I have seen the statement about "the
sine wave on a
dimmer set to 100% being clipped" twice in recent posts and I am intrigued by this.
I have repaired and adjusted many dimmers of different makes and vintage and I have yet to see a
sine wave that is "clipped" on a properly adjusted
dimmer. The word "clipped" means that the peak of the positive and negative half cycles has a
flat top.
Clipping is normally the result of insufficient supply
voltage in a
circuit or the use of
clipping diodes neither of which are normally used in a
TRIAC or
SCR dimmer. I can see this in a true
sine wave dimmer but these are not very common and I have never had the opportunity to repair one so I can't comment.
I routinely adjust dimmers using an oscilloscope which allows me to see the output waveform very clearly - this is much more effective than a true
rms meter or worse using a regular
DMM and trying guess what the error is due to a non
sinusoidal waveform. What you should see on a
dimmer output is an error at the zero crossing points i.e at the 0, 180, 360, 720
etc. degree points of the waveform. This
distortion is a result of the
TRIAc or
SCR forward
voltage drop and response time. This cannot be described as
clipping.
The operation of the
dimmer is that as the turn on of the
TRIAC or SCRs is delayed by the
dimmer setting the
sinusoidal output
voltage remains at zero and then increases at a rate determined by the rise time of the
SCR or
TRIAC to the instantaneous
voltage corresponding to the
phase angle for the
dimmer setting. The output then follows the sinusoid curve until it crosses the 180 degree
point and the
TRIAC/
SCR turns off and the output remains at zero until the turn on
point is reached. This is definitely not
clipping it is called
phase controlled dimming.