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Thread: How I wired a PID to control temperature

  1. #1
    Boolit Buddy Shotgun Luckey's Avatar
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    How I wired a PID to control temperature

    This is how I wired my temperature controller:

    Items purchased from http://auberins.com/

    Universal 1/16 DIN PID Temperature Controller http://auberins.com/index.php?main_p...products_id=90
    25 amp SSR (solid state relay) http://auberins.com/index.php?main_p...&products_id=9
    Heat sink for SSR (will help maximize the life of the SSR) http://auberins.com/index.php?main_p...products_id=45
    K type thermocouple high temperature http://auberins.com/index.php?main_p...products_id=22

    Item purchased or supplied locally:

    Crimp on wire connectors, spade type
    Short heavy duty extension cord – my Lee pot has a 2 conductor plug and is not grounded, so the my wiring does not include a ground as nothing in the wiring needs it.
    Small amount of extra wire for jumpers
    Terminal wiring block. Mine has 2 rows of 4 screws. Available in the automotive section.

    Procedure:
    1) Mount terminal block to base
    2) Cut extension cord in half. Strip wires and crimp in spade terminals.
    3) Attach 2 modified cords to one side of terminal block in order from left to right---
    a. Outlet black | outlet white | plug white | plug black
    b. This is the inlet/outlet side of the terminal block, the other row is all for internal connections. The Outlet refers to the end of the cord you will plug the casting pot into.
    4) Mount SSR to heat sink and mount this assembly to the base. Don't forget to put a dab of the white heatsink grease on the back of the SSR before you attach it.
    5) Wire T1 of SSR to screw terminal across from Black Plug Wire
    6) Wire L1 of SSR to screw terminal across from Black Outlet wire
    7) Install a short jumper wire from screw terminal across from White Outlet Wire to screw terminal across from White plug Wire
    8) Mount PID controller to base
    9) Run a pair of wires from screws across from White Plug Wire and the Black Plug Wire to PID AC/DC input contacts 1 and 2 on my controller, polarity does NOT matter with AC power
    10) Run a wire from PID SSR+ (contact #6) to SSR A1+
    11) Run a wire from PID SSR- (contact #7) to SSR A2-
    12) Connect the thermocouple to PID TC (contacts 9 and 10)

    I wanted to add some pictures but haven't figured out how to do that.
    Shotgun Luckey
    SASS #42629
    I'm not a top Cowboy Action Shooter, so I HAVE to look good doing it.



  2. #2
    Boolit Master

    Pepe Ray's Avatar
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    Hi Shot Gun Lucky'
    Great post! I think!
    Perhaps your the dude that can help me out. My electrical background is dated. 1960's thru 1980's. I can wire my home and workshop but my vocabulary ends when switches became relays. I learned about thermocouples when working on gas water heaters. What the 'H' is a PID?
    OK here's my problem.
    When the mill, my employment, shut down, I scrounged some stuff from the casting shop. Legally!! I got a commercial 220V Pot (200 lbs or more). Connected to it was the thermocouple and the thermostat (110V). They wouldn't let me have the switch (inter phase? 110 signal to 220 load?). All of my resources showed new switches in the $200+ range. So I installed a manual switch (220) , and a set of idiot lights to tell me when to throw the switch, either ON or OFF.
    This has worked for me for 8 yrs but it does require that I divide my attention between watching the lights and pouring the stream.
    For a few years now I've been reading the threads discussing the electronics used in melting lead and I'm guessing (hoping) that a cheaper switch/relay is now available. But my familiarity with the language, or lack of, is hampering my ability to search for it.
    Would it be too much to ask for some guidance?
    TIA, Pepe Ray
    The way is ONLY through HIM.

  3. #3
    Boolit Master at Heaven's Range jawjaboy's Avatar
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    PID? With temperatue being the variable, the PID controller is a thermostat with a lil bit/lot of sense. Tuneable.

    http://en.wikipedia.org/wiki/PID_controller


    .

  4. #4
    Cast Boolits Owner



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    Great post Luckey! Is there any chance you can post pictures?

    R.
    "Things always get better once thought, time, and money are applied in the correct amounts at the correct time"
    - No_1 -

    "The only way to deal with an unfree world is to become so absolutely free that your very existence is an act of rebellion."
    - Albert Camus -

  5. #5
    Boolit Master on Heavens Range
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    If you use a "modern", cheap, self-programming/auto-tuning, model, don't let it operate in programming mode until the pot is up to temp. This would be when the pot is fully melted and fluxed, and ready to go. Then turn on the self-programming mode to narrow down the temp range. You should have a seek temp from a notebook for each mold and lead composition. If not, set the temp manually until boolits are correct, and then mark in the book for next time. ... felix
    felix

  6. #6
    Boolit Buddy Shotgun Luckey's Avatar
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    let me preface this with a disclaimer,
    I am not an electrician and I did not stay at a Holiday Inn Express last night
    but I will try my best to answer the questions

    Quote Originally Posted by Pepe Ray View Post
    I learned about thermocouples when working on gas water heaters. What the 'H' is a PID?
    a PID is basically a computerized thermostat

    Quote Originally Posted by Pepe Ray View Post
    OK here's my problem.
    When the mill, my employment, shut down, I scrounged some stuff from the casting shop. Legally!! I got a commercial 220V Pot (200 lbs or more). Connected to it was the thermocouple and the thermostat (110V). They wouldn't let me have the switch (inter phase? 110 signal to 220 load?). All of my resources showed new switches in the $200+ range. So I installed a manual switch (220) , and a set of idiot lights to tell me when to throw the switch, either ON or OFF.
    This has worked for me for 8 yrs but it does require that I divide my attention between watching the lights and pouring the stream.
    For a few years now I've been reading the threads discussing the electronics used in melting lead and I'm guessing (hoping) that a cheaper switch/relay is now available. But my familiarity with the language, or lack of, is hampering my ability to search for it.
    Would it be too much to ask for some guidance?
    TIA, Pepe Ray
    Does your thermostat have electrical contacts to control the switch? If it does have contacts, does it provide power to energize a relay or lamp? (this can be tested by hooking up a voltmeter to the contacts or a small light bulb)? or does it just provide a switch to turn power off and on?

    If in fact it does provide DC power, you can use this signal to power a SSR (an SSR is a Solid State Relay, in other words it is a switch that uses a low voltage, low current signal to turn off and on a "SWITCH" for the high voltage, high current load)
    If the thermostat "output" is switch, it would be a little more invoved to wire, but It could be done.
    The SSR that I referenced and purchased is rated for up to 400 volts and 25 amps. they also carry SSR's rated for upto 100 amps. The 25 amp model is going for $15 and the 100 amp model $40.

    All the parts I purchased came to just under $100...All this to control the temp on a $55 casting pot...LOL
    Shotgun Luckey
    SASS #42629
    I'm not a top Cowboy Action Shooter, so I HAVE to look good doing it.



  7. #7
    Boolit Buddy Shotgun Luckey's Avatar
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    Quote Originally Posted by no_1 View Post
    Great post Luckey! Is there any chance you can post pictures?

    R.
    I would love to but I haven't figured out how to do that yet!!!
    Shotgun Luckey
    SASS #42629
    I'm not a top Cowboy Action Shooter, so I HAVE to look good doing it.



  8. #8
    Boolit Master

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    OK Shotgun Lucky;
    Well, in spite of not picking up on some of the details of my set up, You've targeted my problem. Neat!!
    My thermostat was originally (at the mill) using 110V to signal/trip the $200 plus switch to relay the 220V to the pot. Tho, I'm sure, it could do it with D.C. I see no need to purchase a DC source for this.
    I guess what I need to know now is==Is an SSR ONLY for DC in,AC out? Or can they do 110AC in, 220VAC out? Where do I find an affordable SSR? OR do I go back to my idiot lights?
    Well, it's been interesting. Thanks a bunch.
    Pepe Ray
    The way is ONLY through HIM.

  9. #9
    Boolit Master uncle joe's Avatar
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    shotgun
    try this site we buy stuff from them all the time good prices and sounds like you may need a heavy duty relay to control the element. Be sure you check how many amps it pulls and get a relay a little over rated to handle it.
    http://web5.automationdirect.com/adc...ds/9_to_25_Amp

    ps pid stands for proportinal intergral derivative basically it adjusts the output based on how far off the actual or measured temp is off from the set point. It will learn the temp ups and downs and start trying to compensate for differences quicker. I would suggest you run it for some time then while running push the auto tune button and it will use all the past data it has saved to calculate new settings for dead bands and such.
    please post pics when you can and good luck
    Μολὼν λαβέ

  10. #10
    Boolit Buddy Shotgun Luckey's Avatar
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    here is the wiring diagram, I need to use my son's camera to take some pics of the project, my phoe just doesn't cut it
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	pid low res _320x240.jpg 
Views:	5204 
Size:	33.4 KB 
ID:	8509  
    Shotgun Luckey
    SASS #42629
    I'm not a top Cowboy Action Shooter, so I HAVE to look good doing it.



