P5104 40kV 20MHz probes

[FPS]

I'm curious about the P5104 HV/HF oscilloscope probes https://www.alibaba.com/product-detail/20MHz-P5104-1000X-40KV-High-Voltage_1313156951.html It looks like the only HV/HF probe that's even moderately affordable.

I've never used anything but standard passive probes that come with cheap oscilloscopes. Is there anything to know about using probes like that above? is it as simple as set to 1000x and plug and play? Will it function on any 1000x scope?

[alan sailer]

Don't know about the Chinese probe. I've been burned several times with Chinese HV stuff.

A used Tek probe might be a better idea. Both I and a friend have Ebay purchases for about 100$
and both work fine.

https://www.ebay.com/itm/225859689599?epid=1901866401&hash=item3496495c7f:g:i6cAAOSwbFhlSW6b&amdata=enc%3AAQAIAAAAwM2YdL3oAJZ%2FiRA3lUWkQC7MaqgjEStwGSkMrZBsSZowTMiCKwD9lv3comvTjgpyocmP4ijVuVQTqeGo%2FthoEUIKIZr2tyYXCbyeSy6hGa%2BXso8X4Y9OAjH050QzAdLjL%2F7PByxFEeuRjhOHK7Pju6kQbdsRroDfxq8WP9zcpLlj9S1FBqxKw9YPUPIQwk1LIYDOf%2Bxa1EG8bnY1pGFuXlKJQP5yeOMwDW6%2BkxgJ2APmYVeQVQ49v9bvjfqHG9zdgg%3D%3D%7Ctkp%3ABk9SR9z8x7uFYw

If you do buy a used probe make sure that the probe still has the dielectric liquid inside the probe. Look for a level of fluid inside teh transparent tip of the probe.

Cheers.

[Mads Barnkob]

What do you need to measure? Maybe a used differential probe can do the job?

[FPS]

I'm really just after something that will read the signal from standard "hobbyist" HV sources, I have a collection of transformers and drivers that would be interesting. I assume the P5104 is a copy of the P6015 in that they look identical and will be +-20kV DC and even lower at the higher end of the frequency range.

[Mads Barnkob]

I found this 100 kV 2 ns risetime DC coupled probe paper in my PDF collection today. Maybe it can be of use?

[FPS]

Thankyou Mads. The problem I see with is how can one possibly know if the reading you receive is accurate without having something to compare it against, you'd need a calibrated HVHF source to see if it checks OK. They look relatively simple and I assume the cost comes from the small market.

Anyway, I purchased the "Pintech HVP 39pro", the "P5104" in title doesn't seem to exist, those listing it do not have it in stock nor does it seem stockable. The Pintech seems to also be sold under the "Cal Test" brand from Mouser/element14 etc but is significantly more expensive. The cheapest I found the Pintech was $758US.

From what I think I'm reading this probe handles a higher duty cycle then the Tektronix, the tek being limited to 10% at 40kV. I'm in Australia, most US sellers of the Tek will not ship here, the cheapest that would was still about $800US minimum second hand.

Its way way cheaper here but not sure how legit it is (I suspect they've listed a different lower voltage models price):
https://www.globalmediapro.com/dp/A03IV5/Pintek-HVP-39pro-High-Voltage-Probe/

It mostly goes for about $1100US (official store):
https://www.aliexpress.com/item/1047975387.html

https://www.globaltestsupply.com/product/caltest-electronics-ct4028-high-voltage-oscilloscope-probe
https://au.mouser.com/ProductDetail/Cal-Test/CT4028?qs=MLItCLRbWsxyvIaxNmTJHg%3D%3D

[FPS]

The first is driven by a 16kHz 40% duty DC square wave and the second 6kV bug zapper transformer is a 50Hz modified sine wave (stepped AC square wave approximating a sine wave). The frequency and voltage checks true based on spark gap but I have no idea what the waveform should look like.

[davekni]

Sounds like you trust the DC accuracy of your probe.  Presuming that is good (or you have some other DC meter probe for measuring HV) here's what I'd suggest and have used before:  Make a simple low-inductance capacitor from foil on either side of a piece of plastic or glass.  Connect probe across capacitor.  Connect a HV DC supply (such as DC-output flyback) through a high voltage resistor or resistor string to capacitor.  With HV on, short capacitor with a short piece of wire.  The spark discharge will make a rapid fall from HV to 0V.  Capture that step response on scope.  Ideally it will be a clean square step from HV to 0V.  (Alternatelly, make a permanent spark gap across capacitor.  Then charge until gap fires on its own.  A gap with smooth rounded electrodes will make best rapid discharge.)

[FPS]

I'll give that a try Dave thankyou.

I did just test the correlation of the 1000x probe against a 10x probe. I wound a low voltage flyback, 16 turns each side then powered with 12v at 16kHz DC square wave. The correlation was very good though the 1000x probe gave a little lower voltage which may be expected being outside its comfort zone.

