This project is based on code from pvarney/PiLN
Electricity and heat are dangerous! Evaluate the risk and make go no go decision!
Most kiln manufactures state "Do Not Fire Unattended". Commercial controllers deal with many fault modes that this controller does not address. Intermittent thermocouple connections, stuck relay, shorted element and weak elements, these faults have all happened to me and the control just keeps say "kiln thinks kiln can, kiln thinks kiln can". I had to intervene. Stuck relay and bad thermocouple readings are run away condition that could become meltdown/fire/death. "DO NOT FIRE UNATTENDED!"
Web-based Raspberry Pi Kiln Control:
-
achieved my goal to run on Rasberry Pi Zero W, but I am currently firing on a Raspberry Pi 3b:
- sqlite3 database for firing profiles and logging (small memory footprint)
- lighttpd web server (small memory footprint)
-
kiln sitter(KS) as a sensor
- KS functions as 'ARMED', can not start firing without kilnsitter being armed
- set profile top temp higher than KS cone, KS is intended trigger, thermocouple is safety
Future improvements:
- performance watchdog:
- warning notifications, klexting;
- shutdown when a minimum rate cannot be maintained,
- inductive current sensors: element fault indication;
- crash/loss of power recovery:
- PI comes up, KS is armed & profile is 'Running' then how to consider unfinished segment
- compare temp at the timestamp to current temp
- compare last timestamp of 'Running' firing to current time
- notify on power resume, klexting (kiln text message)
Hardware:
- 20x4 LCD w/ i2c backpack
- $13, (https://www.amazon.com/gp/product/B01GPUMP9C/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1) uses RPLCD library;
- 2 MAX31856 thermocouple module
- $17.50 each, Adafruit (https://www.adafruit.com/product/3263);
- High temperature (2372 F) type K thermocouple
- Thermocouple wire
- I bought the 24awg yellow k-type wire at the pottery store,
- I use about 6 feet, the controller is attached to the wall;
- uln2803a to switch 12V fan and 12V coils of the relays
- $1/each on amazon, using 3 of 8 channels;
- Deltrol 20852-81 relays
- 1 for each segment of kiln, 3 for my kiln
- This is equivalent to relay Skutt uses to switch sections/zones (Skutt model is SPDT, this is same series but DPDT),
- $17.50 each and about that much for shipping (https://www.galco.com/buy/Deltrol-Controls/20852-81);
- 12V power supply
- converts 120vac to 12vdc,
- supplies 12v to relay coils, HDMI monitor, and 5v buck converter,
- $20 (https://www.amazon.com/gp/product/B00DECZ7WC/ref=oh_aui_detailpage_o01_s01?ie=UTF8&psc=1),
- rail mounted;
- 5V buck converter
- converts 12v to 5v USB connector for Pi power,
- $7 (https://www.amazon.com/gp/product/B071FJVRCT/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1);
- monitor w/HDMI input
- optionally can be controlled/viewed from phone or computer on home network;
- terminal blocks to distribute L1, L2, N and GND
- Ground, $6 (https://www.amazon.com/gp/product/B000K2MA9M/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1),
- L1,L2,Neutral, 3 @ $7/each, (https://www.amazon.com/gp/product/B000OTJ89Q/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1);
- #12 awg hi-temp appliance wire to each element;
- 3 ceramic 2 pole terminal blocks
- 1 for each kiln segment;
- crimp terminals, #10 awg, hi-temp appliance
- $.16/each, (https://www.amazon.com/gp/product/B01L2TL63C/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1),
- uses the same crimper used on the elements $16, (https://www.amazon.com/gp/product/B01L2TL63C/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1);
- the crimpers require muscle
- lugs #6 AWG copper
- big crimper
- $25, (https://www.amazon.com/gp/product/B07D7Q54N2/ref=oh_aui_detailpage_o01_s03?ie=UTF8&psc=1),
- I crimp 2 times, first time with correct size, second time reduced one notch(correct size is loose);
- 14 THHN stranded, hardware store, to power 12V supply, white,red,green 2' each;
- hook up wire
- power to pi, fan, relay coils,
- (https://www.amazon.com/gp/product/B07G7W7G4T/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1);
- prototype board to mount everything
- heat shrink, Harbor Freight
Thermocouple tip: One side of the type-K thermocouple and type-k wire is magnetic(red side), Test with magnet to wire correctly.
- Current kiln controller is attached to is a Old Skutt 281, which is a previous model number of KS1027:
- old elements, I am surprised that it easily reaches temp at a reasonable rate, this kiln sat unused, outside under roof for 15 years;
- lid(split and flaking)repaired/coated;
- base(cracks) repaired;
- rust removal on controller boxes, painted;
- built rolling stand out of 2"x3" mild steel rectangular tube;
Stuff to get it to work:
-
Pin-Out:
RPLCD: GPIO 2 SDA RPLCD: GPIO 3 SCL RPLCD: 5V RPLCD: GND MAX31856 Vcc: 3.3V PIN17 MAX31856 GND: GND PIN14 MAX31856 SDO: GPIO 9 MAX31856 SDI: GPIO 10 MAX31856 CS: GPIO 8 & GPIO 7 MAX31856 SCK: GPIO 11 unl2003a 1: GPIO 22 unl2003a 3: GPIO 23 unl2003a 5: GPIO 24 unl2003a 7: GPIO 13 unl2003a 8: GND unl2003a 9: 12V unl2003a 10: FAN black/gnd unl2003a 16: relay #1 coil (input is across the chip on pin1) unl2003a 14: relay #2 coil (input is pin3) unl2003a 12: relay #3 coil (input is pin5) 12V: relay 1,2,3 coils and FAN red/+ -
Install PiLN files in /home and create log directory:
su - pi git clone [email protected]:BlakeCLewis/PiLN.git mkdir ./log ./db ./html ./html/images ./html/style -
Install sqlite3:
sudo apt-get install sqlite3 -
Set up directories/link for web page:
ln -s /home/pi/PiLN/images/hdrback.png /home/pi/html/images/hdrback.png ln -s /home/pi/PiLN/images/piln.png /home/pi/html/images/piln.png ln -s /home/pi/PiLN/style/style.css /home/pi/html/style/style.css -
lighttpd:
sudo apt-get install lighttpd sudo cp lighttpd.conf /etc/lighttpd/ cd /etc/lighttpd/conf-enabled sudo ln -s ../conf-available/10-cgi.conf . sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT sudo iptables save cd chown www-data:www-data PiLN/html/pilnstat.json -
Install required Python packages:
sudo raspi-config #enable interfaces ic2 & spi lsmod | grep spi -
Instal RPLCD for the 20x4 lcd: sudo pip install RPLCD sudo apt install python-smbus
-
Install John Robison's Adafruit Pyhton MAX31856 library:
cd git clone https://github.com/johnrbnsn/Adafruit_Python_MAX31856 cd Adafruit_Python_MAX31856 sudo python setup.py install -
create the sqlite3 database:
sudo chown -R www-data:www-data /home/pi/PiLN/db sqlite3 /home/pi/db/PiLN.sqlite3 sqlite> .read /home/pi/PiLN/docs/PiLN.sql; -
Tuning:
-
Skutt KS1027 with old elements:
Kc: 6.0 Kp: 3.0 Ki: 0.4 Kd: 13.0 Time internal: 30 seconds
-
-
Using the Web App:
On the same network that the RPi is connected, http://<RPi_IPAddress>/pilnapp/home.cgi Or, on the controller RPi, http://localhost/pilnapp/home.cgi -
Start the firing daemon:
python3 /home/pi/PiLN/daemon/pilnfired.py -
PID with C algorithm:
My implementation of a PID algorithm that is optimized for a system that can only add heat; Kc is not determined by a time sensitive value; Ki is not time sensitive; Kp & Kd are determined by an amount of error over a time segment these terms should be normalized by the time segment like (term*60/window) Cterm = Kc/100 * (Current_temp - room_temp); Window = determined by bump test, mine is 30 seconds error = Setpoint - Currrent_temp; Pterm = Kp * 60/Window * error; Iterm = Summation (Ki * error), constrained by (Imin <= Iterm <= Imax); Dterm = Kd * 60/Window * (error - previous_error); output = (Cterm + Pterm + Iterm + Dterm) constrained by (0 <= output <= 100); Window: Size of the base time unit, the controller will decide what to do every window; based on the response time of the kiln (how long it takes to finish reacting to input); my kiln window = 30; bump test turning on kiln for 30 seconds record time/temp every 10 seconds until temp starts falling tau_temp = .75 * (hi_temp - start_temp) window = .25 * (time of tau_temp) Cterm: Kc = 6; steady state term, required amount of energy to maintain temp; linear, inverse proportional to r-value of kiln; my kiln requires about 6% of output per 100C of temp differential; (100C ~= 6% to hold temp, 1000C ~= 60% to hold temp); tune: after determining "window", do a Bisque cone 06 to ~1000C, with a 10 minute hold every 100C; query the database to average output during the holds; mine was about 6% per 100C. Pterm: Kp = 3; proportional to desired change in temp; TODO - test runs with rate 60 and 166 C/hr, query the database and average(pid_output-Pterm) for each 100C segment. Iterm: Ki = 0.4; Imin = -25; Imax = 25; Imax and Imin are hard coded, may need to make tunable or auto-adjusted based on temp and/or temp climb rate; accumlitive error correction of Cterm + Pterm; to reduce "Iterm Windup", limit with (Imin <= Iterm <+ Imax). Dterm: Kd = 13; change in error; Dterm is the acceleration term. it allows time for Iterm to wind up or down, to keep from falling behind or over shooting. output: output = (Cterm + Pterm + Iterm + Dterm); output is a percentage and therefore needs to be constrained by (0 <= output <= 100)
React
Typescript
Django
Laravel
Facebook
Microsoft
Google
Alibaba
D3
Tencent