EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: Mark on April 09, 2015, 05:13:32 pm
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Soon I will need to look at wave shapes and make some measurements which involve 1.2/50us impulses at 10kV. Can anyone recommend an oscilloscope probe for this task? Is it easy to roll my own? I'm not sure if I have the time or patience to tweak a home-made probe, but if it's a case of following a schematic and having it work first time, then I'm willing to try.
Price limit for a bought probe is about 500UK Pounds.
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Hi what you need is a tek p6015 HV probe. If you are lucky you can get one for reasonable cost second hand. Look at the Tesla coil websites for how to make your own probes but if you want high bandwidth the tek is the only option.
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I would not try to make your own. Why risk yourself and your equipment.
I agree with swingbyte that the Tek P6015A would be the best choice, and possibly the P6013A which is an older model. The P6015A is still being sold by Tektronix.
Manuals and data for the two are here:
http://www.ko4bb.com/manuals/index.php?dir=Tektronix/Tektronix_-_Probes (http://www.ko4bb.com/manuals/index.php?dir=Tektronix/Tektronix_-_Probes)
In particular, look at the charts that derate the maximum voltage based on the frequency and duration of measurement.
There's a couple of both types on ebay right now within your price range.
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10kV is a bit too much to do DIY probe if you have no experience, risk is far too high.
There are two reasonable options - differential HV probe and HV probe with divider. Pintek has a range of both types (http://www.pintek.com.tw/ (http://www.pintek.com.tw/)). Other manufacturers also have similar offerings.
Differential probes are more expensive by default, passive HV probes should be cheaper.
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quite agree, unlike normal mains, KV range can jump off to your nearest skin if not careful. and characterising the homebrew probe is just as difficult unless you have high quality KV signal generator.
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50 MHz 1000:1 15kV passive probe
http://www.siglentamerica.com/prodcut-fjxx.aspx?fjid=407&id=25&tid=1&T=2 (http://www.siglentamerica.com/prodcut-fjxx.aspx?fjid=407&id=25&tid=1&T=2)
US$505 + taxes if any
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A basic HV probe is little more than a voltage divider network and some compensation capacitors. You can build one fairly easily and cheaply with just a little bit of care:
https://www.youtube.com/watch?v=jUvSP3BQpvs (https://www.youtube.com/watch?v=jUvSP3BQpvs)
It might not look pretty but it will get the job done.
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Frequency response is going to be pretty lumpy due to the lump constant resistor/capacitor divider in a metal case. Beyond this, this design does not account for probe cable reflections or impedance mis-matches.
Easier, safer and much more accurate results by simply purchasing a Tektronix P6013, P6015 or P6015A
Bernice
A basic HV probe is little more than a voltage divider network and some compensation capacitors. You can build one fairly easily and cheaply with just a little bit of care:
https://www.youtube.com/watch?v=jUvSP3BQpvs (https://www.youtube.com/watch?v=jUvSP3BQpvs)
It might not look pretty but it will get the job done.
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Beyond this, this design does not account for probe cable reflections or impedance mis-matches.
When was the last time probe cable reflections and mis-matches have ever been an issue? Passive probes use lossy coax to prevent any significant signal reflections from appearing despite the gross mismatch between the unknown source impedance, the probe, the probe's cable and the scope's input.
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OK so I decided I'd take a look on ebay and managed to get a Tek P6015. There is a tube of fluorocarbon shown in the photo, but it will still go to 13kV without it, which is enough for me. It hasn't arrived yet.
Thanks for your advice and opinions everyone, I'll let you know how it goes with the P6015.
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Lossy coax alone does not cure the probe problem as it still has reflections/ringing and requires damping in the probe termination and peaking to compensate for the loss in HF response.
This is the probe termination box of a Tektronix P6105 which is spec'd at 100Mhz. It is a pretty basic Kobbe-Polits scope probe using a lead-lag network. Not the best scope probe as it does produce reflections at the probe tip and has less waveform fidelity compared to Tek and other higher quality probes.
