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P6015 what if filled with SF6..????
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right_electronics
Hi fellows!!.
I just bought from epay among other nice instruments,this P6015 ,which seems to come from Westinghouse labs,the probe is old in years ,but I think never used. The fact is that every knows that the original filling gas is no more obtainable. Since I have access to a giant VanderGraf linear accelerator 20MeV,which is filled with SF6 gas"Sulfur hexafluoride" to attain dielectric barrier, and the SF6 gas has at 1 ATM 6 to 10MV/mts of breakdown, mean 2 to 3 times the air strength. This gas is not flammable or poison. Then I wonder ,why not use this gas??. Any suggestion or previous experience? Regards Gabriel. |
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Craig Sawyers
The fact is that every knows that the original filling gas is no moreobtainable. Since I have access to a giant VanderGraf linear accelerator 20MeV,whichis filled with SF6 gas"Sulfur hexafluoride" to attain dielectric barrier, andthe SF6 gas has at 1 ATM 6 to 10MV/mts of breakdown, mean 2 to 3 times the airAlas no - there are two problems. First is vapour pressure at 20C is 10 atmospheres - so the probe explodes. Second is the dielectric constant (essential for correct probe operation) which is very different from FC114. Lots about this in the archives. Craig |
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Gabriel mendez
Hi Craig...what I know about this SF6 is that are stable in a open container and don't evaporate at room temp.
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The dielectric constant is not an issue since most gas have similar one..very near 1. The bad news is that I recheck and the gas available to me is now mixed with nitrogen,for cost reason,that is a new song! Regards Gabriel. --- In TekScopes@..., "Craig Sawyers" <c.sawyers@...> wrote:
The fact is that every knows that the original filling gas is no moreobtainable.Since I have access to a giant VanderGraf linear accelerator 20MeV,whichisfilled with SF6 gas"Sulfur hexafluoride" to attain dielectric barrier, andthe SF6gas has at 1 ATM 6 to 10MV/mts of breakdown, mean 2 to 3 times the airAlas no - there are two problems. First is vapour pressure at 20C is 10 |
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Peter Gottlieb
Look through the archives, that Freon is still available from some specialty chemical suppliers.
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On 12/22/2010 5:39 PM, Gabriel mendez wrote:
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Craig Sawyers
Hi Craig...what I know about this SF6 is that are stable in a opencontainer and don't evaporate at room temp.What it does in an open container tells you nothing about what it does in a closed container. From the Air Liquide website: "Vapor pressure (at 21 °C or 70 °F) : 311.83114 psi" for SF6 Which is 22 atmospheres. That is the pressure that the gas will be when in equilibrium with a liquid in a closed container at 21C. FC114 by comparison is 2 atmospheres at 21C. The dielectric constant is not an issue since most gas have similarone..very near 1.Yes, that is correct. But the pressure remains the seriously big issue. Craig |
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Tom Miller
How about Freon 11? BP is 23.7 C
Anyone have a chart of dielectric constants for freon gases?
Other electronic properties?
I have a 100 pound drum of F11. I don't have a P6015 HV probe
though. Maybe I should get one and try it.
Tom
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frasercastle
--- In TekScopes@..., "right_electronics" <right_electronics@...> wrote:
Gabriel, The following Tesla forum archive page may be of interest to you and other P6015 owners. http://www.pupman.com/listarchives/2003/June/msg00521.html It would appear that you would probably be wasting your time trying to recharge the P2015 probe without also replacing all the aged seals. 'Terry Fritz' stated that he used mineral oil as an alternative to a Freon based dielectric and had some success. Fraser |
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Gabriel mendez
Craig,some thing seems to be wrong with the pressure beheaviour of SF6, since is used in a several high voltage gear that not can handle the presure you mention,since they will work in extreme ambient temp..like 55°C or more!.
