Power slider for Coffee-Tech FZ94: Artisan expanded

Slider low for modest heat radiation (illustration by Tije de Jong)

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Slider high for intense heat radiation (illustration by Tije de Jong)

ON or OFF
In the default configuration, each of the three heating elements of the FZ-94 roaster can be switched on and off individually and in many cases this provides a good level of control already.

Gradual effect
Since it takes some time for an element to get up to full radiating power after it is first switched on and since it gradually decreases heat radiation after it is switched off, this enables a cautious and understanding operator to strategically switch elements on and off for a smooth effect on the roast.

For instance, switching off the centre element and increasing air flow 25 seconds before the anticipated temperature surge of First Crack would mostly work to prevent an overshooting Bean Temperature early in the development phase right after FC.

The fiery one in the middle
The heating element in the middle is also more closed in between drum and roaster body and more distant from the left and right air inlets than the other two elements and therefore it gets more visibly red hot, causing noticeable activity of sparks and little flames coming off chaff falling on it through the holes in the perforated drum. So switching it off in time prevents too much spectacle there as well.

Warm up with PID regulating all three heating elements together
Now that we have added an extra PID to control three Solid State Relays switching the three elements, the PID can set the team of three elements to any energy level between 0% and 100% in order to acquire and ksustain a warm-up equilibrium in the machine for pre-heating purposes:

The Fuji PXG-4 PID pre-heating the FZ-94

PID setting on 72% power to pre-heat
In the above graph, you can see how I first set the Fuji to a target value for the high BT probe of 180ºC and at the 8th minute decided to raise this target to 200ºC. I also gradually raised the air flow to 80% of the slider capacity which corresponds to 86% of fan capacity. The lower BT probe in the traditional factory position shows 164ºC then, which corresponds to pre-heating I used to do before the recent modification to the machine. Drum speed 50% of capacity.
The PID eventually settles upon a value of 72% of max power to all three elements.

Could this be done manually?
Since in such cases it can be very convenient to be able to set the power of the elements to something between 0% and 100% and not just full-ON or OFF, I wondered if Artisan could be expanded to allow a manual setting of this element power.

Marko Luther does not have a Fuji PID but he has the PDF of its manual listing all minute optional communication codes and using this often cryptic information he managed to expand Artisan to send the relevant commands to the Fuji, facilitating a very simple slider interface to operate heating power:

Buttons to switch manual slider control of heater power ON / OFF

Creating a slider for heater power. This optional power slider feature is expected to be widely available in a future version of Artisan. Of course, to be able to make use of it, one must have the hardware connected to receive and execute these extra commands.

Power slider in Artisan is installed, here at 90%

One example where this new option came in handy is shown below. Approaching FC, I had apparently kept air flow too low and BT (brown line) overshot the orange target graph by 5 degrees Celsius. You can see how the PID gradually decreases the energy for the heater radiation to compensate for this but we don't want the Rate of Rise to become negative.

PID follow-background after 12minutes, manual power slider at 60% after 15 minutes

Therefore, at 15 minutes into the roast I clicked over to manual power slider mode and first set the power to 55% and then 60% of capacity and as a result the BT could be seen to steadily move towards the planned end time and end temperature of the roast profile.

Improvement
This would not have been possible in the original manual switch FZ-94 configuration since it would take too much time to get the element that was switched OFF before FC to heat up sufficiently to make a difference whereas now it was enough for all three elements to just get a little more hot than they already were.

Result
The course correction took 10-20 seconds and the beans came out in the color that I wanted at the development time (between 3:40-4:00) that I wanted for them. The RoR curve was fairly level towards the end but if did not touch zero and also did not flick upwards again so that's a good thing in my view.

Thanks!
Much thanks go to Marko Luther for once more enabling an innovation.

This optional power slider feature is expected to be widely available in a future version of Artisan. Of course, to be able to make use of it, one must have the hardware connected to receive and execute these extra commands.

PS 15 March 2017

On Facebook, Ram E. Evgi, CEO of Coffee-Tech, added this comment:

This type of control can be ordered from the factory, however, this is not an absolute advantage, as the heaters will start to glow at 70% power and up, anything less than this is baking simple heat with no infra red radiation, so, i'm not sure at all it is any better then on off dived between the 3 heaters, preserving the full amount of radiation at any stage.

Nils Tonning clarified his position:

The intensity and wavelength distribution of the thermal radiation emitted by the heating elements is a function of temperature only. It doesn't matter if they are "glowing".
https://en.wikipedia.org/wiki/Black-body_radiation

My response:

Thanks Ram A. Evgi and Nils Tonning for both your input in the discussion. Whatever the heat transfer medium is in wavelength, I think it may be safe to consider an element in 65% power less active and I will try out a slider spread where zero slider equals 65% and 99% slider equals 99% of power. I think we can agree that most roasting is done in that energy area anyway.