Tek P6105, Term box side:
(https://lh3.googleusercontent.com/oMEyKwweDb5ITIqW4Cjh17ol0aSFM-YP6VHrkx9WnXo=w566-h378-p-no)
Tek P6105, Term box bottom:
(https://lh5.googleusercontent.com/--g6xaz7csuQ/VSx_7T-sQ6I/AAAAAAAAB6A/IjoblaZLn9I/w1640-h1044-no/Tek%2BP6105%2C%2BBot.JPG)
This is Tektronix P6106 probe (200Mhz) termination box, it has two inductors and a LOT more Trimmer and Cap adjustments. Why is this?
(https://lh5.googleusercontent.com/-uuZlK5jIooU/VSx_-5k5ZQI/AAAAAAAAB6I/BZb1G_3n58E/w1468-h1044-no/Tek%2BP6106%2C%2BPeak%2Binds.JPG)
Tektronix P6106, termination box's other side:
(https://lh3.googleusercontent.com/-9vkQeRdrmt8/VSx__gaac1I/AAAAAAAAB6Q/oQHW2O4FoAQ/w1420-h1044-no/Tek%2BP6106%2C%2BTrim%2BR.JPG)
Scope probes of this design work well, have low internal reflections with good pulse and frequency response.
Answer to this can be found starting at page 15 in this Tektronix probe book from 1969.
http://www.davmar.org/TE/TekConcepts/TekProbeCircuits.pdf (http://www.davmar.org/TE/TekConcepts/TekProbeCircuits.pdf)
A bit of probe development history:
http://www.vintagetek.org/oscilliscope-patents/ (http://www.vintagetek.org/oscilliscope-patents/)
Low quality, poorly designed and produced probes are a MAJOR source of measurement error. This coupled with inadequate probe application and insensitivity to how the circuit behaves when probed ADDs to the measurement errors. Passive probes are the most error prone due to their loading at HF, probe reflections and grounding problems. Active probes can make a BIG difference when properly applied, Zo and numerous other probe variations can make the different between low circuit reaction to being probed with good waveform-waveshape fidelity and extreme measurement error. Analog folks can be extremely demanding on probe performance. Every lump, bump, ring and all manner of wave shape aberration can have meaning directly related to circuit behavior.
This is the probe termination box from the P6015 HV probe, it is not a simple network and is LOTs of fun to set up. These are often found with the termination box completely out of whack which results in lumpy, bumpy pulse & frequency response. Getting one of these properly adjusted is a good network learning experience.
(https://lh3.googleusercontent.com/-DZY02-us6pg/VSx_7H29LBI/AAAAAAAAB54/mmbfOglU-1g/w1392-h1044-no/Tek%2BP6015%2C%2Bterm%2Bbox.JPG)
Bernice
Beyond this, this design does not account for probe cable reflections or impedance mis-matches.
When was the last time probe cable reflections and mis-matches have ever been an issue? Passive probes use lossy coax to prevent any significant signal reflections from appearing despite the gross mismatch between the unknown source impedance, the probe, the probe's cable and the scope's input.
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Excellent info Bernice! Thank you, I will bear that in mind if I attempt to adjust anything, I'm certainly glad I decided to buy and not make/bodge now.
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If you bought one of the older P6015 probes that require to be filled with fluorocarbon, you can fill them instead with a high voltage stable silicone gel to have them permanently filled. This is the same as in the P6015A. Just make sure the probe works perfectly, before you fill it with silicone gel.
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Beyond this, this design does not account for probe cable reflections or impedance mis-matches.
When was the last time probe cable reflections and mis-matches have ever been an issue?
when you try to diy it yourself. all this while we took this for granted, with off the shelf probe.
