Re: Making an X-10 lamp module immune to dimming

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Marc_F_Hult" <MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:18al449g45ucap3mkq61128pqvn6skm7tc@xxxxxxxxxx
> On Sat, 7 Jun 2008 06:46:48 -0400, "Robert Green"
> <ROBERT_GREEN1963@xxxxxxxxx> wrote in message
> <rYadnVE6-IgY-tfVnZ2dnUVZ_rbinZ2d@xxxxxxx>:
>
> >Would another way to say that be the light level is determined by the
> >point on the sine wave where the gate pulse arrives and that that unit
> >stays on until the
> >end of the cycle, no matter what happens afterward in that cycle?
>            ^^^^^                                           ^^^^^
>          half-cycle                                      half-cycle

My bad again.  Should have said "Stays on until the zero crossing is
reached."

> >So it's not possible to have a sine wave that has four "bands" of on/off
> >pulses?
>
> Right. Only one per zero-crossing = two per complete cycle = one per
> half-cycle..

One chop per "hump" - I can remember that.  It sounded so plausible that a
lot of little chops were possible, especially when Isaac reported that there
were additional (although unused) pulses on the gate line beyond the
triggering pulse.  It also sounds like the triac process is something of an
avalanche-like process:  easy to start with very little energy required but
hard to stop when large amounts of energy begin to flow.

I used to think triacs and thyristors worked the same way, but I recall that
my Vivitar 283 fossil flash is able to meter out very short pulses from a
large capacitor by using a photoreceptor of some sort that can measure and
react to flash intensity.  I'll see what Google has to say . . .

> >Or is it just that way for the X-10 modules?
>
> This is true for all TRIAC-based dimming of AC.

> >I thought, when you talked about pulses, that each one of them turned on
> >the triac for a tiny bit of time, and that all of them added together in
> >each cycle increased the power output.  That would require switch the
> >triac on and off multiple timeswithin the cycle.  That description is
> >true of how all the chopped A/C cycles add up, but I think you're saying
> >the pulses that follow are not having any effect on the state of the
> >triac.
>
> Right. Dimming by TRIACs is called "phase-control" dimming for a reason.

Makes sense to me!

> One can characterize the amount of dimming by stating the number of
> degrees after zero crossing ("phase") that the TRIAC goes into conduction.
> The relationship between phase and light output is very non-linear and is
> called the dimmer curve. Turning the TRIAC on as late as 20 degrees (out
> of 180 degrees peer half cycle)  still results in nearly 100% light
> output, but less than 10% of fully on if delayed to 110 degrees.

Is that mostly an "area under the curve" sort of issue?

> I have constructed a spreadsheet of conduction ("phase") angle, turn-on
> delay, resulting light intensity for typical incandescent lamp, RMS
> voltage, and DMX-512 and 0-10vdc control signals that can be downloaded at
>
> www.ECOntrol.org/dimmers/TRIACDimmerCalcs_MFHult.pdf
>
> It also provides the relevant equations and graphs of conduction angle vs
> light intensity and conduction angle vs RMS voltage.

I'll take a look.  Thanks!

--
Bobby G.