Products > Test Equipment

Comparison of oscilloscope probes PVP2350 vs PVP3150 vs LF312 vs HV150

<< < (4/5) > >>

CosteC:

--- Quote from: 2N3055 on May 24, 2023, 08:14:11 am ---What is purpose of this  exercise?  What do you try to accomplish?

For a risetime measurement you need pulse source that have (very!) flat top and pulse should be at least 10-20x wider than risetime. Same type of termination.

Modern scopes in general will have brickwall AA input filters and will not have perfect pulse response even with source directly connected to BNC on front.
2. In order to have comparable results for discussion a standard procedure has to be followed: in your case 50Ω  source parallel terminated with 50Ω terminator to scope input and probe input. Only one at a time.
3. BW cannot be determined with pulse source (risetime measurements) you need sinewave generator with 50 Ω source impedance and precise levels (or a way to independently measure calibrate level).
4. Using pulse source, a BW can be roughly estimated (roughly) but pulse source has to have certain characteristics (and you need to know your scope AA filter coefficient. It won't be 0.35 for your scope. And it will change with how many channels are on). Pulse source is used to calibrate levels and pulse response. Clean edges and flat top and pulse width at least order of magnitude wider than risetimes.
5. All of that is good and nice if search of knowledge. In practice, if you need to look at 150MHz + you need to start to think in terms that your probing is part of circuit.. A 10x passive 50 Ω probe made from 450 Ω resistor and a piece of coax will do better job and load circuit much less at 200 Mhz than a 10pf 500 MHz 10MΩ passive probe...
6. Which brings us to the point that in that case you should have bought a scope that has 50Ω inputs if these kinds of signals and measurement is what you need. I personally would not buy a 200MHZ+ (less than 1.5 ns risteime) scope without 50Ω inputs...

--- End quote ---
Thank you @2N3055!

My purpose is to understand why PVP2350 seems to have worse response than 'slower' PVP3150 . Maybe it is better, but I do not understand something...
Probe is mandatory for most measurements I do, this is why I need to understand and trust my probes.
Either it is digital signal I cannot load with 50 Ohm probe, or power signal where voltage is too high. While, as you say, it is impossible to not impact measured circuit, I would like to minimise loading and impact.
And yes, I know perfectly well how low impedance 1:10 probe has at 100 MHz. For this reason I got PVP3150 over older RP2200. 10 pF is better than 17 pF

Scope 50 Ohm input itself is not very useful for me... I know and use all trickery of 1:10 50 Ohm probes, if needed. Bare 50 Ohm

Anyway, I need new pulse generator, one with flat, rectangular top, even when loaded with ~10-20 pF. I will test it with some better scope. Hope 2.5 GHz will be enough.

2N3055:

--- Quote from: CosteC on May 24, 2023, 07:41:32 pm ---
--- Quote from: 2N3055 on May 24, 2023, 08:14:11 am ---What is purpose of this  exercise?  What do you try to accomplish?

For a risetime measurement you need pulse source that have (very!) flat top and pulse should be at least 10-20x wider than risetime. Same type of termination.

Modern scopes in general will have brickwall AA input filters and will not have perfect pulse response even with source directly connected to BNC on front.
2. In order to have comparable results for discussion a standard procedure has to be followed: in your case 50Ω  source parallel terminated with 50Ω terminator to scope input and probe input. Only one at a time.
3. BW cannot be determined with pulse source (risetime measurements) you need sinewave generator with 50 Ω source impedance and precise levels (or a way to independently measure calibrate level).
4. Using pulse source, a BW can be roughly estimated (roughly) but pulse source has to have certain characteristics (and you need to know your scope AA filter coefficient. It won't be 0.35 for your scope. And it will change with how many channels are on). Pulse source is used to calibrate levels and pulse response. Clean edges and flat top and pulse width at least order of magnitude wider than risetimes.
5. All of that is good and nice if search of knowledge. In practice, if you need to look at 150MHz + you need to start to think in terms that your probing is part of circuit.. A 10x passive 50 Ω probe made from 450 Ω resistor and a piece of coax will do better job and load circuit much less at 200 Mhz than a 10pf 500 MHz 10MΩ passive probe...
6. Which brings us to the point that in that case you should have bought a scope that has 50Ω inputs if these kinds of signals and measurement is what you need. I personally would not buy a 200MHZ+ (less than 1.5 ns risteime) scope without 50Ω inputs...

--- End quote ---
Thank you @2N3055!

My purpose is to understand why PVP2350 seems to have worse response than 'slower' PVP3150 . Maybe it is better, but I do not understand something...
Probe is mandatory for most measurements I do, this is why I need to understand and trust my probes.
Either it is digital signal I cannot load with 50 Ohm probe, or power signal where voltage is too high. While, as you say, it is impossible to not impact measured circuit, I would like to minimise loading and impact.
And yes, I know perfectly well how low impedance 1:10 probe has at 100 MHz. For this reason I got PVP3150 over older RP2200. 10 pF is better than 17 pF

Scope 50 Ohm input itself is not very useful for me... I know and use all trickery of 1:10 50 Ohm probes, if needed. Bare 50 Ohm

Anyway, I need new pulse generator, one with flat, rectangular top, even when loaded with ~10-20 pF. I will test it with some better scope. Hope 2.5 GHz will be enough.

