The future: DC mains

[Ian Jackson]

And transformers don't need as much iron, so are smaller and lighter.

>

[Ian Jackson]

In message [e-mail], Scott [e-mail]> writes

I once understood that synchronous electric clocks could be fast or slow, but at 8am the mains was supposed to have had the correct number of cycles in the previous 24 hours. Is/was this ever true? At the moment, the mains is running a bit fast (and I see that wind is only

0.89GW!).

[Andy Burns]

AFAIK, it was and still is true, that there should be 4320000 mains cycles per day. Maybe this chap counts them?

[zall]

Nothing odd about it, that avoids having to synch the frequency of the UK service with the european services.

[Scott]

Why 8 am though? This would be a difficult time to recover a shortfall, during the morning peak. I was told that the correction took place during the off peak.

[Roger Mills]

FWIW, it appears that the Yanks use AC for electrocuting people in their electric chairs.

[Peter Able]

Even when a TV had a tuner - overwhelmingly likely to be a turret tuner

- there was still the issue of your local transmitter frequency. Turret tuners had 13 positions - but rarely 13 "biscuits" fitted.

Talking of safety, Turret tuners loved to hack into TV engineers' fingers. Far worse than the occasional zap!

PA

[Paul]

Mains is supposed to be plesiochronous with the atomic clock network. A grid counts cycles, for the purposes of maintaining legacy analog and legacy digital clocks.

It's possible for a grid, to be perpetually slow, and not be able to make up the cycle count. This isn't a wand-waving job, it takes an effort to maintain the clocks this way.

Delivering power has priority over cycle accuracy. If the right conditions are not present on a grid, to inject cycles, then it simply won't happen. It's possible the clock corrections are done later in the day, rather than at 2PM.

*******

A GPS gives position information, but it also delivers accurate time. If you need to discipline a time-keeping device, GPS is one way to do it.

The LF transmitters offer a second way to do it (this is for the clocks that have the radio receiver with tiny ferrite antenna inside them -- the ferrite material for this, is made in Russia).

You can beat your local oscillator clock, against a HF radio reference. But that isn't all that good of a method. I had an oven-stabilized 1MHz clock, tuned by listening for a beat note on a shortwave radio. You can use that, for getting the quartz oscillator reference "in the ballpark".

Even Cesium or Rubidium references, are GPS disciplined, the commercial ones. And references like that can be obtained for around $1000 or so, whereas years ago, they were quite expensive. We had a reference at work, and had to run a cable up the side of the building, for our GPS antenna. The building filtered out radio signals otherwise. And that's a good thing. There was a significant amount of RF inside the building :-)

When your hand-held GPS loses lock, the clock piece inside will free-wheel for ten or fifteen minutes before declaring a problem. I have a GPS that does this (a GPS that used to maintain the time on my WinXP machine).

Paul

[Harry Bloomfield Esq]

I don't remember the DC, but it was when I was young. We then went to

210v AC. AC or DC, the wiring was red and black or near enough, shades of.

Our early TV' and radio were AC/DC and had tapping on droppers, or later, tapping on transformers where AC only.

[Harry Bloomfield Esq]

The AC ones had a pawl and spring mechanism, to force them to start up running the right way. If they started the wrong way, the pawl would begin winding the spring up and eventually force it to go clockwise. A favourite trick of mine, was releasing the spring, so it 50/50 went the wrong way.

A similar motor to a microwave turntable, which can run either way on startup.

[Harry Bloomfield Esq]

That still happens, but not so obviously as the generators come under greater load. They catch up when there is a surplus of generation.

Yep, I remember those with buttons.

[Harry Bloomfield Esq]

There were only 4319999 last night :-)

[Harry Bloomfield Esq]

I enquired of the BBC, back in the analogue days, how accurate their line timebase was. The reply was that it was extremely accurate, and I designed a reference based upon that, tapped from a portable TV, for calibrating my instruments.

[Harry Bloomfield Esq]

You forgot the very technical thump on the side of the case :-)

[Harry Bloomfield Esq]

Or two, maybe three core rubber, but equally bad colouring.

[Harry Bloomfield Esq]

+1

[Ian Jackson]

And for the same power delivery, the peak voltage of DC is 0.707 of that of AC - which eases the required breakdown rating of the cable.

[Harry Bloomfield Esq]

I have a number of times.

[Bob Eager]

Many years ago, I went on an IEE visit to the CEGB control centre. There were two clocks on the big wall. One was synchronous, the other crystal or something.

They were given an absolite difference limit (1.5% I think) over 24 hours. But heads rolled if it reached half that.

[Bob Eager]

Our second turret tuner TV was vastly over engineered (so of course my dad bought it).

It had a set of 'piano keys' above the screen. Press one and a motor rotated the turret to the selected position...