Author Topic: Scope probes as supplied by Rigol for the low end scopes, a discussion.  (Read 25443 times)

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Offline Lightages

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I kind of hijacked the Review Summary video #703 with a discussion of the quality of probes supplied with the DS1054Z.

The original post I made with an image of an example of how the waveform appeared differently with the RP2200 probes that came with my DS1054Z as compared to the RP3300 probes that came with my DS1052E.
http://www.eevblog.com/forum/blog/eevblog-703-rigol-ds1054z-oscilloscope-review-summary/msg589804/#msg589804
Both scopes were modified to 100MHz bandwidth. The image is linked below.

It was suggested that I needed to change the termination load, measure without the ground leads, maybe the ground lead length difference caused the appearance change, or maybe my signal was not good enough.....

Well I have measured with two scopes, all the available channels, with the cable from the function generator open ended alligator clips, 50 ohm load at the generator, at the end of a BNC terminated cable, with the spring clip ground point on the probes, directly into the function generator, and all the different arrangements that are possible. Yes the observed wave form changed, but there is always the same relative difference of the appearance of the wave form between the RP2200 and the RP3300.

I am either doing something wrong, or there is a visible degradation of the input bandwidth of the scope with the RP2200 model probes.

So two questions:

#1. Are my attempts futile and the apparent change in the displayed waveform is my lack of knowledge. This is a high probability.

#2. Does the performance of the RP2200 actually degrade the total system performance of the DS1054Z ?

Bonus question: If #2 is an affirmative, is this actually a smart move by Rigol to limit the system bandwidth of the scope so that the under sampling with 3 or 4 channels enabled is less of a problem?

Discussion?
« Last Edit: January 21, 2015, 06:27:45 PM by Lightages »
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Online IanB

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #1 on: January 21, 2015, 02:37:52 PM »
Wow. Are we saying the RP3300 probes (DS1052) are better than the PR2200 probes (DS1054)?

If so, that is a little surprising.

On the other hand, Rigol's specifications say that RP2200 are good up to 150 MHz, while RP3300 are good up to 350 MHz. So the RP3300 should be better. If I happen to have a pair of the RP3300 I guess I'm keeping them...
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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #2 on: January 21, 2015, 02:50:49 PM »
My video on this is rendering now.
Here are some screen shots of the two probes, as measured across a 50ohm load on a 100MHz DS1054Z with proper coaxial probe top connector.
 

Offline Lightages

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #3 on: January 21, 2015, 03:14:44 PM »
Wow. Are we saying the RP3300 probes (DS1052) are better than the PR2200 probes (DS1054)?

If so, that is a little surprising.

On the other hand, Rigol's specifications say that RP2200 are good up to 150 MHz, while RP3300 are good up to 350 MHz. So the RP3300 should be better. If I happen to have a pair of the RP3300 I guess I'm keeping them...

I can only guess that Rigol ran out of RP2200 probes when the demand for the DS1052E went up and they had no choice but to ship them with the RP3300 probes to keep shipments moving. They are better probes by spec at least so yes, keep them!
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Offline Lightages

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #4 on: January 21, 2015, 03:17:43 PM »
OK Dave, I will wait and see you video. But it is very surprising to me that I have a real difference in the waveform, and with proper termination. The termination should not matter as long as the impedance of the probes are not significantly low enough to effect the waveform. I did one of my comparisons across a properly terminated, and not terminated cable, and the wave form always changed between the different probes.
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Online IanB

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #5 on: January 21, 2015, 03:22:58 PM »
I can only guess that Rigol ran out of RP2200 probes when the demand for the DS1052E went up and they had no choice but to ship them with the RP3300 probes to keep shipments moving. They are better probes by spec at least so yes, keep them!

Apparently I don't have the RP3300 probes after all, so I guess I can stop dreaming...  :(
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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #6 on: January 21, 2015, 03:23:50 PM »
The termination should not matter as long as the impedance of the probes are not significantly low enough to effect the waveform.

Of course it will be. The 16pF input capacitance is about 100ohms @ 100MHz.
 

Offline Lightages

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #7 on: January 21, 2015, 03:41:02 PM »
Hmmm, I know I am treading on deep water here with my lack of experience with some of these things. The RP2200 specs are 15pF and I measure 14.7pF with my DER EE DE-5000 at 100kHz. At the moment I cannot find my data sheet for the RP3300 probes but I measure 17.5pF at 100kHz??!! Shouldn't the higher capacitance provide a higher load and therefore the appearance of the waveform would look like lower bandwidth?

