Love the visual paradox which helps me to better understand something not so intuitive to me when it applies to gravity.
Closed loop perspective:
Imagine walking clockwise on this staircase. With each step gravity would be doing negative work on you. So integrating the work along your full circular loop, the total work gravity does on you would be quite negative. However, that's an integral in a closed loop, so the fact that it's nonzero must mean the force acting on you cannot be conservative.
Path independence perspective
Imagine walking from the tower on the right corner to the left corner. If you get there along the clockwise path, gravity does negative work on you. If you get there along the counterclockwise path, gravity does positive work on you. Since both paths start and end at the same point, path independence fails, so the gravity force field cannot be conservative.
Gradient perspective:
In the real world, gravitational potential corresponds with altitude, because the work done by gravity is proportional to a change in height. What makes the Escher drawing striking is that the idea of altitude doesn't make sense. Many steps "up" with no steps down can lead you back to the same point. This corresponds with the fact that there is no potential function UUUU such that ∇U\nabla U∇Udel, U give the gravity field.
source:
https://www.khanacademy.org/math/multivariable-calculus/integrating-multivariable-functions/line-integrals-in-vector-fields-articles/a/conservative-fieldswww.math.harvard.edu/archive/21a_summer_10/handouts/week5.pdfwww.phys.utk.edu/daunt/EM/PDF/SJDLecture29.pdf (attached slide source)
Lots of tying up loose ends. So as not to inconvenience my better half any further - I built a stand out of scrap wood for the spectrum analyser monitor and HD camera. I can now get all vehicles back in the garage and continue testing. 
Shouldn't one of those vehicles be a 1982 DeLorean?
I want to build a high voltage dummy load that I can swap out the frustum for. My magnetron is 600W
Would a couple of these in parallel work? http://www.digikey.com/product-detail/en/FVE030020E10R0KE/FVE300-10-ND
http://www.vishay.com/docs/31842/fve.pdfTheir datasheet shows a dielectric voltage of only 1000 VAC... I believe the magnetron is a ~4KV supply?
So definitely a "no" to simply grouping them in parallel. In theory you might be able to have 4 or 5 in series (5 to give at least some margin)... but to restrict the current you'll need something several orders of magnitude larger than 10 ohms.
In summary, these are are
not the parts you are looking for.
I want to build a high voltage dummy load that I can swap out the frustum for. My magnetron is 600W
Would a couple of these in parallel work? http://www.digikey.com/product-detail/en/FVE030020E10R0KE/FVE300-10-ND
I recommend you not use these.
The data sheet indicates they are wire wound resistors. They will have significant inductance (and parasitic interwinding capacitance) that will make them a poorly behaved load at 2.45 GHz. And there's the question of whether their voltage rating is adequate even under well-matched conditions, which these won't present. You won't have a stable absorber and it could arc. Either will first displease your magnetron, then you.
I've used dummy loads at 2.45 GHz that consisted of a blind, flanged stub of WR284 waveguide, inside of which was a block of Teflon with a passage through which water circulated. The circulating water was a great absorber and took the full 5kW generator output with no drama. These aren't hard to build, especially if you can snag a length of flanged waveguide somewhere. The Teflon machining can be done with a saw and a drill press.
Another dummy load I used in a pinch was a cotton bag full of cheap, coarse silicon carbide abrasive particles. SiC is a good absorber at 2.45GHz (and at 915 MHz). This can only work for a limited time because the SiC abrasive gets hot. I used it when I needed a good microwave absorber in a plasma CVD chamber so I could measure and tune out reflections from the hardware absent a plasma. It took less than 30 sec to get the data, and the ~5 lbs of abrasive was hot but not difficult to handle afterward. This was with a 30kW 915MHz source.
Ideally, what you want is power film resistors such as those used in Bird dummy loads and the like. Not being wire wound, these have very low inductance and parasitic capacitance. They are much closer to a stable, purely resistive load. Ebay is a potential source. Most of these are coaxial input, so you'll also need a waveguide adapter that will accept your magnetron and give a coax output to the load. I've found these on Ebay as well.
I want to build a high voltage dummy load that I can swap out the frustum for. My magnetron is 600W
Would a couple of these in parallel work? http://www.digikey.com/product-detail/en/FVE030020E10R0KE/FVE300-10-ND
What if you put a sealed container of water inside the frustum?
