Same Spec'ed Rigol Probes but Not The Same?

[Mechatrommer]

While probing 100MHz signal using both Original Rigol's Probes set to x10, both showing different phase and magnitude (x10_probe.jpg). The scope is left warmed up 30 minutes and calibrated and both probes are compensated. But when using direct DIY x1 pcb/bnc connection, both showing okay the same signal phase and magnitude (x1_direct.jpg). If the x10 difference is due to ground loop stray inductance, they have both using ground loops and the inductance should be modeled the same between both probes i think. Is this suggesting both probes have different capacitance? and since there is slight attenuation in channel 2 throughout all frequency in x10 setup, Is this suggesting both probes have different resistance? as well?

I read that to better measure high frequency signal, its better to use x10 probe (higher impedance, lower loading , and compensated internal dso capacitance), but from case above, i'm not sure whats going on. i hope to hear some explanation/assumption. thanx.

[Kiriakos-GR]

Question : What is the max P-P voltage input level for this Rigol ? 


 

[Mechatrommer]

Question : What is the max P-P voltage input level for this Rigol ? 

300Vrms, somewhere ±424V or 848Vpp, theoritically, thats what the front panel said.

[bilko]

From the manual ....

Measurement Category
The DS1000E, DS1000D series Digital Oscilloscope is intended to be used for
measurements in Measurement Category I.

Measurement Category Definitions
Measurement Category I is for measurements performed on circuits not directly
connected to MAINS. Examples are measurements on circuits not derived from
MAINS, and specially protected (internal) MAINS derived circuits. In the latter case,
transient stresses are variable; for that reason, the transient withstand capability of
the equipment is made known to the user.

WARNING
IEC Measurement Category I. The input terminals may be connected to circuit
terminal in IEC Category I installations for voltages up to 300 VAC. To avoid the
danger of electric shock, do not connect the inputs to circuit’s voltages above 300
VAC. Transient overvoltage is also present on circuits that are isolated from mains.
The DS1000E, DS1000D series Digital Oscilloscopes is designed to safely withstand
occasional transient overvoltage up to 1000Vpk. Do not use this equipment to
measure circuits where transient overvoltage could exceed this level.

[Kiriakos-GR]

Ok , I have one last question .  
The 100MHz it is RF , and so logically the oscilloscope will need an more powerful source than the 1V
that you have as test source.

Can you build an small buffer to amplify the signal that you have , to 100Vpp ?
Or amplify it in to a minimum of 5% from the total Max range, and this translates to 42Vpp.
And retest ?    

[Mechatrommer]

it got nothing to do with mains, why its popped up in your mind about the mains concern? and why on hell should i amplify the original DUT from 1Vpp (2Vpp actually) to 42Vpp. i know you work in HV-LF, but we work in LV-HF, and amplifying it is not as simple as putting HP step up transformer in the middle. i've not shown you the mV range yet. just explain to me why there is ~45 degree phase shift? on the very same signal probed with 2 probes/terminal?

[vk6zgo]

Your test seems to rule out the DSO,but just in case,swap the probes over (change the BNC connectors over).
If the lead waveform swaps over,it is a problem with the probes,if it doesn't,it is a DSO problem.

If,as seems likely,it is the probes,one suggestion is to adjust one or both probes for minimum phase difference,consistent with a non-distorted calibration waveform.

VK6ZGO

[Mechatrommer]

Your test seems to rule out the DSO,but just in case,swap the probes over (change the BNC connectors over).

how come i didnt think about this. ok, trying it now...

[Mechatrommer]

yes. the probes are the culprit, i've swapped the probe and the display got reversed in respect to probe position (1) and (2). they are not similar. changing the variable capacitance of probe channel 2, i only manage to make either one, make the magnitude closest as possible, or make the phase as close as possible, (3) is decompensated for closest phase match, but worst magnitude difference, but worst, the rigol calibration output is out of compensation (4). so what should i do? take it apart? mod the probe?
note: rigol is just switched ON cold, so smaller phase difference maybe due to rigol is out of calibration. as it gets warmer, the phase difference is got bigger, visibly.

[bilko]

Are the Rigol probes rated for 100MHz ?

[Mechatrommer]

here's from the manual:

The passive probes have a 6MHz bandwidth with a rating of 150V CAT II when the switch is in the 1X position, and a Full oscilloscope bandwidth with a rating of 300 V CAT II when the switch is in the 10X position.