EDIT


Actually I just measured with both probes' compensation adjusted on the same scope and input and their capacitance is pretty much equal shows the RP2200 with lower capacitance than the RP3300 at 100kHz.
« Last Edit: January 21, 2015, 04:13:19 PM by Lightages »
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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #8 on: January 21, 2015, 03:44:30 PM »
RP3300 spec is 16pF +/- 5pF
RP2200 spec is 17pF +/- 5pF
 

Offline Lightages

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #9 on: January 21, 2015, 03:55:10 PM »
Sorry I edited my post after you posted. The exact measurement I get is 17.6pF for the RP3300, and 14.9pF for the RP2200. I know 100kHz is a far cry from 100MHz, but are their caps really that dependent on frequency between the two models? This after compensating each probe and immediately measuring the capacitance right after.

Edit:

Not equal sorry
« Last Edit: January 21, 2015, 04:04:52 PM by Lightages »
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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #10 on: January 21, 2015, 04:19:23 PM »
Sorry I edited my post after you posted. The exact measurement I get is 17.6pF for the RP3300, and 14.9pF for the RP2200. I know 100kHz is a far cry from 100MHz, but are their caps really that dependent on frequency between the two models? This after compensating each probe and immediately measuring the capacitance right after.

There aren't caps in there, it's the capacitance of the construction of the tip up until the input resistor. It can be quite variable as the spec indicates and yes, will change with frequency.
 

Offline Lightages

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #11 on: January 21, 2015, 04:28:42 PM »
There aren't caps in there, it's the capacitance of the construction of the tip up until the input resistor. It can be quite variable as the spec indicates and yes, will change with frequency.

OK I can understand that caps capacitance ratings can change their value with frequency, but the variable cap for adjusting the compensation is not a cap? :-//

So now that you have asserted that the RP2200 probes have a higher capacitance than the RP3300 probes at 100MHz, I will await your video to see the actual bandwidth measurement for the total system  with the DS1054Z to see if the full 100MHz bandwidth is actually available with the supplied probes.  ;)
« Last Edit: January 21, 2015, 04:30:37 PM by Lightages »
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Offline Lightages

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #12 on: January 21, 2015, 04:41:16 PM »
I think I need to say that my previous experience in electronics was basically limited to 10MHz or so and I have little experience above 25MHz or so. Please excuse my ignorance on this higher realm but I think it is an opportunity to learn about this "higher" frequency for everyone.
« Last Edit: January 21, 2015, 04:43:02 PM by Lightages »
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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #13 on: January 21, 2015, 05:09:33 PM »
OK I can understand that caps capacitance ratings can change their value with frequency, but the variable cap for adjusting the compensation is not a cap? :-//

That is across the 9M input divider resistor.
https://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf

Quote
So now that you have asserted that the RP2200 probes have a higher capacitance than the RP3300 probes at 100MHz, I will await your video to see the actual bandwidth measurement for the total system  with the DS1054Z to see if the full 100MHz bandwidth is actually available with the supplied probes.  ;)

I didn't do that in this video, just tried to verify if there was a pulse response difference difference between two probes on the 100MHz scope. There isn't really any difference.
 

Offline phenol

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #14 on: January 21, 2015, 05:15:34 PM »
how about the pulse response of the scope itself, i.e. terminate the scope intput with 50ohms and connect the sig gen directly?
 

Offline Lightages

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #15 on: January 21, 2015, 05:18:03 PM »
Ahhhh, too bad that you didn't measure the actual response.  :(

Yes I know where the cap is situated in the probe circuit. It doesn't mean there isn't a cap!  >:D

Oh well, I will await an answer for the system response with the RP2200 and maybe vs the RP3300. Maybe someone with better experience than I have and the appropriate equipment can show this.
« Last Edit: January 21, 2015, 05:19:39 PM by Lightages »
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Offline Lightages

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #16 on: January 21, 2015, 05:42:36 PM »
So the RP3300 are rated at a nominal 16pF and the RP2200 at 17pF.  This implies that from the assertion that 16pF is 100ohms that 17pF would be maybe 94ohms. Does this account for the difference I see in the waveform I am measuring? It looks like it might be so from the visual difference I see. I really wish I had something to do this quantitative measurement.  >:(
« Last Edit: January 21, 2015, 07:00:42 PM by Lightages »
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Offline phenol

