SCADA (was Re: Help to identify a computer?)

Tony Duell ard at
Sun Feb 18 20:07:25 CST 2007

> On Sun, 18 Feb 2007 22:46:57 -0800, Brent Hilpert wrote:
> >"In even later years, solid-state rectifiers of sufficient capacity for the
> >traction power industry were developed, and substations became no more
> >exciting than giant computer chips."
> Now there are fighting words. I expect this group would find a giant 
> computer chip of great interest ! 

I don't find large chips to be of much interest. Now large boards of 
small chips are a differnt story :-)

> Thanks for the subway link, and to keep things on topic, the IBM 370 
> family of mainframes used a MG 
> (motor genertaor) set to convert the 60hz power from the mains to 3 
> phase at 400Hz to allow more efficent 
> conversion of power in the internal supplies. Both smaller 
> transformars and much smaller filter caps were 
> needed to convert and smooth the 400hz to DC.

I believe (military?) aircraft used 400Hz-ish supplies because they could 
then use smaller (and lighter) transformers and smoothing capacitors. It 
can be a problem for the military radio enthusiasts who want to power up 
such sets now.

And of course it's one advantage of the modern SMPSU. The transformer is 
much smaller than a 50Hz (or 60Hz) transformer of the same output 
ratings, and the smoothing capacitors are smaller too.

> In fear of sliding too far back on topic :-) 
> I will point out that the telephone system uses 90v 30hz as the ring 
> signal because it worked so well with 
> the mechanical bells used in the early phones.

Over here I think it's officially 25Hz, but for much the same reason. 
Medium and large telephone exchanges produced that supply using a 
motor-generator set running from the (50V DC) lead-acid battery that 
powered the rest of the exchange. Small private exchanges produced it 
from the mains using a resonant transformer/capacitor circuit fed with 
half-wave rectified mains (I have one of the ex-GPO converters somewhere).


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