Tube simulator

Today's equivalent would be one of those very expensive charged-particle tracer programs, run in monte carlo mode. *Very* compute intensive!

Another handy analog computer was teledotos paper, a mildly-conductive carbon-impregnated paper. It was handy for calculating the sheet resistance of arbitrary shapes, and electric field distributions. The IC design guys used to use it.

I wish there was an affordable (as in free?) FEA program that would do the equivalent sheet resistance calcs. That would be handy for a lot of electrical and thermal situations. I tried adapting ATLC to do it, but it didn't work very well.

Trampoline sex?

John

McMaster.

John

From

Back in 1948 Robert Heppe of Fairfax, Va., was a freshman electrical engineer at the Queens, N.Y., plant of the Sylvania Electric Products Company. Heppe, assigned to assist in the design of vacuum tubes, found the process onerous. The problem was that one had to specify the size, shape and placement of the grids and beam-forming plates on paper. The design was then manufactured in the form of a single tube and tested. This could take several days. His supervisor, Gerald Rich, improved efficiency by suggesting a certain analog gadget.

The gadget consisted of a rubber sheet, a dowel, some plywood and several boxes of toothpicks. The rubber sheet clamped into a large ring represented the tube cross section magnified many times. The cathode was a wood dowel poking up in the center of the sheet. Arrays of toothpicks represented various grid designs. Negative grids tented the sheet up from below; positive grids depressed the sheet from above. Other aspects of tube geometry were captured by plywood shapes also imposed from below or above. Electrons pouring from the cathode were simulated by slowly emptying a can of BB's over the dowel. "It can be shown," writes Heppe, "that the slope of the rubber in such a gadget represents the electric field, and the height represents the voltage in the space between the electrodes.... The BB's rolled down the sheet [as in] a pin-ball game, some collecting at the plate, some at the positive grids. If we didn't like how many arrived at the various electrodes, or which way they went, we could move things around, change sizes, etc., and try it again." Promising configurations were embodied and tested in real tubes.

poles

Where can I buy/get a rubber sheet like that? I interpreted the description to mean a fairly thin sheet with some elasticity, but thicker than balloon material, although they don't specify.

"Dental dam" comes in relatively small squares, but it might do what you want. Google gives

Matt Roberds

Since I have to admit that I've met a few of the kinky crowd over the years - try this one for size !

Graham

years - try

That would make it very easy to smother someone without leaving any marks. I wonder if the coroner would find plastisizer residue all over the body.

I think i remember that Don Lancaster seems to have a scheme using Psotscript as the main processor to (visually) solve equi-potential fields and the like.

The math is actually simple. What's nasty, at least to me, is setting up the geometry entry/display/edit stuff. I guess a screen full of colored (according to conductivity) boxes/pixels would do, with some of them being passive resistors and some being forced potentials.

ATLC uses .bmp files, and allows you to create them with Paint or whatever. I guess that's the easiest way to go, but it's fairly awkward in practice.

John

I did not read much of DL's PostScript methodology, but it seemsd that useage was not complicated. It is at least worth looking into...