[Kiriakos-GR]

here's from the manual:

The passive probes have a 6MHz bandwidth with a rating of 150V CAT II when the switch is in the 1X position, and a Full oscilloscope bandwidth with a rating of 300 V CAT II when the switch is in the 10X position.

Logically no one would use an 6MHz probe , to measure 100MHz.
Not to say that the oscilloscope are hacked to operate at 100Mhz.  

And the point is that I do not see any point in all this tests.
And as long this oscilloscope it was intended to operate at 50 MHz,
why it should came with 100MHz probe ?


Oh sorry its not your mistake, probably no one told you,
that if you hack your oscilloscope to operate at 100MHz,
that you are forced to spend more cash about getting an true 100MHz probe !!    

The 6MHz bandwidth at 10X becomes 60MHz !! 

[Mechatrommer]

i'll use my intelligence then, instead of spending more money

[saturation]

Although probes are rated the same, they are not identical; that's why you need to 'tune' each probe by compensating them ...  recall there is a series resistor in there and the variable capacitor.  In addition there are LCR parasitics built into the probe.  There is a slight phase change, but its very small.

If you bypass the series resistor by using x1 and lose the phase change, chances are its the resistor causing the issue. Note, x1 is not bad, its just it its frequency response is less, and will roll off at 6 MHz or so.

A 60 MHz Rigol scope needs a 300-500 MHz probe, because if you measure a square wave, just the 5th harmonics will roll the edges at 300 MHz using a 100 MHz probe.  The Rigol I have shipped with RP2200 passive probes, rated at 200 MHz.   300 MHz passive probes really start to cost a lot, about $40-100 each, so I can live with the 100-200 MHz probes which are $5-10 each.



More on probes.

https://www.eevblog.com/forum/index.php?topic=2289.msg32036#msg32036

While probing 100MHz signal using both Original Rigol's Probes set to x10, both showing different phase and magnitude (x10_probe.jpg). The scope is left warmed up 30 minutes and calibrated and both probes are compensated. But when using direct DIY x1 pcb/bnc connection, both showing okay the same signal phase and magnitude (x1_direct.jpg). If the x10 difference is due to ground loop stray inductance, they have both using ground loops and the inductance should be modeled the same between both probes i think. Is this suggesting both probes have different capacitance? and since there is slight attenuation in channel 2 throughout all frequency in x10 setup, Is this suggesting both probes have different resistance? as well?

I read that to better measure high frequency signal, its better to use x10 probe (higher impedance, lower loading , and compensated internal dso capacitance), but from case above, i'm not sure whats going on. i hope to hear some explanation/assumption. thanx.

[Mechatrommer]

mine are also RP2200 written on em.

[saturation]

Yes, as I recall, 200 MHz ships with 60 MHz scope, I don't know what ships with the real 100 MHz 1102e.

http://www.aidetek.com/New_products_info/Photo/RIGOL/RP2200_Manual.pdf

mine are also RP2200 written on em.

[jahonen]

Many scopes (but sadly I think that Rigol does not belong into that class) have adjustment called probe skew adjustment, to compensate variations of the flight time between different probes. That is important if one measures something like digital timing margins.

But it might be the scope itself (sampling not done exactly at same time on each channel), try swapping probes and see if the time difference is reversed between channels.

Regards,
Janne

[A Hellene]

This is Rigol's probes characteristics table:


According to Rigol's RP2200 specifications, the DS1052E's probes are rated to 150MHz and 300VAC when set x10 and to 7MHz and 150VAC when set x1.

The oscilloscope probes are extremely complicated animals, despite the textbooks that describe them as simple passive devices with resistive and capacitive dividers. For example, no x1 passive probe can go further beyond the 20..50 MHz barrier. Why?
Please, read an excellent article by Doug Ford on the oscilloscope probes, that was published at the Silicon Chip in 2009:
The secret world of Oscilloscope Probes.


I barely use Rigol's probes, since I have better results using much better ones (x100/250MHz). Just watch the table below, to see what a difference can a better probe make. By the way, I use the fragile RP2200's only when the signal is very low in amplitude to be measured by the x100 probes.