Passive probes use lossy coax to prevent any significant signal reflections from appearing..
i will be very glad if you can give me ebay link where to get lossy 50ohm coax. afaik its none, so reflection problem solving is you need to put a resistor at the very tip of your probe side (with some degree of "success"), not at the active circuit or dso side. otoh, yes building a voltage divider and its compensation is easy, the hard part is specifying it with real world signal measurement, in this case, you need HV generator with acceptable output impedance. if its easy to be get, then its easy to be done.
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If you bought one of the older P6015 probes that require to be filled with fluorocarbon, you can fill them instead with a high voltage stable silicone gel to have them permanently filled. This is the same as in the P6015A. Just make sure the probe works perfectly, before you fill it with silicone gel.
Does anybody have any recommendations for the type (and source of it in the USA) of a silicone gel suitable for filling P6015?
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Can you build the HV divider network directly into the circuit being tested, using appropriately rated components?
You can verify the operation at lower voltage, driving the divider from a good square wave or fast pulse, before hardwiring the top to the device under test. You can also verify safe operation of the divider circuit at HV before connecting it to an expensive oscilloscope.
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Lucky for me I still can get R141B, which will probably work in these probes. Still have 5l in a disposacan under my bench. Getting expensive though, but as a cleaner it works wonders, removes pretty much anything organic.
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i will be very glad if you can give me ebay link where to get lossy 50ohm coax.
The cables off of defective probes are always an option. Another possibility is to design the divider network as an accessory for existing probes. Not ideal for precision measurements on fast edges or high frequencies but still good enough in many cases.
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If you bought one of the older P6015 probes that require to be filled with fluorocarbon, you can fill them instead with a high voltage stable silicone gel to have them permanently filled. This is the same as in the P6015A. Just make sure the probe works perfectly, before you fill it with silicone gel.
Does anybody have any recommendations for the type (and source of it in the USA) of a silicone gel suitable for filling P6015?
Contact Ellsworth for Dow Corning type 3-4680
http://www.ellsworth.com/products/by-market/consumer-products/encapsulants/silicone/dow-corning-3-4680-silicone-gel-transparent-blue-210-ml-kit/ (http://www.ellsworth.com/products/by-market/consumer-products/encapsulants/silicone/dow-corning-3-4680-silicone-gel-transparent-blue-210-ml-kit/)
This material has a dielectric strength of 16 kV/mm
I have several of these P6015A probes and one P6015 that I filled with a similar German made silicone gel material
The P6015 with the silicone gel was tested by me to 35 kV pulse signals and I detected no problems
Just make sure you fill it free of any air bubbles.
Hold the probe in an angle and let the silicone gel run down the housing, essentially filling it slowly from the bottom.
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Thank you, HighVoltage - that's great information. I saw some on-line references to people using mineral oil for filling P6015. Do you think that mineral oil would work as well as silicone gel? Were you able to successfully compensate your P6015 after filling it with silicone gel?
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I saw some on-line references to people using mineral oil for filling P6015. Do you think that mineral oil would work as well as silicone gel?
It shouldn't be ANY mineral oil but a product with a high dielectric strength like Transformer oil.
Datasheets will guide you.
I'd go with HV's suggestion.
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Thank you, HighVoltage - that's great information. I saw some on-line references to people using mineral oil for filling P6015. Do you think that mineral oil would work as well as silicone gel? Were you able to successfully compensate your P6015 after filling it with silicone gel?
As tautech said, you can use a high quality transformer oil.
But it is nasty stuff and you don't want to handle it really.
Yes, I was able to compensate the P6015 correctly with the silicone gel as a insulator.
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Excellent information, thanks for posting that.
I have a P6015 that I picked up the other year and I was wondering where I was going to find some r114. That stuff is very difficult and very expensive to find and it has a tendency to leak out of any container, even if you keep it in a freezer to lower the vapor pressure.
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Thank you, HighVoltage - that's great information. I saw some on-line references to people using mineral oil for filling P6015. Do you think that mineral oil would work as well as silicone gel? Were you able to successfully compensate your P6015 after filling it with silicone gel?
