The problem with doing that is that some dimmers provide regulation in order to preserve
tungsten filament life. If the
line voltage is nominal, it may look quite
sinusoidal, with nothing anomalous but a fraction of a volt glitch around the zero crossing. If the
line voltage runs high, the waveform will get chopped to maintain the proper
RMS value. The appearance of the waveform will vary considerably depending on local conditions.
This is true, but only part of the problem--and not one you have to worry about if the
dimmer system has a true non-regulated mode. The other issue is that decent theatrical dimmers usually also have a big inductor (
choke) in series with the load to help reduce
filament noise. This is good for
incandescent dimming, but bad for some electronic
power supplies. It's difficult to predict whether a particular
power supply is going to interact badly with that
choke, so generally testing is required. To do that properly, you should have the ability to mockup a fully loaded
circuit with the fixtures you plan to use, and take a look at the
voltage and
current waveforms on an oscilloscope. That's why
ETC never says, "It's okay to use *generic
fixture* on our dimmers in
non-dim mode." It would be impractical for them to try to test all the possible fixtures from other manufacturers in order to make that claim. They do say that they've tested their fixtures with their dimmers and don't expect any problems (as long as you do actually configure it correctly at the rack, and not just
park it at full in the
console).
@Chris Pflieger Next query; how would you vary the source
voltage: Auto-transformers, preserving the entire original wave form other than the height
? Tapped transformers, still preserving the entire original wave form other than the height
?? Series resistors
??? Series inductors
???? Surely not
SCR's,
TRIAC's,
IGBT's or other solid state devices
????? Please make me an offer.
Toodleoo!
Ron Hebbard
These days, this kind of testing would typically be done using a programmable
power supply capable of synthesizing various voltages, frequencies, and even things like harmonic
distortion and other kinds of interference. They're very cool toys, and
very expensive.
