Times change

[Harry Bloomfield]

40 odd years ago, some big (really big) variable speed DC motors I installed, came with a rather ridiculously precise spec., suggesting it needed to run at some silly full speed figure like 548rpm +/- 1 RPM. Checking with head office and the designer, they confirmed it had to be exactly so.

All we had at the time were mechanical tachometers, not very precise and no way to connect apart from to the side of a large coupling, so I set about designing something digital and entirely electronic, using an IR head. Work it did, very well and quite precise. It cost the company around £30 for the parts for me to build it, in my spare time. That was left with the company when I moved on.

A couple of weeks ago, working on the tractor mowers governor system, that specified a tick over speed and a full engine speed. I had no obvious way to measure its speed, so I began thinking shall I build, or just see what is for sale ready to use. Laser, ready to use, with guaranteed precision, in a nice protective carry case all for £7.03 and delivery within one month - no contest ;o)

Yes, I could have measured the ignition pulse period on my 'scope, or on my Marconi counter timer, but where is the fun in that when compared to a new toy?

[Tim Lamb]

In message , Harry Bloomfield writes

You have to wonder who determines these specifications..

As a sprog apprentice, I was sent out to an American air force installation near London to supervise test runs on a DC motor generator set.

The spec. called for the set to take over the load (comms of some sort) within 10mS! of the mains supply failing.

Needless to say 10mS could not be achieved. Simple reactance calculations of the motor field winding would have shown this.

The cure was a thumping great flywheel.....

[charles]

That's what was used in a telephone exchange I visited in the 1950s.

[Harry Bloomfield]

charles presented the following explanation :

This was three motors, driving three big pump sets, pumping from a reservoir, all remotely monitored and controlled by telemetry from the other side of a city.

[Brian Gaff]

I did a similar thing with a new fangled device called a hall effect sensor and a magnet glued to the spindle grin.

Not very imaginative and in those days simple pulse counters were el cheapo. Brian

[Andrew Mawson]

Back in the early 1970's I worked on the control computer (Ferranti Argus

500 with Argus 400 i/o) for Wiggins Teape's No 5 paper mill in Dartford. Under the raised control room was a motor generator set with a similar thumping great flywheel, to buy time for change over in the event of a power cut.

I had engineers who refused to visit the place as the girls on the paper cutting line were definitely not 'PC' and were known to literally remove visiting engineers trousers :) Talk about sexual harassment - it wasn't only the paper making process that made for a hot and steamy atmosphere !

Andrew

[Huge]

[47 lines snipped]

Tee-hee. As a student in the early 70's, during vacations I worked in WD & HO Wills tobacco factory (now a shopping centre) in Bedminster, Bristol. There were parts of the factory that some men were nervous about entering for the same reason!

ObDIY; I mostly worked as a fitter's mate. Great times.

[Lee]

Several members of my family worked there in the 70s, apparently the work's outings were legendary :)

Of course it's all gone and turned into housing now.

[Harry Bloomfield]

Lee explained on 17/08/2017 :

What was really appreciated by me, was the fact that all of that work I did back then, will still be there and very much still in full use.

[Harry Bloomfield]

Brian Gaff formulated the question :

From what I remember, I used a proper crystal controlled counter timer circuit, interfaced to an LED display and a combined IR transmitter / receiver module. With the latter bolted on a bit of broom rod, so the shaft could be reached. It focused over just a few inches, so had to be close.

Shaft was polished with a bit of emery, then a bit of black tape added to create the pulse.

[Tim Lamb]

In message , Harry Bloomfield writes

Well the Clywedog reservoir dam is still standing. Now you have reminded me, I wonder how the Germanium transistors fitted in the control gear are holding up!