As tautech said, you can use a high quality transformer oil.
But it is nasty stuff and you don't want to handle it really.
Yes, I was able to compensate the P6015 correctly with the silicone gel as a insulator.
That's great to know. Thanks again!
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One way to helping to get the air bubbles out for a filled space with silicone or similar compounds is to place the container, in this case the probe body into a larger sealed container and pump the air out creating a vacuum inside the sealed container with the probe body. The difference in pressure will help promote the air bubbles to move out of the filler compound leaving the probe body with much less air trapped inside the filler.
As for home brew probes -vs- high quality commercial probes, it comes down to waveform measurement accuracy and need. These Tektronix HV probes have been used in particle accelerator targets for high energy physics experiments. Since the probe comes apart and has a BNC connector on the main probe body housing, it can be easy adapted to being used for a host of non-standard applications. Measurement demand placed on probes in these applications are not the same as probes being used for hobbyist experiments and related. Demands placed on the resulting data are also very different between hobbyist and physics researchers or individuals doing serious development and research.
What is not often appreciated today venturing into the world of electronics is just how good and how far some of the test and measurement devices pushed the limits of physics and their understanding of nature. The Tektronix P6015 is just one example of Tektronix probes designed and made in the 1960's that are difficult to equal or better to this day. Other Tektronix probe examples are P6046, P6042 and others. Many of these Tektronix products are still in service to this day decades after they were produced.
Bernice
Just make sure you fill it free of any air bubbles.
Hold the probe in an angle and let the silicone gel run down the housing, essentially filling it slowly from the bottom.
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Yes, a vacuum filling would be perfect, but most people do not have access to a vacuum chamber.
These static mixers on the 1:1 mixing material will work great and usually bubble free.
Just discard the first part of material, that come out of the mixing tube.
I did fill my P6015 without vacuum under atmospheric pressure.
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Yes, a vacuum filling would be perfect, but most people do not have access to a vacuum chamber.
These static mixers on the 1:1 mixing material will work great and usually bubble free.
Just discard the first part of material, that come out of the mixing tube.
I did fill my P6015 without vacuum under atmospheric pressure.
(http://www.xl100store.ca/images/P/393850.jpg)
?
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OK, the Tektronix P6015 probe has arrived! The fluorocarbon bottle was empty, no surprise there. There is a very small amount of liquid in the probe, but I don't need it anyway as it can handle 13kV without it.
I also purchased a Testec TT-HVP 15HF as I will need to connect to a couple of places to compare timings.
To check compensation I used a siglent SDG1020 in pulse mode at 20Vpp, 100Hz.
The yellow trace is the Testec TT-HVP 15HF and the blue trace is the Tek P6015. Timebase is 50us. I haven't touched the P6015 but did twiddle the Testec. Do these waveforms look ok?
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You can probably optimize the P6015 compensation a little more to make get rid of the little dip at the beginning of the high side.
But in general it looks really good already.
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Thanks HV, not bad for £50? (70€, $75)
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Thanks HV, not bad for £50? (70€, $75)
£50 is a really good price for this probe and you can get many good years of usage out of it.
One suggestion, you can change the cable to a more modern and flexible cable.
Also, for a quick test of peak to peak voltage, compare your readings with the two probes on the 230V mains outlet.
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Do not remove the residual freon as that is enough to effectively allow the P6015 to work up to 40KV. It is the freon vapor that increases the dielectric strength, probe does not need to be completely filled with freon.
That bump at the pulse edge is likely due to grounding. Before trying to adjust the P6015, remove the probe body from the housing by un-screwing the probe handle, disconnect the BNC connector & cable, then slide out the probe body. Once this done connect the generator ground as close to the probe tip as possible with a 50 ohm termination to the probe tip.
Think 100+ Mhz required system response or 3.5nS.
