Nickel and Mercury Delay Lines on EDSAC

RE: Nickel and Mercury Delay Lines on EDSAC

shabaz — Tue, 31 Mar 2020 21:48:04 GMT

Hi Andrew,

Very interesting blog and video! : ) Amazing how much effort there is to replicate the behaviour of the mercury delay line with the nickel wire - very impressive. As Jon says, glass delay lines were essential in TVs. Interesting how mechanical vibrations ends up being useful for electronics in this way. It also reminds me of filters for radios.. the ultra-high-end ones used mechanical filters : ) I have a radio which contains a few of them.. nowadays it would require a DSP to reach that performance electronically,

RE: Nickel and Mercury Delay Lines on EDSAC

jc2048 — Tue, 31 Mar 2020 20:34:03 GMT

Thanks Andrew, that was an interesting blog to read. I was vaguely aware of the use of delay lines like this, but reading the details is fascinating, as is seeing the version using the nickel wires. If you'd asked me before reading, I wouldn't have predicted that the wave from twisting the nickel wire would propagate any real distance at all.

Sad to say, I didn't know what QI was either: I'm in the UK, but I don't watch television.

For a bit more 'QI', perhaps I could add that, though delay lines like this were quickly superceded in computing, delay lines did pop up later in other areas. There was a mainstream application in Europe, late seventies/early eighties, in television sets for PAL chrominance processing. The line delay was a piece of glass. The delay needed was much shorter (63.943us), but the principle was the same as the mercury line (ultrasonic sound waves propagating through the medium). [In glass, the propagation is about 20 times faster than in mercury.] To get around the temperature variation, they used a special glass where the change to the path length, from expansion, was counterbalanced by a similar change of the propagation velocity. That kept the delay, over a 0-60C range, accurate to within 5nS, which was good enough for the processing.

RE: Nickel and Mercury Delay Lines on EDSAC

DAB — Tue, 31 Mar 2020 17:33:41 GMT

I remember when we had coils of coax hanging all over the lab to get the right pulse delays.

DAB

RE: Nickel and Mercury Delay Lines on EDSAC

ankur608 — Tue, 31 Mar 2020 11:14:02 GMT

Seriously Science...nice article.

-Ankur