Is Tapatalk working with the new forums? That's good news if it is, the mods were debating whether to add that functionality.
The reason I mention that I believe the modulation they are using is Pulse Amplitude Modulation was based more on a bit of research I've done on PAM, and how they use a fixed "sample" rate (The 20ms rate). Every 20ms they are sending a small pulse. When it hits temp limiting, it only sends an impulse when it needs to in order to maintain temps at the temp limit.
Prior to hitting the temp limit, it is sending an impulse at an amplitude that varies based on the joule setting, and it is sending those impulses every 20ms. You can see as well that during the initial ramp up, the amplitude slowly rises from 0V to whatever voltage it ends up at. At the 20ms sample rate, and varying amplitudes on the way there, when you zoom out and look at the entire fire cycle, rather than looking at individual impulses, you can see that it is attempting to recreate an analog positive wave form.
I'll see if I can find a pic or 2...
In a PAM circuit, there is a train signal always present, the carrier signal... It is at a fixed frequency. Each impulse will be fired on those carrier signals. In our case, they are at 20ms, or a sample rate of 50Hz.
Even in Vlad's scope readouts you can see the carrier signal. In his pics the scope is zoomed way in so you can see the 50Hz sample rate more clearly. Each impulse lasts only 20ms. I have stolen Phil's (shh! Don't tell!) for reference, because it shows the entire firing cycle...
If you look at the beginning of the firing cycle you can see where it is firing one impulse for every sample, and changing the amplitude of every impulse as it ramps up to the joules setting. Once the liquid starts to dry it no longer has to fire to maintain temp, so it only fires as necessary, and only as part of the carrier signal (You can see that in Vlad's pics better).
If it were in Pulse Frequency Modulation, as suggested, that would imply that the frequency is being shifted to achieve the desired wave form. A close inspection of the signal reveals that the frequency never shift from the 50Hz carrier signal, only the amplitude of the impulses. The amplitude of the carrier signal when no impulse is required is extremely low, but ever present.
Hah, sorry if that's way too techno geek. I'm just not seeing PWM, or PFM. Not in their traditional sense. I do see textbook PAM though.