The edge and top of the step response should improve, then adjust the P6015 termination box carefully trying one adjustment at a time to note it's effect. If the dip goes away with the improved grounding and generator termination, leave the adjustments alone. The pulse edge and top response of the P6015 should be almost aberration free at the edge with an absolutely flat top at the step.
If a probe had that amount of pulse response aberration (both probes as displayed), I would consider it totally un-acceptable, the try to figure out why and what is happening.
Bernice
OK, the Tektronix P6015 probe has arrived! The fluorocarbon bottle was empty, no surprise there. There is a very small amount of liquid in the probe, but I don't need it anyway as it can handle 13kV without it.
I also purchased a Testec TT-HVP 15HF as I will need to connect to a couple of places to compare timings.
To check compensation I used a siglent SDG1020 in pulse mode at 20Vpp, 100Hz.
The yellow trace is the Testec TT-HVP 15HF and the blue trace is the Tek P6015. Timebase is 50us. I haven't touched the P6015 but did twiddle the Testec. Do these waveforms look ok?
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Thanks HV, not bad for £50? (70€, $75)
Hell yeah. :-+
Had ideas of getting one of these years ago, but could never find one at "my" price. :rant:
Follow Bernice's recommendations. :-+
You should be able to find a SM for it that describes adjustment procedure.
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Tektronix P6015 Pulse response using Tek 7104, 7A26. 7B10, EH Research 139B Pulse Generator.
Tek P6015 removed from it's housing, BNC connector direct to the probe tip, On inch wide Copper tape & rubber band from BNC shell to P6015 Case (GND) with a hp inline 50 termination direct at the EH 139B pulse generator output set at 10Vp-p (gen max) ending up with 10mVp-p at the scope input.
Test set up:
(https://lh6.googleusercontent.com/-PGx5wawucHY/VTH29_GTeeI/AAAAAAAAB7g/du27CRJhMK4/w775-h581-no/P6015%2B%26%2BEH139B.JPG)
P6015 @ 20mS / Div
(https://lh3.googleusercontent.com/-IMYqabXSprA/VTIYoZvIv5I/AAAAAAAAB98/UJfFyMN7OG8/w1316-h1040-no/P6015%4020mS.JPG)
P6015 @ 2mS / div
(https://lh4.googleusercontent.com/-3pV8hkMpDh4/VTIZGY6Ol_I/AAAAAAAAB-c/Az6EmUhhK00/w1300-h1040-no/P6015%402mS-1.JPG)
P6015 @ 200uS / Div
(https://lh6.googleusercontent.com/-vQXsKspXqZE/VTIbLDoW3_I/AAAAAAAACAA/PZ9hsbl7lZ4/w1298-h1040-no/P6015%40200uS-1.JPG)
P6015 @ 20uS / Div
(https://lh6.googleusercontent.com/-PG78Wsw4dH0/VTIXtoOEziI/AAAAAAAAB8s/mVhxSh_1Lkc/w1292-h1040-no/P6015%4020uS-1.JPG)
P6015 @ 2 uS / Div
(https://lh6.googleusercontent.com/-p0z7aYe0WbI/VTIY2KWTbBI/AAAAAAAAB-Q/P3462cPgjpM/w1296-h1040-no/P6015%402uS-1.JPG)
P6015 @ 200nS / Div
(https://lh4.googleusercontent.com/-oE2o4Wyo-cw/VTIXoxdtRsI/AAAAAAAAB8c/AM6v4cBnNHM/w1298-h1040-no/P6015%40200nS-1.JPG)
P6015 @ 50nS / Div
(https://lh4.googleusercontent.com/-KhuMNgvfDm8/VTIYqsDXgJI/AAAAAAAAB-I/gu0Z_0wmjYM/w1290-h1040-no/P6015%4050nS.JPG)
P6015 @ 5nS / Div
(https://lh3.googleusercontent.com/-AkW1kJ2aFL0/VTIYLH14EwI/AAAAAAAAB9g/FK7d6_cdgN4/w1284-h1040-no/P6015%405nS-1.JPG)
Images updated.