Maybe. Water is a good absorber. Polyethylene would probably be a good container material.
Essential safety matters: make sure the container can easily open up to relieve pressure if the water boils, that the frustum isn't gas-tight for the same reason, and plan it so water can never reach electrical parts...like the magnetron HV leads
...
I want to build a high voltage dummy load that I can swap out the frustum for. My magnetron is 600W
Would a couple of these in parallel work? http://www.digikey.com/product-detail/en/FVE030020E10R0KE/FVE300-10-ND
Your maggie output will be RF which ideally is matched to the input impedance of your frustum which is a function of your feed and circuit Q. Think of the frustrum as a parallel RLC tuned circuit at resonance which is a high impedance. You can probably use a water resistor if you are faraday shielded as not all of the rf will be thermally dissipated. See
http://home.earthlink.net/~jimlux/hv/rwater.htm for design info.
I want to build a high voltage dummy load that I can swap out the frustum for. My magnetron is 600W
Would a couple of these in parallel work? http://www.digikey.com/product-detail/en/FVE030020E10R0KE/FVE300-10-ND
If your goal is to optimize the power supply performance without actually powering the maggie, you should consider that the power supply is probably designed to produce about 1000W. If it is running about 4KV, then you need a 26 kilohm load capable if dissipating 1KW (P=E
2/R). A good way to build that is to put 10 100W 2.6K resistors in series (something like
these). That way, each one only has a 400V working voltage. You will probably find that these beasties are expensive (like $45 each), so your best bet is to scrounge around in your local electronic surplus outlet.
I would ask first what are you trying to measure?
Shell
The goal is to measure the heat expansion of the HV magnetron leads without RF in the cavity. If there is a thermal component to the wires, then I figure that is the best way to characterize and subtract it from any real thrust.
I suppose I could just flip the wires to the other side of the torsional pendulum and see if the effect is reversed.
I would ask first what are you trying to measure?
Shell
The goal is to measure the heat expansion of the HV magnetron leads without RF in the cavity. If there is a thermal component to the wires, then I figure that is the best way to characterize and subtract it from any real thrust.
I suppose I could just flip the wires to the other side of the torsional pendulum and see if the effect is reversed.
Good idea.
Am I correct that your thermal video shows only a rise of ~2C over ambient on the wires?
Shell
Added: or you could bind the wires to keep the thermal expansion of the wires to a minimum. Get some tape to tape them down.
Am I correct that your thermal video shows only a rise of ~2C over ambient on the wires?
That is what I saw ~2C, but that was after power off. I would like to get IR while power is on. And there is a setting on the IR camera for close up views - otherwise the IR doesn't match up with the camera overlay. I need to make sure that is activated.
I want to build a high voltage dummy load that I can swap out the frustum for. My magnetron is 600W
Would a couple of these in parallel work? http://www.digikey.com/product-detail/en/FVE030020E10R0KE/FVE300-10-ND
Re-reading your post this morning, I see you may have been asking about a dummy load for the magnetron HV power supply, not the magnetron output. Sorry if I missed your meaning.
If you want a dummy load just for the HV supply, the wire wound resistors will be fine at the supply's 120Hz half wave output. The only other question is resistor voltage rating with respect to interwinding breakdown. I'd experiment. Put them inside a grounded metal perf box, energize them and look for arcs/smoke, etc. The pic in the data sheet looks like a coarse winding pitch, meaning there's significant insulation between adjacent winds. That's good for preventing breakdown.
I want to build a high voltage dummy load that I can swap out the frustum for. My magnetron is 600W
Would a couple of these in parallel work? http://www.digikey.com/product-detail/en/FVE030020E10R0KE/FVE300-10-ND
You will need to connect resistors in series, not parallel. Surface leakage currents need to be minimized. Also a wirewound resistor may have too much internal leakage current. I have noticed that some resistors become open-circuited when high voltage is around. It is a static electric effect. You should avoid wirewound, carbon composition, carbon film and any resistor that looks like it is economy grade. Also don't use high value (> 1 Meg) resistors. Use a lot of resistors wired in series inside a plastic box - nylon, teflon, or thick plexiglass. Any metal near the resistors is a possible leakage path. If you build it in a plastic box you won't have to use ceramic stand-offs to support the resistors. Another option is to press solder posts into a sheet of FR4. Solder the resistors between the posts. You can pack a lot of high wattage resistors into a small space and still have good separation that way. I have no idea what power level you are aiming for. 200 Watts may work for a short test = 100 2 Watt resistors.