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I will do a little more research about,in particularly with nitrogen mix , which is what I can obtain. In other way...the metallic arms inside the probe form a shunt capacitor for a 100Moms resistor ,and add some cap to ground,obviously if we fill with silicone oil,such cap will be increased about 2,5 times....but...if we enclose the resistor/arms inside a small diameter tube filled with oil,then only this small diameter tube will contribute to an increase cap. They will look like cylindrical concentric capacitors,the small tube with oil,inside a large one (the bodie probe),with air between. The overal cap increasing will be less,I will try to do some numbers about. Just an idea to work with. Regards Gabriel. --- In TekScopes@..., "Craig Sawyers" <c.sawyers@...> wrote:
Hi Craig...what I know about this SF6 is that are stable in a opencontainer anddon't evaporate at room temp.What it does in an open container tells you nothing about what it does in a |
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SF6 is not used in an equilibrium state; there is no liquid present.
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It's been a long time since I worked around a Van de Graaf, but we used to evacuate the pressure vessel and then fill it with SF6 gas. I forget now, but I don't think the final pressure was much above atmospheric. It was high enough that we could use a leak detector on the seals though. Probably no more than 10 psi above ambient. Tank sparks were always fun when it broke down. I think we increased the pressure a bit when running near the max. We couldn't go too high since it increased the stress on the vacuum components. We'd pump that stuff out, compress it and liquify it for storage when we had to open the tank. That's where the high pressure values come in. On Thu, Dec 23, 2010 at 12:39:08AM -0000, Gabriel mendez wrote:
Craig,some thing seems to be wrong with the pressure beheaviour of SF6, since is used in a several high voltage gear that not can handle the presure you mention,since they will work in extreme ambient temp..like 55?C or more!. --
Paul Amaranth, GCIH | Rochester MI, USA Aurora Group, Inc. | Security, Systems & Software paul@... | Unix & Windows |
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--- In TekScopes@..., "frasercastle" <fraser.castle@...> wrote:
As the engineering manager of the 6015A project to redesign the probe to eliminate the Freon, I can tell you there is no simple substitute that will keep the 20 kV rating. Non gas materials such as mineral oil, (transformer oil), wax, silicone RTV, and "ozone safe" Freon liquids have significantly different dielectric constants that move not only the main comp value, but more importantly all the HF time constants in the comp box out of adjustment range. Redesigning the probe turned out to be a much larger effort than originally scheduled. Note however that the 6013 is essentially a 6015 without the float, and the HF time constants tweaked for the slightly different dielectric constant of air rather than Freon. It was rated at 13 kV, rather than 20 kV If your applications are within this voltage range, then consider readjusting your probe for using air. IMO, this is about the only way to preserve the usefulness of the probe. If you really need the 20 kV rms, 40 kV peak for your ap, go with the P6015A, and be prepared to pay the high price. In reality, the original comp box design of the non "A" probe included some T coil peaking and other strange topologies for a passive probe comp design. The individual time constants had a large amount of interaction. While with patience it can be tweaked to give a clean pulse response from a low impedance source, the comp design has resonances in the passband. They are pretty low Q, but remember most high voltage circuits have moderately high source Z, so any dip in impedance is liable to produce distorted waveforms. The P6015A has a decent comp box design, and the physical form factor is much more "scope friendly" as well. - Steve |
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Craig Sawyers
Craig,some thing seems to be wrong with the pressure beheaviour of SF6,presure you mention,since they will work in extreme ambient temp..like 55°C orI realise that - but it is introduced as a gas, not as a liquid and then allowed to come to equilibrium. Or a calculated quantity of liquid is added so that on evaporation a specified pressure is attained. I guess the same game could be played the P6015, but the beauty of the original stuff is that when you injected it from the can, it evaporated at a slow enough rate to displace (moist) air from the body before you screwed the end cap on. You can use the P6015 without voltage withstand gas, but the spec is downgraded to 13kV (and in fact is just the same as the P6013 in that mode). the metallic arms inside the probe form a shunt capacitor for aenclose the resistor/arms inside a small diameter tube filled with oil,then onlythis small diameter tube will contribute to an increase cap.Well, you can still buy the P6015A from Tektronix. This is a redesigned probe filled with silicone grease. Costs around $1800 direct from Tek. Craig |
