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

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

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

>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..

>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.
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.

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.

HTH ... Marc

Marc_F_Hult
www.ECONtrol.org
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