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TDS3054, TDS5054 & MSO4104, Pulse Voltage Reading Comparison
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daveyk:
Interesting Comparison.  All three scopes are ISO17025 Calibrated/Certified.  The same custom 100:1 scope probe is being used with all three scopes.  All three scopes were on four >4 hours.

My "Golden Standard" is the TDS3054 with a TDS3AAM Advanced statistics module.

Please see the attachment. 

I am most disappointed in my MSO4104.  Its voltage readings are ~2%-~2.8% lower than either the TDS3054 or the TDS5054.  When I use these scopes, my recorded readings of the pulses should be within 5% of the previous year's readings, and within a +/-10% of "ideal" reading as published by the equipment manufacturer.  The MSO4104 (my favorite new baby) is already starting out with almost 3% differences from the MFG "golden standard" TDS3000 series that their spec is based on.

I had a friend (recently passed) that swore scopes were just funny money reading voltages and pulse widths. No two would read the same.  Heck you get different readings between channels.  He was a huge fan of his 1GHz BW Leckroy.   He swore by it, but still complained that we could not get the same readings on the same instrument.  He said the MFG was wrong to set the standard using a Tek TDS3000 series. Anyway, I wish he were still with us to see this study I did this afternoon.  We could talk for hours on this alone.   

Anyway, I though I would share it with everyone here as an FYI.
2N3055:
That is normal.
Did you read datasheets for these scopes?
Also did you check attenuation of probes?
For really critical work they have to be calibrated and verified before measurements..

There are scopes with tighter vertical accuracy specs (for instance SDS2000X HD has 0.5% vertical accuracy).

But I agree that it is important to discuss and raise awareness of this.
Nice measurements.

daveyk:
Thank you.  What is looks like is a baseline offset on the MSO4104 on the 58.0v range.  I ran the compensation calibration routine (took 20 minutes, made no difference).   On the MSO4104, it matched the TDS5054 if I use P-P rather than MIN).  Hmmmm... the MSO4104 has an SPC error on some vertical ranges.
daveyk:
"Also did you check attenuation of probes?"

Same probe used on all three scopes.  It is a custom 100:1 probe.  The front end (probe end) is basically a 40dB attenuator feeding a 1 meter coax with a 50 ohm terminator on the Scope's end. 

Like the probe or not, it is used by the MFG and it is buildable consistent.   Get 10 Tek Probes, all compensated properly, and all ten will read different pulse voltages and different PW readings.

The MSO4104 has a different way to tell it what type of probe attached. Instead of selecting 100:1, you tell it's attenuation.  I think there is also a different way too.  I need to look at that and see if it effects the baseline offset.
2N3055:
I don't doubt you do nice work. What I wanted to convey is fact that if you take a very nice (expensive)  Tek probes datasheets, they don't even specify amplitude accuracy there.
I wouldn't be surprised that your custom made probe has more accurate attenuation.
As for word "calibration" I used it in classic metrology way: " verification of accuracy by measuring well know quantity".  i.e. checking scope against accurate voltage source and see what it says.
Both those scopes have best accuracy spec of 1.5-2% and as I said for Tek probes I couldn't find that spec but should not be much more than that.
But in general scopes are no better than 3% all things accounted. Unless you use one of those scopes (like one I mentioned) that have stated accuracy better than that. My 2 12bit Siglents are pretty much in range of nice 4.5digit DMM as far as resolution and accuracy (both do much better than spec as it seems).
My 16Bit Picoscope is even better (that one has guaranteed 0.25% DC accuracy and does better than 0.06%. That Picoscope is main reason that I never bought dedicated thermal RMS meter because it does better job than most. And with those two 12bit scopes I get true RMS meter up to 1GHz BW...

But I digress. Your numbers for accuracy are actually decent. Not perfect but well in spec. Better than that, you need to check if those scopes of yours will let you type in a custom attenuation factor of the probe. With that you can fine tune amplitude accuracy by measuring reference source, and if measurement is done soon after setup in thermally stable environment you can do much better. And after measurement you check reference source again. If nothing moved, you can safely presume your measurement is much more accurate than spec.
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