For us neophytes, can you explain first what "
dimmer trimming" is; and then, exactly how the
unit "self-trimmed"?
Is it something like "trimming a wick" (which I understand STEVETERRY, SteveB, and select others used to do) ?
[IIRC, Dilor LitePak dimmers were anything but! The rolling racks resembled the size, shape, and weight of today's
Knaack box, and 12x4kW was a common size, I believe? They were sort of a cream/yellow color?]
The cream with brown lettering 12
channel Litepaks were lighter, smaller and easier to use than what came before. If you ever hooked up an
EDI Scrimmer
portable dimmer, you'll know what I mean. Our initial customer was a lighting rental shop in North Vancouver and our goal was to have a product that was lighter, better and more reliable than his
stock of Scrimmers,
Electro-controls and
Strand equipment.
As I understand it, the word "trimming" did originate with wicks, although in the world of electronic dimmers, it took on a whole new meaning. I started my "career" by repairing the aforementioned gaggle of
Strand,
EDI and EC gear for said rental
house. That these dimmers were electonic and they dimmed lights was their only resemblance to modern dimmers. The control circuits were rudimentary on an epic scale. Trimming was the process of compensating for drift in the control components (thankfully, they had transistors by then) and for any minor changes in the environment - temperature, humidity, phases of the moon,
etc. Each
dimmer had at least two
trim pots. One for the top end of the curve and one for the bottom. They interacted, so you had to set one, set the other then repeat until you had a
dimmer output curve that was as close to useful as you could make it. The chances that the next
dimmer you trimmed would curve-match were minimal. Some dimmers snapped on, some had massive
hysteresis, some drifted while you adjusted them. It was not a pretty sight.
So what was "continuous self-trimming"?
Dimmer curves are all about timing, so if you can conjur up a reliable timing
circuit, you get a reliable
dimmer curve. CST was the application of digital integrated circuits to dimming. I came up with a noise-tolerant zero crossing detector using a Motorola analog IC, hooked it up to a phase-locked-loop using another Motorola CMOS chip, and built a rock-steady 8
bit linear ramp. Each step was 0.7 degrees of conduction regardless of incoming
line frequency (good for gen set operation), and with the newer technology it didn't drift. If it tried to drift, the PLL
circuit self-corrected ("self trimmed"). You could vary the temperature, the
line frequency and the phases of the moon and your entire
dimmer bank would continue to deliver the same curve with all dimmers matched.
While they were self-trimming, they weren't "trim-free". All Litepak dimmers had one
trim pot that set the control
voltage scale to 10v for full on. That was it. Early models had linear-phase curves and no output regulation. Later we added a square-law curve and full regulation.
