Hi . so, i hav a kiln in my foundry that run on gas. (burn out wax from investment molds)
i have had several controllers on this thing with all sorts of functions, but the one thing thay all fail is to run the kiln like i want.
my requirements is simple. but i have no idea how to do the code.
what it deans to do.....
1 read temperature and start heating to start temp+30 deg C.
hold 10 min. and do that again till it reach 200deg C.
hold 200deg C for several hours, this is one of the 2 aspects that i need do be able to change.
after said holding time do the 30deg C every 10 min till it get to 700 deg C. there it must hold, also for a long time.
would be nice to have a display showing the temp and if possibly the progress, like run time so one can see where you are in the full poses.
i cant use pid because the system run on a on/of flame with a pilot flame. pid confuse the solenoid valve. it can switch no faster than once every few seconds .
hope this make sence
i have arduino uno, nano, promicro, and getting hold of more options is not a problem, but i think nano should be good enough.
max6675 themo breakout
oled i2c thingy
20x4 i2c
to change the soak time (200deg C and 700deg C) can be a pot or button, if i have to change that in the code its not the end of the woeld, most firings are the same, now and then there is a big mold that nead more time....
the output control a mosfet board to control the gas solenoid. the rest is all direct control. pilot and so on does not nead code.
i have looked at doing the code, but its a loooooong learning slope for one simple controller.
if there is any one who can help i would be very greatfull.
in return i can provide info and asistance to any one who want to do metal casting
thank you all
Manus
There are masses of commercially available controllers to do this task . You have to think about packaging , displays , setup switches, power supplies etc .
You could do it with an Arduino product, it’s not too hard a task, - if just question if this is the best route for you - a commercial controller will be cheaper .You need to look at the Gigs and collaborations section of the forum for this .
Hi,
i cant use pid because the system run on a on/of flame with a pilot flame. pid confuse the solenoid valve. it can switch no faster than once every few seconds .
This sounds like the PID was not setup properly, if you needed longer ON/OFF periods then adjustments to the PID parameters can be made. (deadband)
OR
I would also hedge my bet and say your burner could be too big for your kiln.
Can you adjust the energy output of the burner.
How big a kiln is it?
What variation either side of the set temperatures can you tolerate, +/- 1 or 5 or 10DegC when each setpoint is attained?
Where is the temperature sensor located?
Can you tell me how quick from 30DegC to say 200DegC it takes with full on burner.
Can you tell me how quick it goes from 200DegC to 30DegC when the burner is off.
would be nice to have a display showing the temp and if possibly the progress, like run time so one can see where you are in the full poses.
You would like to have a display that shows a chartrecorder type graph.
I assume depending on the load in the kiln, the time taken to reach each 30DegC step will be different.
The time spent at each step and the final temperature are the important parameters?
OR
Is ramp up time a set figure as well?
Tom... 
Since PID cannot work on an on/off device like a solenoid, then you will have overshoot and undershoot.
if you think about the solenoid like a PWM device, but with huge slices of time for each cycle.
then you might be able to tackle the problem by working it as a long duration PWM.
say, your minimum ON cycle for the solenoid is 3 seconds
you could start with 1 ON cycle every 21 seconds and see how warm you get
then run for 2 ON cycles every 21 seconds, log the temperature, then 3,4,5... etc
that would be a simple to create program and data logging is not hard so graphing results would be key to figuring out the best operation.
I would also assume that some kiln groups would have done this so might be a better place to start.
Think about the safety aspect - it would be all too easy for a defect in the code to crash the Arduino leaving the solenoid on. Similarly, electrical issues might do the same thing. I assume a safety cutoff is a standard thing in a kiln - is it?
If you need accuracy at these 30 degree intermediate points, PID is likely to be problematic because of integral windup. Writing something that measures temperature overrun as it goes and compensates for subsequent heating wouldn't be too difficult though.
The PID_v1 library comes with an example called "PWM_RelayOutput". It turns the output on and off only once every five seconds. Perhaps that can be a basis for controlling your burner which "can switch no faster than once every few seconds". It may be necessary to make the period longer and to set a minimum ON interval. For example, change "WindowSize" from 5000 to 10000 (10 seconds) and keep the burner off if the Output of the PID is less than 3000 (3 seconds) or keep it on if it's more than 7000 (7 seconds). That way the changes from ON to OFF or OFF to ON will be at least three seconds apart.
if (Output < 3000)
digitalWrite(RELAY_PIN, LOW);
else
if (Output > 7000)
digitalWrite(RELAY_PIN, HIGH);
else
if (millis() - windowStartTime < Output)
digitalWrite(RELAY_PIN, HIGH);
else
digitalWrite(RELAY_PIN, LOW);
Hi,
I have a different kiln (for 'warm' glass) but I had good results in plotting my temperature over time with Megunolink..
See https://www.megunolink.com/
It also has the ability to create visual control panels on the PC to control arduino systems, but I have not used that...
Worked well for me graphing kiln temperatures...
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