about the main problem here: customers pay a quite high price to Agilent to get an noisy and not so trusty measurement device. This is nice!
Agilent scopes do not "looks noisy". They are noisy! There is not about apparent peaks! There are real peaks there! And about this fact is nothing write in your product specifications...

I want to inform you that I did exactly as you recommended above: Shorted an BNC connector and plug it in one channel of the scope. I had on the 1mV scale 3-4mV noise in a melange with triggerable pulses on quite high frequency range (approx. 20Mhz). I`ve removed/replaced the the original main power supply (switching) with a serial regulator. I`ve shielded the display, extra and better shield over the channels, over many other places on the main board, and shield over the power board. I have now after all those simple but basic modifications, in the same conditions as above: 1,3 mV (pp) raw noise in the lower range of the spectre, 800µV noise on the mid range, and 400-600µV noise in the higher end of the frequency range of the DSOX2018 scope I own. No any frequency pulses at all!

You tell us that Agilent scope are tested and calibrated on Agilent floor. I just want to ask: your testing floor team can not see the noise in the testing process? What that team do with this? Find such explanations about apparent peaks and apparent noise, that human eyes see on the display of yours scopes? So, what we see there as noise it is not, but an illusion? Is this an Agilent explanation?
By the way final testing of the products. Your test floor team couldn`t see that the main power supply Agilent use in their scopes consume for nothing 6W of power when the scope is off? No any remark from those testing people about that the main capacitor in this PSU get hot (40-50degree C) even when the scope is not in use and its fan is not working? Is this safe enough and is all right to use 6W of the main power to get hot this cap just for nothing?
I know that you will not answer to me at those questions, but answer for your self.

Can you see that the problem(s) of your products are INSIDE? Inside Agilent and inside the products...
"


hi, could you give us some pics about those mods you have made?
Nestor_Groel

Posts: 53
Registered: 09/15/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 15, 2011 4:40 AM   in response to: Coris in response to: Coris
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Coris, I understand you and believe me, AGREE with you, but the sentence

"
Agilent scopes do not "looks noisy". They are noisy!
"


It´s a bit general. I use other Agilent scopes and seems like a Stradivarius, just perfect or better. The 2000 series it´s a new series, perhaps needs some improvements but it´s true that a straight answer for somebody in Agilent about shielding would be nice. It´s true that I´m very unhappy with my oscilloscope too, it´s a very basic an entry level but I select Agilent because I confident with it´s product history and now I notice that perhaps it´s a Rigol rebranded that cost much less. I´m glad if somebody of Agilent can explain me (if exists) the differences in black and white (for example, better ADC, fastest ASIC, etc) even by private message. But I still confident with Agilent oscilloscopes because all of other oscilloscopes that I use are really really good and perhaps my model (as that basic and entry level models from Tek that I use) is a sub Agilent product, with school users in mind or audio users. I don´t know, but yes, a straight answer for somebody in Agilent may be give us some peace of mine.
Coris

Posts: 86
Registered: 10/29/11
Re: Noise problem on Agilent oscilloscopes
Posted: Nov 15, 2011 5:05 AM   in response to: Coris in response to: Coris
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Hi M. András

Yes, this couldn`t be so difficult... But, first I`m still working to this right now. In the first time was only an experiment to see what is happen if... Now I want to finish the work in a better way. This is one aspect. Another one is about to work for free for "Agilent developing (improvement) department". They are Agilent specialist who are paid for this job, not me...
I will think about anyway, after I will finish this work around.

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