[GreenKeys] Was: TWX/TELEX now: Analog Computers

Fri Apr 16 04:57:29 EDT 2021

Steve,

Well in fact its generally not too hard to set up a simulation on an analog computer. The elements of the computer match the terms in the equations.

One  tricky bit is scaling the problem. Normally transistor computers are limited to +/- 10 volts, so if you are simulating something like a shell trajectory that travels several hundred meters you might set 1volt to be 100 meters.

Of course this then limits the accuracy of your solution. If you are calculating artillery ranges, you may not be accurate to hit a small target.

One reason that analog computers remained in use for a long time, was that they work in real time (or at some factor of real time, much faster for glacier movement, slower for an explosion)

When digital computers began to be used the programs often simply simulated an analog computer. You had a card for each module which listed the modules that formed its inputs.

Mechanical analog computers still boggle my mind. For a while I demonstrated the Hartree Differential Analyzer 

https://bollingtonscibar.wordpress.com/2014/10/15/hartrees-differential-analyser-an-electromechanical-computer/

and before that I worked at a tidal computation lab where I walked past this every day as I went to my office…

https://www.ntslf.org/about-tides/doodson-machine

more info here

http://www.bidstonobservatory.org.uk/tide-prediction-machines/

Dave

G4UGM

From: greenkeys-bounces at mailman.qth.net <greenkeys-bounces at mailman.qth.net> On Behalf Of steve bennett via GreenKeys
Sent: 16 April 2021 02:09
To: greenkeys at mailman.qth.net; John <John at tubetestingpros.com>
Subject: Re: [GreenKeys] Was: TWX/TELEX now: Analog Computers

Analog computers boggle the mind.

I have a hard time comprehending what it must have took to set up a simulation.

We are talking about non linear math so the levels of all the components had to be

brought to the desired state at the same time before hitting the go button.

All that and a model is only as good as the assumptions you used to build it.

I think digital computers and software engineering has made us all dumber.

I will get flak for saying that but I worked in computer IT for 26 years and trust me we are dumber. lol

I got out just in time to save my sanity.

-s

On Thursday, April 15, 2021, 08:37:57 PM EDT, John <john at tubetestingpros.com <mailto:john at tubetestingpros.com> > wrote: 

 You might be very interested in exploring "Analog Computers".  I've owned several, large and small.  They use known standardized components and voltage values to compute, and simulate, systems that vary over time.  

There is a niche for them yet today, even though the speed of even simple/cheap modern computers is now sufficient to model most things. Many industrial control system courses still have them in the labs.

However - if you have a grasp of the mathematics of what you are investigating (and it's a 'physical' system, like a weight on a spring in a viscous medium) it's trivial to "program" an analog computer to model that system, sometimes in real-time, and to make changes to system parameters (the mass of the weight for example) and have the results directly available, with no need to translate the model into some high-level language on a digital machine.

A lot of large-scale flight simulators used large analog computers to drive them.

Google "analog computer" to a deluge of info.

For a reasonably useful simulation and modeling program, see "Flowstone"

For the best open-source (free) modeling and simulation package out there, see "SciLab".

Obligatory Greenkeys:  RYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYFIGSBELLTRSCRLFCRLF

okay I feel better now.

Cheerz

John KB6SCO

Carson City

On 4/15/2021 4:00 PM, steve bennett via GreenKeys wrote:

In my first electronics class in vocational school the teacher gave us some analogy to explain a resistor.

A light bulb went off in my head and I added my own analogy for capacitor and inductor.

Teacher stopped me "not so fast son...you are taking it too far"

It wasn't until years later when I enrolled in electrical engineering I learned I was right all along and the vo-tech

teacher didn't know what he was talking about.

The math that describes the behavior of a capacitor is the exact same math that describes the behavior of a mechanical spring and the math that describes the behavior of an inductor is exactly the same math that describes mechanical inertia.

-Steve

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