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #17 on: January 21, 2015, 06:12:26 PM »
i made a few screenshots with a tek dpo3000 scope. The BW is only 300MHz, but the difference in rise time is still measurable.
I probed the terminated output of a 50-ohm square wave source (a VFO for a shortwave RX passive mixer) with the stock 500MHz 8pF probe, the vfo connected directly to the scope using the internal 50ohm termination and finally, using an HP 150MHz 15pf probe.
The input capacitance of the scope is 11.5pF.
The fastest rise time is obtained when the source is coupled directly to the scope. 500MHz probe follows, and the slowest is the 150MHz probe.
The rise time of the source itself is well under 700ps.
obviously, the combined BW of the probe+scope is lower than the BW of the scope alone, eventhough the 8pf tip capacitance should in theory load the source output less than the 11.5pf on the input of the scope.
 

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #18 on: January 21, 2015, 06:16:52 PM »
Oh well, I will await an answer for the system response with the RP2200 and maybe vs the RP3300. Maybe someone with better experience than I have and the appropriate equipment can show this.

It doesn't matter what the actual measured response is, the point is that there was essentially little to no measurable difference between the RP2200 and RP3300 when used on the DS1054Z, and I thought that was what was under question here?
And there is no reason to believe that the RP2200 does not meet its claimed 150MHz bandwidth (3dB down), I would be stunned if it didn't.
 

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #19 on: January 21, 2015, 06:19:05 PM »
So the RP3300 are rated at a nominal 16pF and the RP200 at 17pF.  This implies that from the assertion that 16pF is 100ohms that 17pF would be maybe 94ohms. Does this account for the difference I see in the waveform I am measuring?

No, unlikley that it would, as evidenced by my measurement. Unless you have two probes that are vastly out on on the two edges of the spec or something.
I suspect there is something amiss with your test method.
 

Offline alex.forencich

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #20 on: January 21, 2015, 06:20:13 PM »
Looks like at least one of the probes might not be compensated correctly.  Did you make sure to adjust both probe compensation screws to get the proper flat top with no overshoot or undershoot?
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Offline Lightages

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #21 on: January 21, 2015, 06:21:48 PM »
One of the questions was:

#2. Does the performance of the RP2200 actually degrade the total system performance of the DS1054Z ?
This was in response to the video review where you stated that the probes would not limit the performance of the scope. When I saw a difference I wondered based on what I had seen with my probes compared to the RP3300s

And yes to the last poster, both of the probes were adjusted as perfectly as I could make them. This was done each time I connected and immediately before I made any test.
« Last Edit: January 21, 2015, 06:24:18 PM by Lightages »
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Offline 3roomlab

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #22 on: January 21, 2015, 07:28:05 PM »
what if you measure the capacitance of the 2 probes at 1Mhz and 10Mhz ? is there such an option to measure?

if you compensate a probe @ 1kHz, should you compensate for it @ higher frequencies too? or rather, would the compensation be required in a different manner at higher frequencies? so should there be 2 compensation values for 1 lower (below 10khz) and 1 higher (above 1 Mhz)?
« Last Edit: January 21, 2015, 07:31:16 PM by 3roomlab »
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Offline tautech

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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #23 on: January 21, 2015, 07:36:42 PM »
One of the questions was:

#2. Does the performance of the RP2200 actually degrade the total system performance of the DS1054Z ?
What self-respecting manufacturer would supply a probe that might?
They would be quickly found out and shamed or should be.
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Re: Scope probes as supplied by Rigol for the low end scopes, a discussion.
« Reply #24 on: January 21, 2015, 08:30:33 PM »
One of the questions was:
#2. Does the performance of the RP2200 actually degrade the total system performance of the DS1054Z ?
This was in response to the video review where you stated that the probes would not limit the performance of the scope. When I saw a difference I wondered based on what I had seen with my probes compared to the RP3300s

I mentioned this in my video, but did not actually measure it, and there is a reason for that. The answer is yes, in theory it can, because when you cascade two systems with a given bandwidth, the total bandwidth is always lower, to the tune of the inverse root sum of the inverse squares. Even 1GHz probes would lower the bandwidth a bit. But it's not that simple in passive probing systems like this, but I gave that example anyway.
But the reason I did not measure it is because it has been standard practice for eons for manufacturers to supply the same rates bandwidth probes as the scope, or a bit higher. And Rigol does this, so it's a not a problem. So it was sufficient to just to see if there was any difference between the two, and there isn't, hence the 150MHz probes are just fine. Unless of course you think the 350MHz probes aren't up to snuff either.
 


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