--- End quote ---

Thank you for the answer. I wasn't trying to be patronizing just to make a summary of all relevant facts at one place.

As an experiment you could try replacing transmission line discharge coax on your avalanche gen with a longer one... Pulse width is defined by pulse propagation time in coax..

A passive 50Ω 10x probe will have DC load of 500 Ω but order of magnitude lower loading at higher frequencies.. Most modern low voltage logic will happily drive it .... As I said, it is not hard, try it. You need 450 Ω resistor and a piece of coax. Terminate at scope side with 50Ω pass through terminator. A noninductive trough hole 0.25W resistor works well enough for experiment... You can even try 950Ω for 20x probe with even lower loading... For looking at logic levels a bit of noise is not that important as pulse fidelity...

David Hess:

--- Quote from: 2N3055 on May 24, 2023, 08:14:11 am ---4. Using pulse source, a BW can be roughly estimated (roughly) but pulse source has to have certain characteristics (and you need to know your scope AA filter coefficient. It won't be 0.35 for your scope. And it will change with how many channels are on). ...
--- End quote ---

Could I get a list of DSOs, or DSO manufacturers who do that so that I can avoid them?  Having the bandwidth and transient response change with the number of channels in operation sounds like fun.

tautech:

--- Quote from: David Hess on May 25, 2023, 03:16:32 am ---
--- Quote from: 2N3055 on May 24, 2023, 08:14:11 am ---4. Using pulse source, a BW can be roughly estimated (roughly) but pulse source has to have certain characteristics (and you need to know your scope AA filter coefficient. It won't be 0.35 for your scope. And it will change with how many channels are on). ...
--- End quote ---

Could I get a list of DSOs, or DSO manufacturers who do that so that I can avoid them?  Having the bandwidth and transient response change with the number of channels in operation sounds like fun.

--- End quote ---
Typically any DSO that shares the 1 ADC, those with dual ADC's are better providing the user has the smarts to use the 2 to best effect and best is with an ADC for each channel.
Shared memory also has an impact with less sample points and hence a greater reliance on accurate interpolation.

Truth is most are affected in some manner however most modern DSO's plainly display sampling rates and memory use for each timebase setting so informing the user so they can use that info to best advantage.

CosteC:

--- Quote from: 2N3055 on May 24, 2023, 09:00:18 pm ---Thank you for the answer. I wasn't trying to be patronizing just to make a summary of all relevant facts at one place.
--- End quote ---
No problems.

--- Quote from: 2N3055 on May 24, 2023, 09:00:18 pm ---As an experiment you could try replacing transmission line discharge coax on your avalanche gen with a longer one... Pulse width is defined by pulse propagation time in coax..
--- End quote ---
There is 10-11 ns of coax inside now. You suggest longer delay will flatten top and improve "rectangularity" of rising edge top?

--- Quote from: 2N3055 on May 24, 2023, 09:00:18 pm ---A passive 50Ω 10x probe will have DC load of 500 Ω but order of magnitude lower loading at higher frequencies.. Most modern low voltage logic will happily drive it .... As I said, it is not hard, try it. You need 450 Ω resistor and a piece of coax. Terminate at scope side with 50Ω pass through terminator. A noninductive trough hole 0.25W resistor works well enough for experiment... You can even try 950Ω for 20x probe with even lower loading... For looking at logic levels a bit of noise is not that important as pulse fidelity...

--- End quote ---
I use them for logic sometimes, particularly in test systems where 50 Ω mux is available but not 1 MΩ mux :)

In this case I want to understand PVP2350 behaviour. Looking for nice rectangular pulse generator :) maybe there is something of-the-shelf.


--- Quote from: David Hess on May 25, 2023, 03:16:32 am ---Could I get a list of DSOs, or DSO manufacturers who do that so that I can avoid them?  Having the bandwidth and transient response change with the number of channels in operation sounds like fun.

--- End quote ---
All? Even LeCroy 7300 has two two-channel ADCs. Either 4x10 GSps either 2x20 GSps (CH1, CH3). This is very common architecture. You just need to know what you are doing. I do not think BW or response changes really - sampling changes so you can loose details. However some details are byproduct of AA filters, when your signal is too close to them.

Here is one of my doubts - maybe PVP2350 is better but "distortion" I see is AA filter, as pulse is fast, contains components around 350 MHz or even higher. Maybe PVP3150 smooth those HF components out.

If you will get ancient Tektronix MSO2024B you will get 4x1 GSps always, yet Rigol MSO 5350 devastates this ancient tektronix with 8/4/2 GSps and 200 times larger memory and ton of other features, which better display is most visible (pun intended). Tek has only lower noise...

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod