In message 
<CA+u-Crae+cUPJvpZGucn=kt_weay9dvqjdk9okbl9zfs9vn...@mail.gmail.com>, George 
Atkinson 
writes:

>The problem is that most low thermal EMF relays (COTO, Picckering etc) use
>reed contacts for environment reasons, but reeds are not easy to latch.

That's actually not true, Bell labs made latching versions as one of the
first things, because that was the big power-saving in telephony switching.

However, the latching version came with a polarity requirement, you send
current one way to latch and the other to unlatch, and that either meant
having two coils would opposite or significant more complexity in the
relay circuit in the driving registers.  Therefore they went back to the old
"holding coil" model instead.


-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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Never attribute to malice what can adequately be explained by incompetence.
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