DS1054Z voltage differences between channel

[aether22]

I bought a DS1054Z, 2 of the probes were faulty (way way out) so I finally got replacements...

The replacements work fine, but the first 2 channels read 3.04v on the calibration signal, the next 3.12v and the last 3.20v (all vmax)

Additionally this time it is not the probes, as switching the probes does not change what each channel reads.

Sooooo is 0.16v difference between channels 1,2 and 4 enough to be complaint worthy?  A warranty issue?

Also, maybe I am being lame and there is some way I can calibrate it myself?

I tried Autocalibration, but no changes in what each channel read.

[Performa01]

3.xx V what? Vpp, Vrms ... ? (I do not have a Rigol DS1000Z, so I cannot know what the calibration signal amplitude is supposed to be)
What vertical gain setting?
Could you provide a screenshot maybe?

[Fungus]

I'd say it's nothing to worry about.

Oscilloscopes aren't multimeters, the ADCs in oscilloscopes have very high bandwidth and very limited resolution (8 bit).

If it helps: Imagine they work by looking at the pixels on screen (it's not quite true, but it's pretty close).

Look at the signal on screen. Do you see the problem? Noise. It only takes a couple of pixels of noise to cause a few percent error.

Things you can try:
a) Go to Acquire->Mode and set "High res". This gives you a 12-bit ADC. Now adjust the vertical scale/position so that the wave is as tall as possible on screen (think 'pixels' - the more pixels it covers, the more accurate it will be).
b) Turn on the low pass filter to eliminate some noise (press the channel's on/off button and choose "BW Limit->ON")
c) Turn off all the lights and computers in the room. A 'scope will pick up everything and each channel will be slightly different.
d) Calibrate the probes very carefully. Turn on the display of "overshoot" using the measurement menu on the left. If there's any overshoot on the calibration signal it needs to be calibrated away.

nb. Each probe has to be calibrated to a particular channel. You aren't supposed to swap the probes around randomly (that's what the colored plastic rings are for - so you know which probe goes on which channel).

[Fungus]

3.xx V what? Vpp, Vrms ... ? (I do not have a Rigol DS1000Z, so I cannot know what the calibration signal amplitude is supposed to be)

The calibration signal is 3Vpp.

[Fungus]

I just had a look at all the channels on mine. I thought of a couple more tweaks as well.

a) Set "High res"mode
b) Turn on the low pass filter
c) Turn off all the lights
d) Push the vertical scale knob. This allows you to fine tune the vertical scale (I set it to 400mV/div for the readings instead of 500mV).
e) Attach the ground clip of the probe to the ground point underneath the calibration signal output. This seems to reduce the noise a tiny bit.

With these settings I got the following Vpp readings on my DS1054Z.
CH1: 3.02
CH2: 2.99
CH3: 3.05
CH4: 3.05

For comparison, in 'normal' mode with a 1Vpp vertical scale I get these readings:
CH1: 3.08
CH2: 3.12
CH3: 3.12
CH4: 3.04

The values weren't stable though, those are just the numbers I seemed to see most. All of them wobbled around and quite often went over 3.2V (sometimes even over 3.3V).

I also noticed that when the numbers wobbled they always went up/down in steps of 4 (ie. values were 3.04, 3.08, 3.12, 3.16, 3.20, etc. with nothing in between). The resolution of the ADC must be 0.04V at that vertical scale - that's more than 1% of the reading!

Conclusion: DSOs aren't multimeters, they simply don't have the noise immunity or number of bits in the ADC.

(or at least the DS1054Z doesn't... I'm sure the old green screen HP27634837684A will)

[Keysight DanielBogdanoff]

Check the data sheet for their scope's accuracy, these values look like they're probably in spec.

[pxl]

I bought a DS1054Z, 2 of the probes were faulty (way way out) so I finally got replacements...

The replacements work fine, but the first 2 channels read 3.04v on the calibration signal, the next 3.12v and the last 3.20v (all vmax)

The specs said +/-3% Gain Accuracy on full scale. Please set the vertical gain to fill the signal the full range (300mV, if your ref voltage is 3V) and connect the inputs to a known/ref. voltage. These values seem a bit off, yet try it without probes.

[Fungus]

Check the data sheet for their scope's accuracy, these values look like they're probably in spec.

I don't think it actually specifies an accuracy for the voltage readings.

The specs said +/-3% Gain Accuracy on full scale. Please set the vertical gain to fill the signal the full range (300mV, if your ref voltage is 3V) and connect the inputs to a known/ref. voltage. These values seem a bit off, yet try it without probes.

I assume "Gain Accuracy" is the accuracy of the amplifier on the analog front end.

If so, it doesn't really tell you very much. Gain is only part of the story. You still have noise, the 8-bit resolution of the ADC, etc. I'm sure the calibration output signal isn't a precision voltage reference either.

It might be useful if a bunch of DS1054Z owners could post their readings here.

[pxl]

You still have noise, the 8-bit resolution of the ADC, etc.

Averaging (as it was mentioned before) may help. Essentially, it should eliminate the quantization noise. You will still have
quantization error, but in full scale it is less then 0.5%, it is a way more less then the values above.

I'm sure the calibration output signal isn't a precision voltage reference either.

In any case the difference between any of two channels, approximately, should not be larger than the difference between the larger/lower values of the specs, in this case 6%. The process above seems to be enough good to measure the differences.

Anyway, any semi pro DMM should have better accuracy than these values by at least 2 orders of magnitude, hence they measured values could act as a voltage reference here. (Well if you have 2 of these DMMs )

It might be useful if a bunch of DS1054Z owners could post their readings here.

Yes, let's see them

[alsetalokin4017]

"What do you expect, it's only 400 dollars."   

