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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
EDIT: (UPDATE: 15.4pF + 15.4pF = 7.0pF !!! (seriesed) Capacitience Problem SOLVED! And thier rock stable too. I belive the 7.7pF vs 7.0pF discrepency is due to the leads' capacitence and nulling. I think its fine as long as the two inpdependent capacitences are close/exactly the same. I have class now, will be back to harmonize the math later.) All of this was later proved wrong, the capacitences do not divide evenly, due to "Molar-Coulomb charging" on dissimilar surface areas. The steel tube at a half length has twice the SA of the full copper tube.
The tube with insulating fins.
FR4 composite fins, nevermind the scorched carbon. Ths is a non-fucnctional mock-up.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Proud Mary wrote ...
Great too see it all going swimmingly, Patrick!
No! I managed to find a new crisis to play with. Their sharing 1.1pF's THROUGH the tube! Damt it thats why the should be 7.7pF is actually 7.0pF, dam it, dam it, dam it.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Patrick wrote ...
Proud Mary wrote ...
Great too see it all going swimmingly, Patrick!
No! I managed to find a new crisis to play with. Their sharing 1.1pF's THROUGH the tube! Damt it thats why the should be 7.7pF is actually 7.0pF, dam it, dam it, dam it.
It's always reassuring to meet fellow OSFTSB Club members.
(One Step Forward, Two Steps Back)
Club motto: In this disaster, business is always round the corner
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
[Gen 4, Type 3, Mod 40, Rev H, Ver 2.0, Attempt 9] for HV O-scope Probes, Has failed. Moving on to : [Gen 5, Type 3, Mod 50, Rev H, Ver 2.0, Attempt 10] (new cap leafs like the Tek 6013A will be looked at)
Previous attempt failed due to capacitence dividing unevenly, molecular oil (single charge per mole) added charge (Coloumb) which pushed the series capacitors division off ideal.
(From above post)
Patrick wrote ...
EDIT: (UPDATE: 15.4pF + 15.4pF = 7.0pF !!! (seriesed) Capacitience Problem SOLVED! And thier rock stable too. I belive the 7.7pF vs 7.0pF discrepency is due to the leads' capacitence and nulling. I think its fine as long as the two inpdependent capacitences are close/exactly the same. I have class now, will be back to harmonize the math later.) All of this was later proved wrong, the capacitences do not divide evenly, due to "Molar-Coulomb charging" on dissimilar surface areas. The steel tube at a half length has twice the SA of the full copper tube.
The tube with insulating fins.
FR4 composite fins, nevermind the scorched carbon. Ths is a non-fucnctional mock-up.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Here is a new source: ]hv_chap6.pdf[/file] Look at page 7, Fig 6.12(b) the conic-axial shield is strikingly similar to the NorthStar VD series, with those external grading rings tapered towards each other.
in the pdf the "cone" seems to make more capacity with the narrow end near the resistor, and less capacity is made as the taper expands wider, thus there would be less voltage across the high capacity side(closest), while more voltage across the lower capacity rim (farthest). Thus the unwanted stray capacity along the length of the resistor is in series with the deliberate capacity of the cone, and since the magnitudes and directions of the currents are opposing each other, the stray factors do not inluence the High freq Ac properties of the resistor. I think the e-field would be calculated as a derivative? or maybe a differential.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
New sources for oscilloscopes:
Time Domain, Rise time, related math.
Basic Probe types, considerations, limitations.
]n2771-92000.pdf[/file] Agilent N2771 Hv Probe.
Here's my newest problem: if the agilent N2771 Probe is 100Mohms in series with 1pF, and rise time = 2.2RC, then I get 220 uS! (it should be 7nS.) Which equals a probe with 4.5kHz of bandwidth, yet they claim a 50Mhz BW. What am I doing wrong?
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
Hi Patrick I don't mean to be impertinent but what exactly are you measuring? Pulse, ac, dc, decayed, what accuracy ppm, pulse duration, ect. At work when we build probes they may be built for what we are going to look at. If you intend to look at a broadband of what ever it will be harder to build a probe than if it was narrowed. mabe you will need a compansation box.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
teravolt wrote ...
... I don't mean to be impertinent...
Please dont hold back, I need as much input and verification as possible. (Even if your a communist from Berkely )
My Project Concept Design and purpose has the minimum requirements of :
Being able to measure sqaure waves from ferrite and other SMPS components, CW's...ripple on HV caps, and similar. --Square wave of 100kHz at High resolution. (10X the sample rate of a 98% amplitude sine wave BW) --Square wave of 500kHz at lower resolution. (but at 98% of amplitude, thus far away from -3dB) * I need to be able to resolve / detect on 1uS to 500nS abberations.
Given the following thoughts:
Since a BW of 4X faster (and less) than the wave being measured would yield a functional/trouble shooting aproximation. While a BW of 4X and greater would be a high accuracy characterazation. I will choose 5x, since the wave form in terms of Absolute magntude of voltage, and arrival/duration time will be used in deriving complex math for Ph.d. research. (i.e. I will use instaneous V x I @ T, integrating area under the traced curve to determine average power applied during each 20uS pulse)
I am trying to specify the reqiurements, but constrain them to what is needed and adequate. I would also like to have the power load drawn at High freq to be less than 10W if possible, Im still trying to figure out how to avoid derating (and loading) at High Freq. Impedance is a consideration, but i will be making measurements on a HV HF source and load pair operating at 100-500 watts, mostly. So 10W consumed will likely not burden the measurement displayed too much.
I believe the following is how I can justify spec'ing the probe, without magic numbers pulled out of the ass.
Soo... using the log properties, the desired ratio of "Wave freq to probe/O-scope BW" 20 Log (Vin/Vout) = 20 Log 0.98 = -0.175 dB 0.2 = BW 5 times faster than the signal speed = 98% signal amplitude displayed on screen. BW = 100 kHz x 5 = 500kHz x 10s/s = 5Mhz Rise Time = 0.35 / 5 Mhz = 70 nS
So to start with for the first generation I think a BW of 5Mhz, and a rise Time of 70 nS will be suffcient.
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High voltage probe for O-scope, 1 of 2, ( DEVELOPMENT ).
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