Now, this is an eloquent example of probe loading, while reading the crystal oscillator output pin ("TOSC2") of an Atmel ATmega8 μC running at 16MHz:

ATmega8: Vcc = 5.04V, DDS disconnected, CKOPT fuse enabled:
TOSC2: 4.76Vpp, loaded with a x100 probe (100MΩ//6.5pF)
TOSC2: 4.48Vpp, loaded with a x10 probe (10MΩ//17pF)
TOSC2: 3.56Vpp, loaded with two x10 probes

ATmega8: Vcc = 5.04V, DDS disconnected, CKOPT fuse disabled:
TOSC2: 582mVpp, loaded with a x100 probe
TOSC2: 312mVpp, loaded with a x10 probe
TOSC2: 184mVpp, loaded with two x10 probes

The "CKOPT fuse" controls the xtal oscillator output swing amplitude and, in consequence, the oscillator's power consumption and fan-out.
P.S. I did not even bother to make any measurements of TOSC2 with the probes set x1 (1MΩ//100pF)...


By the way, "No probes are made equal"!


-George

[Leo Bodnar]

The probes with a x1 / x10 switch are amongst the worst.  I'd much rather prefer plain x10 then a switched one.  I have never seen passive Agilent, HP or LeCroy probe with a switch.

[saturation]

@hellene, great links. The original treatise on passive probes in the 1960s circa Tek manual describes all. However the article linked in siliconechip does have a new lean to it and worth keeping.

See here as was linked on the previous thread.
http://www.slack.com/TE/TekConcepts/TekProbeCircuits.pdf

The RP2200 probe specs is interesting, the link I posted is nearly identical in content, except the US Rigol link has the bandwidth and rise time derated, for the same probe.

@Bodnar, yes, I'd see the switch introduce finite switch resistance and some residual capacitance that can change as the switch is simply used, ages or wears.  Seems like an unnecessary variable when most of the time you'd like the probe to support the highest bandwidth possible with lowest loading.  I'd think in practice 1x is rarely used vs the 10x setting and one can also accidentally set it to 1x by error.

[A Hellene]

Ah, Joe Weber's classic! Thank you for the link, even though I have the document very well hidden, somewhere in my HD drives!

Doug Ford's article above is not linked to Silicone Chip's magazine; it is kindly provided by Doug Ford himself!


Yes, it is interesting that Rigol keeps and distributes two different versions of the same document, even if both of them state to have been printed in 2007; the difference in bandwidth is not due to some sort of some newer edition reprint. Well, either the products are promoted differently or they are different actually, despite the fact that they share the same product name (RP2200), shape and --probably-- manufacturer. Maybe that is because of a possible difference in their target groups. But, who knows these things better than Rigol itself...

By the way, I just spotted another very important difference in those two documents, in the color of two of the probes' marker rings!
This probably indicates that the two different sets of the RP2200 probes might be supplied with two different oscilloscopes.


-George

[Kiriakos-GR]

A new question just born ...

Does those probes haves any markings, serial numbers on them ? something printed on the cable ?
This sort of info it would help the many so to stop scratching their heads about the probe type that they hold in their hands.

 

[A Hellene]

The set of probes that came with my 1052 included a printout of the 150MHz version of the data-sheets, above.

[Mechatrommer]

But it might be the scope itself (sampling not done exactly at same time on each channel), try swapping probes and see if the time difference is reversed between channels.

did that in Reply #8. yes time difference is reversed, so its the probes (capacitance), but attenuation is not reversed suggesting there is difference between dso internal input impedance. picture replayed here.


edit: thanx saturation and a hellene for the link and description. i never saw the RP2200 before due to my ignorance.

[Kiriakos-GR]

Hey what are your doing in here ?
Your local time is 4:33am , go to get some rest.   

[Mechatrommer]

my probe is RP2200 with serial number on it allright. cant take a picture right now, camera's lens offline!. i'm in Batman Project, my sleep schedule has been shifted to 8am - 3pm
just now i tried to profile my FG using direct FG-BNC-PCB-BNC-DSO up to 100MHz sine signal, so it means x1 probing. is that means my reading cannot be trusted?

[A Hellene]

The rule of 1/(2πFC) indicates an additional loading of 15.9Ω!
Fortunately, probe loading is not purely capacitive; but, yes, I would not trust the reading --if any could successfully be done at those frequencies using x1 probes.

Just see the impact the x10 probes had on the 16MHz crystal oscillator of the mega8, in my previous message.


-George

[Mechatrommer]

ok george! i saw your osc measurement earlier, its sensible since x1 with more loading will attenuate the signal further. but i just retried to compare x1 and x10 reading from FG signal, shocking to me, the result are reversed!

100MHz sine signal 50ohm source impedance unterminated:
x1 direct pcb bnc = 4.36Vpp
x10 rigol probe = 3.04Vpp

100MHz sine signal 50ohm source impedance terminated:
x1 direct pcb bnc = 2.48Vpp
x10 rigol probe = 1.52Vpp

what the hell is going on?!

