[vcf-midatlantic] vacuum tube computers, was Re: Museum Report 2017-11-26 November 26, 2017

David Gesswein djg at pdp8online.com
Mon Nov 27 07:55:03 EST 2017


On Sun, Nov 26, 2017 at 10:34:27PM -0500, Jeffrey Brace via vcf-midatlantic wrote:
> >
> > I'll jump in since I do have some interest in the education side
> > though this isn't one of my better areas of expertise. Others
> > will probably correct.
> >
> >
> Thanks for the for the explanation David! Let's start with the most common
> question that everyone asks: "How was this computer used?", "What could you
> do with this computer?", "What was it capable of doing?".
>
I don't know enough history on either of the specific computers we have to 
comment on how they were used. I can only comment on the general class.

Hopefully you can pull out what you need from this.

The what was is capable of is solving systems of differential equations.
Since since teaching calculus probably won't go over well just having
the equations for some problem and saying the equations represents 
the example (bouncing ball, car spring & shock absorber
etc) may be all that can be done. The complexity of equations that
can be solved  is limited by how many hardware block (integrators etc) the 
analog computer has.

http://chalkdustmagazine.com/features/analogue-computing-fun-differential-equations/
https://www.nsa.gov/news-features/declassified-documents/tech-journals/assets/files/why-analog-computation.pdf

The power is that many useful real processes can be transformed into that
type of equations.  Physical motion, chemical reactions, aircraft flight,

The analog computer can solve the equations standalone by setting the initial
conditions and then showing how they progress with time. For example
the bouncing ball say you scaled 1V = 1 foot you start with 5V so ball
dropped from 5 feet and can watch the height of the ball with time.

You could also feed in an analog signal representing stimulus such as
for the suspension example a signal representing the bumps in the road or
for flight gusts etc perturbing the flight.

Sometimes you just want the final state of the system so would let it progress
until you get a stable answer and then read off the voltages and then
convert them back to the original units. Other times you
want to watch what happens over time. You can scale time also so the
time "running" does not have to be equal to the physical problem. For
viewing the time history an oscilloscope could be used and I think I
remember a CRT in the Philbrick so it likely was used like an oscilloscope. 
It was said that our Philbrick had a plotter. That directly generates a 
hard copy graph of the value vs time. Some were chart recorders which can 
plot multiple values at once. Don't know what type we have.

The analog computer my mother worked with modeled the flexural modes of
vibration and critical frequencies of complex mechanical systems like ship
hulls and shipboard machinery assemblies.  




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