[alsetalokin4017]

3.xx V what? Vpp, Vrms ... ? (I do not have a Rigol DS1000Z, so I cannot know what the calibration signal amplitude is supposed to be)
What vertical gain setting?
Could you provide a screenshot maybe?

"All Vmax" was specified in the original post.

The calibration signal is _nominally_ 3V max @ 1kHz. Even if its true value varies a little from that, all four channels should obviously report the same reading from the same signal, don't you think?  I think the OP's CH4 reading of 3.20 Vmax is out-of-spec, not so much because it is different from "3V" but because it is so different from the other channel readings.

[Fungus]

I think the OP's CH4 reading of 3.20 Vmax is out-of-spec, not so much because it is different from "3V" but because it is so different from the other channel readings.

...sssuming his CH4 doesn't need different probe calibration than the others.

(these things should really be done with a sine wave input)

I might need to have a play with my probe calibration and see how it can alter readings on a square wave.

[Fungus]

"What do you expect, it's only 400 dollars."   

Is your point that "expensive stuff can be better"? 

In that case all you're being is a snob.

If we go down that road then we have to include:

"What do you expect, it's only a $50 multimeter"

"What do you expect, it's only a $10k car"

"What do you expect, it's only a $50k house"

"What do you expect, it's only a $xxx whatever"

Nobody should ever buy anything less than the very best, right?

[pxl]

"What do you expect, it's only 400 dollars."   

Is your point that "expensive stuff can be better"? 

In that case all you're being is a snob.

If we go down that road then we have to include:

"What do you expect, it's only a $50 multimeter"

"What do you expect, it's only a $10k car"

"What do you expect, it's only a $50k house"

"What do you expect, it's only a $xxx whatever"

Nobody should ever buy anything less than the very best, right?

The price should come in to the picture just about the specs (specs values and details). Once it is specified, every unit should be inside the limits.

[alsetalokin4017]

"What do you expect, it's only 400 dollars."   

Is your point that "expensive stuff can be better"? 

In that case all you're being is a snob.

If we go down that road then we have to include:

"What do you expect, it's only a $50 multimeter"

"What do you expect, it's only a $10k car"

"What do you expect, it's only a $50k house"

"What do you expect, it's only a $xxx whatever"

Nobody should ever buy anything less than the very best, right?

You really don't get it? My "point" is that the "what do you expect it's only 400 dollars" seems to be the standard "excuse" whenever someone finds something wrong with a Rigol DS1054Z... and I think I recall seeing "Fungus" make that remark or similar remarks several times when I've reported a bug. Or say something like "Well, I don't use the Vmax measurement so I never see this problem, therefore it isn't a problem anyone should worry about."
 
What do _I_ expect? I expect a product to perform according to its advertisements and specifications, regardless of the price the manufacturer chooses to sell it for. If I choose to pay a certain price for a product, I still expect it to perform according to its specifications, to have all its advertised features work properly, etc. Is this unreasonable? Some people seem to think so; I'm not one of them.

[Fungus]

PS: I was using Vpp for my numbers. I expect Vmax readings will be slightly lower because of noise.

[Fungus]

Some people seem to think so; I'm not one of them.

Yes. And you repeatedly tell us so. In every thread.


That computer you're using to type those posts... how can you possibly use it? I bet it has a long list of less-than-perfect features. How can you even be online at all?

[tautech]

Some people seem to think so; I'm not one of them.

Yes. And you repeatedly tell us so. In every thread.


That computer you're using to type those posts... how can you possibly use it? I bet it has a long list of less-than-perfect features. How can you even be online at all?

You're starting to sound like that "hund", anybody that disagrees with your views of a 1054Z must be wrong ! 

[Fungus]

You're starting to sound like that "hund", anybody that disagrees with your views of a 1054Z must be wrong ! 

Somebody has to add balance to their opinions otherwise newbies might end up believing them.

It's a dirty job, but...

[rstofer]

Somebody has to add balance to their opinions otherwise newbies might end up believing them.

It's a dirty job, but...

Interesting that you should say that!

Until I started reading the 1054 megathread from the most recent backwards, I was pretty much sold on the 1054.  Cost isn't an issue and I have a Tek 465 for the real fast stuff but I know exactly NOTHING about digital scopes.  I have never even seen one!  It's fairly obvious Dave is enthusiastic about the 1054 as are most other members of the forum.  But now I'm beginning to wonder...  Am I chasing 'best scope for the money' down a rathole?  It's clear I can't afford the 'best scope regardless of money' but I'm not looking to buy into a bunch of fairly serious limitations simply to save a few hundred bucks.

Back to the EEVBlog videos...

[Fungus]

Until I started reading the 1054 megathread from the most recent backwards, I was pretty much sold on the 1054.  Cost isn't an issue and I have a Tek 465 for the real fast stuff but I know exactly NOTHING about digital scopes.  I have never even seen one!  It's fairly obvious Dave is enthusiastic about the 1054 as are most other members of the forum.  But now I'm beginning to wonder...  Am I chasing 'best scope for the money' down a rathole?  It's clear I can't afford the 'best scope regardless of money' but I'm not looking to buy into a bunch of fairly serious limitations simply to save a few hundred bucks.

To get something that would satisfy the naysayers you'll have to spend a *lot* more. Three or four times more.

Plus... you won't really get any more features and you might only get two channels.

If you're not in a hurry then wait for the next DS1054Z firmware update (which is due any day now if they stick to their usual schedule). See if the naysayers have any legs left to stand on afterwards.

The "Yaigol" thread is very interesting but does the badly-designed PLL actually affect readings on screen? I don't think anybody's shown it. So...