[A Hellene]

Ah, the magic is done by the direct connection using some serious transmission line with low attenuation --if terminated correctly!
By "x1 probing" I assumed that you would use the (extremely lossy) oscilloscope probes, set x1. 


-George

[Mechatrommer]

ok i know whats going on.... ground loop inductance.... again! ok, using spring gnd, i managed to increase the signal in x10, but still not as good as x1. maybe at this frequency, coax shielding is much more important. my intuition telling me.

100MHz sine signal 50ohm source impedance terminated:
x1 direct pcb bnc = 2.48Vpp
x10 rigol probe (spring gnd) = 2.32Vpp

maybe george, you were measuring a high impedance source, that MegOhm input impedance will affect too much on voltage divider. mine is 50ohm source only, so doesnt matter 1M or 10M ohm the attenuation will not be affected too much i think.

[Mechatrommer]

ok thanx george for clarifying

[A Hellene]

I am sorry for the delayed response; I had to refill my empty glass with poison on the rocks!


When the transmission line is not terminated, the source cannot provide any power to the load, since there is not any real load at the end of the transmission line! The measuring device, which is a parasitic load, should ideally be no load at all to the system! Thus, the extremely high input impedance of the test equipment.

Voltage is the reason of current flow; and without any current flowing the voltage reading alone is mostly meaningless --except for debugging purposes, only.

The concept of a matched source, transmission line and load impedance is to transmit as much power as possible to the load. Reading just a ghost voltage at the end of an open transmission line does not really mean anything useful!

Transferring power (or energy) is the challenge, which can only be achieved when there is as much current flow to the load as possible. And the best it can be done, in the real world, is to transfer to the load a little less than half of the power the source can deliver. Either in DC or in AC.


-George


[EDIT]: Additional information.

[Kiriakos-GR]

I love batman projects, and If you had invite me too, I would had bring my own toys too. 

[Mechatrommer]

Reading just a ghost voltage at the end of an open transmission line does not really mean anything useful!

so reading open ended (no load) battery giving a useless result? i believe what you meant by "ghost voltage" is for open ended high frequency signal where transmission line length > wavelength / 4 or according to Jim Williams > 1 inch where things like reflection and standing wave is much more prominent (power not transferred).

[vk6zgo]

Reading just a ghost voltage at the end of an open transmission line does not really mean anything useful!

so reading open ended (no load) battery giving a useless result? i believe what you meant by "ghost voltage" is for open ended high frequency signal where transmission line length > wavelength / 4 or according to Jim Williams > 1 inch where things like reflection and standing wave is much more prominent (power not transferred).

No,it is not the high tech end of things,it is more related to simple voltage divider action.

(1) With paper & a pencil,draw an ideal generator with zero internal resistance.
(This is impossible,but we can imagine it). 
For convenience,make it a 10volt  p-p source.

(2)Add a 50 ohm resistor in series with one terminal of the generator.(A real generator  with 50 ohm output impedance may be regarded as an ideal generator in series with a 50 ohm resistor).

(3) Try various resistor values in series  with the 50ohms,forming a voltage divider across the generator,
& calculate the  voltage across,& power dissipation in the extra resistor.

You will find that the power dissipation across the extra resistor is maximum when that resistor is equal to
the series resistor (50 ohm),& the voltage across it is 5 volts p-p (1/2 the open circuit voltage of the generator).

(4)The voltage across a 1Mohm resistor in the same position will read very close to the open circuit voltage.

This is extremely easy to explain face to face,& very hard to explain via a forum.

VK6ZGO 

[Mechatrommer]

i understand, no need face to face but we try to read voltage, not power, as george termed it as "ghost voltage".
if i measure terminated signal, the unterminated signal will read about twice as that, no "ghost" will flying around, or maybe some misunderstanding here

[A Hellene]

Alright, dear Mechatrommer, it was my mistake. After all, you know that I do not believe in ghosts!

The terms "voltage" as well as "ghost voltage" were not accurate but oversimplified ones. Would it be better if I used the terms "electric potential difference" and "unspecified/phenomenal voltage" instead, respectively? I was trying to start from square #1 since the measuring equipment impedance was very close to the impedance of the circuit under test, something that VK6ZGO explained very well.

The RP2200 probes are not a linear load, since they are loading the test circuit with a combination of a 10MΩ resistance in parallel to a 17±5pF capacitance. In DC their loading is straightforward: 10MΩ! But in AC, things change dramatically as the frequency rises.

