Analogue computing

[jim_beacon]

Something I missed from the list of bits.

A couple of years ago, I acquired a number of small plug in units, which had an octal plug on the base, and 2 B9A sockets on the top.

Further research told me they where Philbrick K2W op-amps, intended for analogue computers. You can see one here:

http://dcoward.best.vwh.net/analog/

Anybody had any experience of this branch of computing?

Jim.

[evingar]

Anybody had any experience of this branch of computing?

Hi Jim

Not of the vintage you are talking about, but my HNC course in the early 80s still included a small module on analogue computing, basically how you could perform the basic functions, adding, multiplication and calculus etc (strictly silicon op-amps though!). I think this was a left over from former times. We also had a module on valve amplifiers. Both modules disappeared when the course was re-jigged a year later, so I guess I was in at the end of an era.

Chris

[peter_scott]

In my vacations as a student back in the late sixties I
had involvement some electro-mechanical analoque computers. I was never given sufficient information to enable me to understand the things but
they consisted of many interlinked servo-motors coupled
through various fancy gear mechanisms. The whole being compressed into a metal box about one cubic foot.

Peter

[GMB]

I encountered analogue computing at school in the late 1960's or maybe early 1970's.

A previous generation of boys had started building a copy of the " Practical Electronics " analogue computer, and then left.
I was asked to finish it and make it actually work. My enthusiasm for working on someone elses project was enormously boosted by being informed that this activity would take place during " games " periods and so I would be excused from having to squelch about in the freezing mud whilst being crushed, kicked and generally shouted at by keener rugger players.
The project was almost finished, and although it didn't seem that there was much to do to get it all working, it strangely took a long time to complete.

My main discovery on this was that you needed a lot more of it. It had just a few op-amps and one integrator.
It was entirely built from discrete transistor technology - and so its main problem was temperature stability.

I have run into valve analogue computers too. My lasting impression of one was walking right through the computer of an early flight simulator. I can't remember what aircraft it was for - an early jet airliner I think. The thing that I really remember, apart from the heat, was that the valves were all in parallel pairs so that it didn't stop working just because a valve heater burned out. I noticed that quite a few valves had failed - but no-one seemed to be worried by this - and the simulator definitely still worked.

The earliest analogue computers were for gunnery calculations of course.
I'd love to know more about the amazing and very secret one that was operating during WW2. Did you know that there was a computer controlled battery somewhere near Dover that was shooting down German V1's, all done by computer? These guns actually fired shells containing a valve-based proximity detector!!! The computer's input was direct from pots attached to the usually visual sights used by the Observer Core. It calculated the planes trajectory and automatically aimed the guns. It just had to get the shell pass reasonable close to the plane and if the valves in the shell were still working then they did the rest. Apparently it worked really well.
Amazing technology!

[ppppenguin]

AFAIK there was only 1 valve in the shell. It was part of a proximity detector that relied on the capacitance between the sheel and target to change the frequency of an oscillator (or maybe unbalance a bridge) which then detonanted the shell. The great thing about a proximity detector is that near misses will still damage the target.

Although it was fast the V1 was actually a very easy target to for the gun laying radar to predict since it flew in a straight line.

There's a lot more on this subject in " The Invention that Changed the World " by Robert Buderi.

[AC/HL]

They're also used in the simpler auto-pilots for light aircraft, or at least they were when I maintained them going on for 20 years ago. Most will still be in use as avionic equipment is expensive, so is kept maintained longer. I handled the odd valve transceiver (Nuvistor)

[Ed_Dinning]

Hi Gents, Teledyne Philbrick were the big guys in this field, I may have somme of their app notes if anyone is interested. The man who knows all about this is Bob Pease, a nat semi staff scientist. Try putting his name in google ans see what appears, he's usually ameniable to e-mail and runs a column in one of the professional mags. Send me a PM if you want any more details.
Ed

[newlite4]

We still use analog computers at the University of Bath. They are used for servo control teaching in the Engineering faculty. There are seven racks, each containing op-amp integrators and differentiators with summing junctions, a power amplifier and motor/generator set with position pot. In my role as lab technician, I have kept these up to date over the past 24 years. Nowadays, we have a digital system that works alongside the analog racks for comparison purposes. We no longer use analog computers in the research areas, they used to be used extensively for hydraulic control simulation. The last one I installed was over 20 years ago, this was a Solartron HS27-3d made in 1969, it was about the size of a small car .
Neil Deacon

[zebedee]

Back in the Sixties I built (not designed) a purpose built analogue computer for Appleby Frodingham steelworks in Scunthorpe. As a red hot billet of steel was fed towards the rolling mill, the length was measured by a series of photocells.
The approximate elongation factor was pre-set on rotary switches, so the computer calculated the final length and set the flying shear to cut the steel into lengths required by the customer. For the final cut the shear was set to the maximum length that the customer would accept.
The computer was built into a 19inch rack about six foot high and consisted largely of multi tap toroidal transformers, Paington winkler rotary switches for setting up the customer's requirements and a large 1KHz (valve) oscillator to drive the transformers and amplifiers etc.

The unit was designed and built in the United Steel Companies Department of Operational Research and Cybernetics in Sheffield, where I worked for many years before United Steel became British Steel.

To think that today the same job could be done by a PIC with a few lines of code!

[tis your junk]

My introduction to computers was via Analogue computing!

Like others on the list I picked up the Practical Electronics project that the previous years 5th year had started but could not get to work. I think they must have had better skills in wood work etc because the cabinet was beautiful, the electronics less so. Following a few elementary corrections to the amp boards and a complete rebuild of the PSU ( less said about that the better) it worked very well.

I can remember doing calculations on a ball being thrown into the air and finding out how far it would travel etc. In the sixth form the following year I studied computer science and could not believe how much programming one had to do to repeat the calculate using a digital computer. However the computer science teacher (a lady) was significantly intrigued to ask me to teacher her about analogue computing. I think we also demonstrated it at one parents evening.

Looking back on it, it was a great learning experience, especially having the "buy in" from the teachers. I am also amazed, given the current regulations that we were allowed to do such things, 5th formers building mains driven PSU etc.

However I for one am glad I had the chance.

Tis Your Junk

[flyingtech55]

Apparently the human brian is mostly analogue. It has no actual system clock as far as is know.

TimR

[petermeachem]

Sorry to be a bit late here, but I've only just joined.

I used a TR48 extensively at university. http://dcoward.best.vwh.net/analog/eai.htm
As someone has said above it was brilliant at things like hydraulic servo research. It was so quick and easy to change parameters. You could also hook it up to lumps of hardware fairly easily.
I spent ages trying to make a hybrid computer by using it with a Honeywell H316, but the multiply on the Honeywell was hopelessly slow.
I also spent years working on flight sims and saw the last analogue sim that Link Miles made, at least for a commercial airliner. It was dreadful, unreliable and terribly temperature dependent.

[evingar]

Apparently the human brian is mostly analogue.

We've got a Brian at work, but I don't think he's human. He could be analogue though