First column is 10x, second is 1000x.

Second row is 50% duty, a lot of ringing.

Third row is 90% duty, ringing shrinks to nothing as duty is increased on both probes.

Fourth row is zoomed in square wave output at 90% duty, I didn't know you could get a nice square wave output from a simple winding like that.

[davekni]

I'll give that a try Dave thankyou.

One more thought to clarify:  Rounded electrodes are important for the spark whether a fixed gap or manually moving electrodes together.  A sharp pointed wire will have corona discharge before spark, making a rounded start to the falling edge.

I did just test the correlation of the 1000x probe against a 10x probe. I wound a low voltage flyback, 16 turns each side then powered with 12v at 16kHz DC square wave. The correlation was very good though the 1000x probe gave a little lower voltage which may be expected being outside its comfort zone.

That's a great comparison.  Unless your scope is inaccurate at high gain settings, there is no expected discrepancy due to "comfort zone".  Have you carefully checked compensation adjustment on your 10x probe?  At 15kHz mis-compensation will look like gain error.  Does your 1000x probe also have a compensation adjustment to match scope input capacitance?

Second row is 50% duty, a lot of ringing.

Exactly expected waveform for clamped flyback drive.  Ringing is flyback drive FET and winding capacitance combined with transformer parallel inductance.

Third row is 90% duty, ringing shrinks to nothing as duty is increased on both probes.

Also exactly as expected.

Fourth row is zoomed in square wave output at 90% duty, I didn't know you could get a nice square wave output from a simple winding like that.

With almost-no load on secondary and little winding capacitance (compared to normal HV flyback), leakage inductance has little effect.  Primary voltage is cleanly clamped, by FET on-resistance during low part and FET avalanche breakdown voltage (or other ~120V clamp circuit if you have such on your flyback drive) during high part.

10x probe shows more of an overshoot spike after rising edge.  That may be real depending on flyback driver construction.  The lack of overshoot on 1000x probe trace likely indicates some high-frequency roll-off.  Probably in the low MHz range.  Zoomed in capture of each would help estimate roll-off.  (Presumes 10x probe is accurate reference.)  I'd say this is impressive performance still even if there is some response drop before 20MHz.

[FPS]

You are right, compensation was out a bit on the 10x, the 1000x does have adjustment although it will not read from the low voltage signal generator on the scope.

Here's the cap discharge attached, it looks good. There was no resistor so its a bit squashed.

Also a trace from an 8" plasma glob. 1000x connected to HV, and 10x probe sitting about a foot away to match amplitude.

[davekni]

Here's the cap discharge attached, it looks good. There was no resistor so its a bit squashed.

To check step response (frequency response), need to zoom way in to falling edge.  20MHz bandwidth should have a ~17ns fall time from 90% to 10%.  Yes, may be a bit hard to tell without charging series resistor.

[FPS]

Ok, can do. This is the same setup through a 25Mohm resistor.

[davekni]

Ok, can do. This is the same setup through a 25Mohm resistor.

Capture looks fine.  Needs to be expanded to a couple captures at say 10ns/div and 100ns/div to see details at falling edge, at least if you want to know frequency response of your probe.

[FPS]

Oh I see, not sure what I'm looking at but this is zoomed to 50ns. Hit the limit of that little transformer it died straight after photo was taken.

[davekni]

Oh I see, not sure what I'm looking at but this is zoomed to 50ns. Hit the limit of that little transformer it died straight after photo was taken.

Foil capacitor combined with wire length to spark gap is making a resonant circuit at 8MHz.  Prevents measuring probe response to 20MHz.  If you care about that, change the spark gap.  Make the foil extend past the plastic insulation sheet.  Use a steel ball and some piece of rubber or other soft material as back-up to form rounded bump on each piece of foil to form spark gap.  Then the only inductance is the wide foil electrodes combined with the very short thin spark (which will be the dominant part of inductance).  Discharge edge will be much steeper with less ring.  Of course, need to replace transformer too.  If you don't have a resistor in series, that is a likely reason for transformer failure.
Of course, if you are happy knowing that your probe has at least reasonable response to 8MHz, no more testing is needed.

[FPS]

It's not actually foil but thin Al plate in the cap which I'd made previously for something else. I did try clamping a couple electrodes that I'd made for a spark gap apparatus to the effect as shown (I'm not actually sure what I'm meant to be looking for). This time it's a 30kV transformer out of a CO2 laser.

But regardless I'm content, it seems to function well within any role I'd place it in. I don't even know why I've got it haha but I'm sure if I hadn't spent the grand on that I'd have pissed it away on something even more frivolous.

[davekni]

That looks much more like expected, and quite reasonable for 20MHz probe.