For example, RP2200's load at 100MHz is equivalent to a 10MΩ ±2% resistor in parallel to a 72.3Ω .. 132.6Ω one (i.e. 17±5pF parallel input capacitance @100MHz), which equals to a load of an equivalent resistance of 72.3Ω .. 132.6Ω. Of course, this is not a load that can be ignored, since it inserts some significant measurement error to a signal source of 50Ω or 51Ω impedance.

Under these conditions, a reading of 2.32Vpp at the open end of a non terminated 50Ω transmission line using the RP2200 probes would suggest an actual presence of 3.20Vpp .. 3.92Vpp at the test points: A deviation of +38% .. +69% = +53.5%±15.5 of the actual reading --having, of course, not taken into account any possible parasitic elements (as the probe's ground current loop inductance), or standing waves or reflections due to impedance mismatch of the load, and/or the length ratio of the transmission line. Well, this is not just a deviation; this is a faulty reading.

In a similar manner, the DS1000 oscilloscope input impedance at the BNC is 1MΩ±2% with a capacitance of 18pF±3pF. Again, in DC the input capacitance is insignificant; but not in HF (my mega8 16MHz oscillator example) or, even worse, in VHF...


-George


[EDIT]: Calculation errors corrected.

[vk6zgo]

Interestingly,Mechatrommer's results, even if they show errors in absolute value,still follow closely the expected ratio between terminated & unterminated voltages.

There is a bit of error for the direct connection,but the ratio is spot on when using the X10 probe.


100MHz sine signal 50ohm source impedance unterminated:
x1 direct pcb bnc = 4.36Vpp
x10 rigol probe = 3.04Vpp

100MHz sine signal 50ohm source impedance terminated:
x1 direct pcb bnc = 2.48Vpp
x10 rigol probe = 1.52Vpp

By the way, Mechatrommer,picture (1) of reply#8 shows a lot better results for phase error.
Had you already started tweaking the probes at that stage,or was there a measurement error with the results in
your original posting?
You probably are asking a lot of your probes if they are not specified for the same phase error at 100MHz.
A lot of things quote amplitude/frequency response,but phase/frequency response is rarely quoted.



VK6ZGO

[Mechatrommer]

Interestingly,Mechatrommer's results, even if they show errors in absolute value,still follow closely the expected ratio between terminated & unterminated voltages.

i dont see any interesting point there, just headache and losing more hair.

By the way, Mechatrommer,picture (1) of reply#8 shows a lot better results for phase error.
Had you already started tweaking the probes at that stage,or was there a measurement error with the results in
your original posting?

it seems to be, but the fact that the reply #8 phase improvement at (1) and (2) is due to cold rigol startup and test. the 1st posting is the one is done after proper warm up and calibration. thats a luck, not improvement. i only tweaked the probe capacitance on (3) in picture reply #8

You probably are asking a lot of your probes if they are not specified for the same phase error at 100MHz.
A lot of things quote amplitude/frequency response,but phase/frequency response is rarely quoted.

i asked if they are different. simple yes or no. and then you asked me to switch probe which i did. then i got the answer, the answer is yes, they are different. simple as that. as all other matters revolving around us, its "money" matter. if you have complain, you shut up, take out $$$ out of your pocket and buy a brand name one.

[vk6zgo]

The "interesting" thing is that the voltage ratio is what it should be from simple voltage divider theory!
No confusion,all the other effects are important,but the "correctly terminated " source will present a voltage 1/2 that of the same source "unterminated".
Try the same test at a lower frequency,say around 1kHz,to get a good understanding on how it works.


 The Rigol is performing "above & beyond the call of duty" to be able to measure phase
difference at 100MHz,even with your direct connection,so it was definitely a good buy!

I just realised that,when you are measuring phase,you are only doing that,so you can adjust one or both probes for minimum phase error,as shown in your reply#8,ignoring the effect on the normal "Calibrator" waveform.

Switch one or both of the vertical channels to "Uncalibrated",& adjust the variable vertical amplitude control till both signals have the same amplitude on the screen.

You should now have equal amplitudes,& very close to zero phase error on your display.

You can now use this set up to measure phase difference between two separate test points.(As they are unlikely to be the same level,you will probably have to match the vertical amplitudes as before).

When you are finished,simply return the vertical channels to "Cal",& readjust the probes using the "Calibrator" waveform.

VK6ZGO