Re: x10 - CM12U (CM11) Clock Accuracy

["Martin Davies" <martin@xxxxxxxxxxx>]

Jeff & Charles - many thanks for your responses and information. I'm now
beginning to understand the situation a little more!

With reference to your comments ...

>A private generator (not connected to the grid) could certainly be a
>factor.
>One Onan manual for a RV generator says it should run at 63Hz no load,
>dropping to 60Hz under full load.  Even if the generator is only a few Hz
>off, that can accumulate to a clock error exceeding an hour a day.
>However,
>that same error would also show up in any other electric clocks that take
>their reference from the same powerline.

>As I recall from the CM11A beta test, it updated the clock whenever it was
>connected to the PC.  So it would never register a clock error.

>Jeff

When the generator is running the frequency varies between 48-50Hz.  When
not running the load is supported by a full-sine wave invertor stabilised at
50Hz. The timed events are downloaded to the CM12U interface. The PC to
which it is connected is not running the whole time.


>Jeff,
>I believe ActiveHome will only update the CM11A clock on user
>command -or- (automatically and silently) if AC power to the CM11A
>has been interrupted. The OP never stated whether or not he
>unplugged his CM12U from the AC socket when he disconnected from
>the computer.

The CM12U is left plugged into the AC socket all the time - even when the
computer is switched off - with a small number of timed events stored in the
interface.  The CM12U is plugged into an AC socket that is part of an
'essential' supply supported by a battery-invertor system when the generator
is not running, and the generator when it is running. The primary purpose of
the CM12U is to ensure that services that may have been left switched on are
switched off at fixed times to conserve battery power at times when the
generator is not running.


> "posted by Charles"

>The post cited refers to the CP290 (an antique), not the CM11A.
>They're two entirely different beasts, not just in the clock.
>The CP290 used a crystal oscillator which could be improved; the
>CM11A/CM12U uses the AC mains frequency, which you're generally
>stuck with.

>Does your CM12U gain time or lose time?  If it gains time (runs
>fast and timers execute earlier) it's possible that excessive
>noise or spikes on the generated AC waveform could cause it to
>do that, in addition to whatever changes are due to fluctuation
>in the mains frequency.

Ok - understood about the CP290/CM11A; so the clock mod won't apply to the
CM12U?  Is there anyway of 'modding' a CM12U to use an 'internal' clock
rather than using the mains frequency to regulate its timing?

I haven't kept detailed logs of timing errors. Timed events occur both
earlier and later than planned so it is possible that errors may be due both
to the noise spikes and poor frequency regulation.  There is an x10 filter
on the input side to the supply to the 'essential' service.

With thanks,

Martin...