Bernice
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I have an original handbook of the P6015 and the P6015P
It contains detailed instructions and schematic with real values.
I also have several parts of the probe and compensation box and could take some detailed pictures.
If anyone is interested, let me know and I will scan and post it here.
Also, I just noticed that I still have a fully functioning P6015, still some liquid dielectric inside and still working.
But no original compensation box available.
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Here are some pictures of the original P6015 and its disassembled compensation box.
I bought this one "as is" and someone tried to modify it with a BNC connector at the box
and had removed the cable.
The high voltage dielectric fluid container is new, unused and still full of Fluorocarbon 114
The probe still contains the liquid as well and you can see the level at the bottom.
You only fill as much in to the probe as needed to get the red ring to float.
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I just scanned the original P6015 Instruction Manual
See attachment
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Thanks for posting all that, could be useful as a reference for those seeking this specific information.
Bernice
I just scanned the original P6015 Instruction Manual
See attachment
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Since we're talking about the P6015(A), a question for those who've used this probe:
Which way do people insert the ground spring? It can go either way with the leaf spring towards the tip, or the other way towards the handle.
The documentation seems to indicate towards the handle, but then the edge of the leaf can get snagged on the probe body when sliding it in the outer body, and you have to hold the spring in the right orientation and make sure it's in the inside lengthwise slot to slide in the probe body.
If inserted towards the tip, the leaf is in the direction of the motion when sliding in the inner probe body, and the whole operation is smoother.
The only difference I see is that in the latter there's some sharp corners on the leaf spring now closer to the high voltage, but it's already under the outer plastic, and it's also not protruding any further from where the aluminum ground start anyway.
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It works both ways and really does not make a difference in direction.
Since the leave spring is not getting closer to the tip than the aluminum housing, it will not shorten the high voltage path.
One thing that is important with the P6015A, the the black rubber ring at the front.
Make sure it stays elastic and soft and grease it from time to time with a little high voltage grease for better insulation.
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The thread is fairly old, but in case someone would seek the more detailed information regarding re-filling original Tektronix P6015 probe with silicone oil, please have a look at AN-108 application note, which can be found here - www.reb3.com/pdf/AN108.pdf (http://www.reb3.com/pdf/AN108.pdf)
The document includes also some remarks about modification of the compensation box and tuning of the modified probe.
In case the link would be deactivated, see also the original file as an attachment.
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Caution must be observed when purchasing R114a particularly in smaller quantities as it is likely to be reclaimed .
Virgin refrigerant is required for safe operation as purity of recycled refrigerant may not be sufficient for HV usage .
Ken
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The thread is fairly old, but in case someone would seek the more detailed information regarding re-filling original Tektronix P6015 probe with silicone oil, please have a look at AN-108 application note, which can be found here - www.reb3.com/pdf/AN108.pdf (http://www.reb3.com/pdf/AN108.pdf)
The document includes also some remarks about modification of the compensation box and tuning of the modified probe.
In case the link would be deactivated, see also the original file as an attachment.
That AN108 application note is a good find.
Indeed, I had filled one of the older P6015 with a transformer oil but I did get better results with high quality silicone gel, filled under vacuum.
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Mine came oriented towards the handle. Since I'm having a hard time assembling it the other way I never actually thought about that, also that's the only way the instructions in the manual make sense? Apart from ease of assembly I doubt it's going to have a significant influence on the creepage.
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I asked Tektronix technical support about the orientation of the ground leaf spring a few years back (Apr 2015). The answer:
Hello Mark,
The ground leaf spring should be oriented towards the handle. I attached the user manual which provides image on page 2-14.
Best Regards
The diagram referred to is below.
I've used it in both orientations also, but the official orientation makes more sense since the ground wire is not being launched immediately towards the HV tip.