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Homeroasters - Home Roasting Coffee Community » DATALOGGERS - CONTROLLERS - RATE OF RISE METERS » Dataloggers/Controllers/Rate of Rise Meters

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TC4 compatible controller
FreshCoffeeDK	#1 Posted on 05/18/2020 6:10 AM
Newbie Posts: 7 Joined: March 11, 2020	Hi there, I'm just in progress of building a TC4 compatible controller that combines the LCD display, buttons, LEDs, temperature inputs and 2 potties for manual control. It should be used for a fluid bed roaster I'm just building. There is also a separate PCB for the high voltage part, that contains the zero-crossing detection and a SSR (triac) control for the fan. I'm wondering if I could use a big contact to control the heat element (3 phase, 7.5kW). I'm very new to TC4 and Artisan but how "slow" I can make the PWM for the heat element? Could the PWM period be in the seconds range? Thanks Stefan FreshCoffeeDK attached the following images:


renatoa	#2 Posted on 05/18/2020 6:46 AM
Administrator Posts: 2588 Joined: September 30, 2016	The slow pwm period influence the control precision. For 50 Hz mains and 1% precision you need 0.5Hz cycle, i.e. 2 seconds on-off period. Shorter period will degrade precision, and yes, you need that 1%, a power step of such magnitude will equate to 3-4 C degrees ET change. Longer period will bring better precision, but control lag. If you have ZCD I recommend to use ICC instead slow PWM, the precision will be given by mains frequency, i.e. 1% for 50 Hz, or 0.8% for 60 Hz, not related by cycle length, ICC is a power control method with instant response. ICC is also preferable to PWM or PAC because no transients are generated, so no interference with household appliances. Regarding to pot control and precision, is not easy to nail 1% using a potentiometer, unless you are using a multiturn model. For this reason, for my TC4 clone approach I switched to incremental up/down push buttons instead pots.


FreshCoffeeDK	#3 Posted on 05/18/2020 8:52 AM
Newbie Posts: 7 Joined: March 11, 2020	Thanks for your reply, what stands ICC for? Never heard of that.


JackH	#4 Posted on 05/18/2020 9:18 AM
Administrator Posts: 1809 Joined: May 10, 2011	The only definition I see for ICC is the International Conference on Communications, which is an organization and not a process. I was not aware that PWM was "slow". Do we need 1% precision in coffee roasting? ---Jack KKTO Roaster.


renatoa	#5 Posted on 05/18/2020 10:29 AM
Administrator Posts: 2588 Joined: September 30, 2016	ICC stands for Integral Cycle Control, you can find this acronym in TC4 sources. It can be found in user.h too, which is a file that is highly recommended, if not mandatory, to review before loading TC4 on your board. For example: Code Download source #define PHASE_ANGLE_CONTROL // phase angle control for OT2(fan) and ICC control for OT1(heater) In professional and academic power control technical documentation it is rather found as PSM (pulse skip modulation). ICC seems to be a particular notation used mainly in TC4 ecosystem. A technical explanation of this control method can be found in this article: https://www.elect...pin/38326/ Regarding PWM speed, in TC4 we have Fast PWM designation for PWM on IO3 output, where modulation frequency is in the kHz ballpark, much bigger than 50/60 Hz of the mains, and Slow PWM, on OT1, for heater controls, where 1 Hz cycle is the default, in the same ballpark with usual heaters thermal inertia. Quoting again from user.h: Code Download source #define CONFIG_PWM // slow PWM on OT1 (heater); fast PWM output (3.922kHz) on IO3 (DC fan); ZCD not required Do we need 1% precision? As I wrote, 1% in power variation equates to 3-4 C degrees variation of hot air. This could mean a lot for those who roast watching carefully RoR evolution, and nothing for those who roast mainly on a constant power level from charge to drop... both of them could have great results in the cup at the end of the day. Depends where you find fun in coffee roasting, in the cup, or in the tinkering :D


greencardigan	#6 Posted on 05/19/2020 8:06 PM
1 1/2 Pounder Posts: 1178 Joined: November 21, 2010	Quote FreshCoffeeDK wrote: I'm just in progress of building a TC4 compatible controller that combines the LCD display, buttons, LEDs, temperature inputs and 2 potties for manual control. It should be used for a fluid bed roaster I'm just building. There is also a separate PCB for the high voltage part, that contains the zero-crossing detection and a SSR (triac) control for the fan. I like this idea. What Arduino are you using? It's hard to say how slow you can go with the heater PWM. It depends how much your output air temperature fluctuates over each cycle. I've never done any measurements but was using 1Hz on a popper a long time ago without any noticeable issues. However, I'm currently using the Integral Cycle Control / Pulse Skip Modulation as Renatoa recommended. Using 50Hz AC you should be able to get 1% resolution. 50Hz mains crosses 0 Volts twice per cycle or 100 times per second.

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