[Info-vax] VMS and the Internet of Things (IoT)

[Chris]

On 09/12/16 18:55, johnwallace4 at yahoo.co.uk wrote:

> The smart meters being rolled out in the UK are required to
> have, as well as the remote metering stuff, a remotely
> controlled power-off switch. No UK law currently permits use
> of this off switch, but that can be changed at a few hours
> notice when the state of emergency arises.

Forgot to mention that, but does raise an interesting
question from an engineering pov. They need to be able to
switch a 60-100 amp load, the usual incoming fuse rating
here in the uk. They can either use an electromechanical
contactor / relay, or a solid state switch. A relay of
that rating is physically bulky, with large silver or silver
alloy contacts That solution would drop insignificant
voltage, but would need to be always on, wasting ~10Va each.
Multiply that by millions of meters = megawatts of wasted
power. While it could be normally closed, ie: contact closed
unenergised, it's doubtful if there would be enough contact
pressure to handle the current rating. If a solid state
relay is used, at that rating, expect to drop 2-3 volts. So,
at a 100 amp load, that relay dissipates 2-300 watts, which
would need a very big heatsink or foced ar cooling to
prevent meltdown and er, who will pay for that wasted power ?.

That's just one of the things that sprung up while reading
the spec. Devil is in the detail, as usual, but the whole
project is completely over the top.

>
> Do people want a Window box in charge of this capability?
> When a Windows (or other) Update disables the USB-serial
> adapter which is likely a critical piece *somewhere* in
> the setup? Or any of the other usual unfortunate stuff
> you get with the usual high volume low value commodity OS
> used in a place where a high volume low value commodity
> OS don't fit right?

Windows might be fine for front end user interface, but one
would hope that any safety or security critical system
would have a fully hardened and avionics grade approved
os of some sort. Doubt it actually happens though :-)...

Chris