I want to build a high voltage dummy load that I can swap out the frustum for. My magnetron is 600W
Would a couple of these in parallel work? http://www.digikey.com/product-detail/en/FVE030020E10R0KE/FVE300-10-ND
Re-reading your post this morning, I see you may have been asking about a dummy load for the magnetron HV power supply, not the magnetron output. Sorry if I missed your meaning.
If you want a dummy load just for the HV supply, the wire wound resistors will be fine at the supply's 120Hz half wave output. The only other question is resistor voltage rating with respect to interwinding breakdown. I'd experiment. Put them inside a grounded metal perf box, energize them and look for arcs/smoke, etc. The pic in the data sheet looks like a coarse winding pitch, meaning there's significant insulation between adjacent winds. That's good for preventing breakdown.
Maybe I'm missing something here but the wires to the magnetron that are twisted together that he wants to measure are ~4,000V.
The resistors will make magic smoke if you put them in this line to replace the magnetron.
Shell
I want to build a high voltage dummy load that I can swap out the frustum for. My magnetron is 600W
Would a couple of these in parallel work? http://www.digikey.com/product-detail/en/FVE030020E10R0KE/FVE300-10-ND
Re-reading your post this morning, I see you may have been asking about a dummy load for the magnetron HV power supply, not the magnetron output. Sorry if I missed your meaning.
If you want a dummy load just for the HV supply, the wire wound resistors will be fine at the supply's 120Hz half wave output. The only other question is resistor voltage rating with respect to interwinding breakdown. I'd experiment. Put them inside a grounded metal perf box, energize them and look for arcs/smoke, etc. The pic in the data sheet looks like a coarse winding pitch, meaning there's significant insulation between adjacent winds. That's good for preventing breakdown.
Maybe I'm missing something here but the wires to the magnetron that are twisted together that he wants to measure are ~4,000V.
The resistors will make magic smoke if you put them in this line to replace the magnetron.
Shell
Actually the $moke is more likely to come from the transformer if the load does not have the right resistance.
If you consider the supply is delivering .25 A @ 4kV, a load resistance of 16 kOhms would substitute for the magnetron. If you used 100 X 180 Ohm 2 - 10 Watt metal film resistors all wired in series that should work for short duration tests. Mount them on an FR4 card on standoffs inside a sealed box. A metal box is ok if everything is rigidly mounted and well insulated.
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If you consider the supply is delivering .25 A @ 4kV, a load resistance of 16 kOhms would substitute for the magnetron. If you used 100 X 180 Ohm 2 - 10 Watt metal film resistors all wired in series that should work for short duration tests. Mount them on an FR4 card on standoffs inside a sealed box. A metal box is ok if everything is rigidly mounted and well insulated.
The heating of the lead wires are due to current through them, not tension. So if you want to get the component of measurement (assuming linear additivity of contributing components) due to this thermal effect alone it's best to avoid heating anything else by dumping hundreds of W to some dummy load, because at same dissipated power the dummy load will have a different impact on measurements : we won't know if (how much of) the measure is different because of a thermal effect on the wire or different thermal effect of the charge at the end of the wires.
I think it would be better to mimic the same
current pattern (if it is known, even only roughly) in the wires only, by short circuiting the 3 wires (where they normally feed the magnetron) and feeding them by a current generator circuit (in place of feeding them with the normal output of the HV power supply). There is a little complication because there is 3 wires so 3 currents to set but I'm sure this is doable with low power resistors
and not involving high tensions.
Magnetron power supply off (not wired), magnetron off (not wired), same wattage dissipated in wires only, check with thermal measurements that wires heating is comparable, read measurements induced by this heating
alone. Only constraint, devise and build a specific 3 wires current generator. How much of the kW or so that goes through the wires actually is dissipated in the wires ? A few watts at most : this is the required power for this current generator. If someone can tell approximately the 3 intensities (in A or mA) that go through the 3 wires and orientations with clear labeling, I or anyone knowing Ohm's and Kirchhoff's law can design the circuit powered on any low power source of tension at 12VDC or so (wild guess).
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