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Craig Sawyers
As the engineering manager of the 6015A project to redesign the probe towill keep the 20 kV rating.Great to hear from the guy responsible for the P6015A! Wish I could afford one - but I was lucky enough to snag a P6015 with a can of FC114. The body and can live in the fridge to keep the vapour pressure low and prevent leaking past the seals. Craig |
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Gabriel mendez
Craig Sawyers
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Steve Paul Amaranth frasercastle Tom Miller Peter Gottlieb hpnpilot219 Hi fellows!!. In my opinion not matter which gas since all have very simmiliar dielectric constant. The point is their dielectric strength!. SF6 at 1 ATM has 2to 3 times the air have. SF6 is used as gas ,not in liquid fase. Is so heavy that you can fill the probe like water,see this link: http://www.youtube.com/watch?v=lpWjR8r_Uvc This video give a clear idea that if you submerse the probe,the SF6 will remove all air..like if submersed in water,just make the fill operation very slowly...I guess. --- In TekScopes@..., Peter Gottlieb <hpnpilot@...> wrote:
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Peter Gottlieb
How would one test if SF6 is a good gas for the probe?
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Assuming a good fill, I suppose one could test compensation to see if the probe could be fully compensated within range of the adjustments. But for HV breakdown? Wouldn't that be a destructive test if it fails? On 12/24/2010 11:39 AM, Gabriel mendez wrote:
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Craig Sawyers
Hi fellows!!.dielectric constant.Gabriel Well, if you think you have a solution why not try it and report back? Just don't kill or maim yourself. Craig |
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Gabriel mendez
What can make destructive spark is ..current/energy,not voltage,then a big series resistors should be connected in series with the probe.
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I don't know if this Sf6 will work,because no previous one has make this kind of proposal,in order to replace the 114 for the P6015. By sure the compensation adjustment not will be altered ,since the difference in dielectric constant is infinitesimal. As soon I obtain a sample of "pure SF6" the test will be made and post here of course. Regards Gabriel. --- In TekScopes@..., Peter Gottlieb <hpnpilot@...> wrote:
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Peter Gottlieb
If I had one to play with, I would use an ESD gun from work to test it. I also have access to SF6, although I would have to go to it at another facility.
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Now all I need is a 6015! On 12/24/2010 1:53 PM, Gabriel mendez wrote:
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Craig Sawyers
What can make destructive spark is ..current/energy,not voltage,then a bigkind of proposal,in order to replace the 114 for the P6015.Have you looked at Tek's patent number US 3,256,484 June 14th 1966, which describes both the details of the probe and the characteristics of 114? Craig |
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Gabriel mendez
Craig,thanks you very much about tek patent..is a tutorial on P6015,very useful,in special the distributed capacitance at main resistor ,which facilitate the calculation when filled with others..like silicone oil,since for the SF6 will be the same.
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If you are talk about the "destructive effect of discharged of input capacitance,this energy will be a mere 2,4 milijoules @40KV and 3pF. not Enough for such resistors ,if you consider that in case of spark ,it will be between the front wire resistor (not his body)and the ring,since this wire has more electric field because his small diameter. Regards Gabriel. --- In TekScopes@..., "Craig Sawyers" <c.sawyers@...> wrote:
What can make destructive spark is ..current/energy,not voltage,then a bigkind |
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Gabriel mendez
Craig..corrections!!
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"""it will be between the front wire resistor (not his body)and the ring.""" Must be corrected to: The front outer diameter of bell polished cap. Sorry. Gabriel --- In TekScopes@..., "Craig Sawyers" <c.sawyers@...> wrote:
What can make destructive spark is ..current/energy,not voltage,then a bigkind |
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