  11. #11
    Boolit Master on Heavens Range
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    Let's see if I can help with the understanding of a PID controller a little bit. It helps keep me abreast of my technical writing skills.

    There are three logic sections involved in the computer part. The first section, is what is called the proportional section (P). Think of it as a dumb person who can raise the temp of the pot and lower the temp manually like all of us do now. When the temp is too low, we raise it; and, vice versa. It is AFTER the fact, right? That does not take much thought. So, what if we got smarter and stuck a measuring device in the pot. Then we can raise and lower the temp BEFORE the fact occurred, the fact being either a too high or too low temp. This is what is called the Integration Section (I), because we are applying info we gathered over time. After doing this for a while we find that we are getting the temp too hot too quick, or too low too quick, called "ringing" in the literature, and is indicative that we are out of sync way too much. What we need is something to get us in sync, and that would be the third section, called the Differential section (D). If we knew how fast the lead is to get up too exactly right, we can turn the knob much more appropriately each time we turned it. We have just added the info we know about the material we are bringing up, or down, to temp.

    The computer works with DC current and the pot works on AC current, and lots of it. To bridge the two things together we need the SSR.

    ... felix
    felix

  12. #12
    Boolit Buddy
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    Post

    Quote Originally Posted by felix View Post
    Let's see if I can help with the understanding of a PID controller a little bit. It helps keep me abreast of my technical writing skills.

    There are three logic sections involved in the computer part. The first section, is what is called the proportional section (P). Think of it as a dumb person who can raise the temp of the pot and lower the temp manually like all of us do now. When the temp is too low, we raise it; and, vice versa. It is AFTER the fact, right? That does not take much thought. So, what if we got smarter and stuck a measuring device in the pot. Then we can raise and lower the temp BEFORE the fact occurred, the fact being either a too high or too low temp. This is what is called the Integration Section (I), because we are applying info we gathered over time. After doing this for a while we find that we are getting the temp too hot too quick, or too low too quick, called "ringing" in the literature, and is indicative that we are out of sync way too much. What we need is something to get us in sync, and that would be the third section, called the Differential section (D). If we knew how fast the lead is to get up too exactly right, we can turn the knob much more appropriately each time we turned it. We have just added the info we know about the material we are bringing up, or down, to temp.

    The computer works with DC current and the pot works on AC current, and lots of it. To bridge the two things together we need the SSR.

    ... felix
    Not quite.
    The proportional section is the setting it takes to maintain the temperature when nothing is changing, also called the "steady state" setting. This is the same setting as you turning the rheostat temp control on a manual pot to 5 for 500 degrees or 7 for 700 degrees (to make a simple example). Can take a long time to get to full temp as you aren't trying to use any extra energy to GET the metal hot, just the energy needed to KEEP the metal hot.
    The integral section is correct, how far away is the current temperature from the desired temperature and use the information to overcompensate. At the extreme it is turn the pot rheostat control to max when the metal is below temperature, turn it off when the metal is at or above temperature. Deliberately tends to cause the metal temperature to swing from too cold to too hot and back to too cold as this part's purpose is to get a quick reaction to the metal not being at the correct temperature.
    Differential is close to right - how fast is the pot changing temp and use this info to moderate the integral section. If the temp is going up fast, turn down the heat setting, if the temp is falling fast, turn up the heat setting.
    When the pot is at the correct temperature, the integral and differential additions should be zero and the pot shouldn't change temperature.
    Until you come along and pour some bullets and now not as much heat is needed to maintain temperature so the temperature of the metal starts to go up and the integral and differential both turn down the heat, then the pot starts to cool to temp and the integral keeps the heat turned down while the differential starts turning the heat up. Then you add more metal and cool things off and the integral and differential both turn up the heat until the pot starts heating up, then the differential starts turning the heat down while the integral keeps the heat turned up until the pot reaches the proper temperature again.
    The integral and differential working against each other keeps the pot temperature from oscillating, too hot to too cold and back to too hot; while still reacting quickly to the changes in the temperature of the metal; trying to keep the temperature constant.
    Last edited by Firebird; 08-24-2008 at 02:26 PM. Reason: Spelling and clarity

  13. #13
    Boolit Master on Heavens Range
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    Very good! ... felix
    felix

  14. #14
    Boolit Master August's Avatar
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    What a great thread!!!

    How is the "learning" affected by (1) the diminishing amount of lead in the pot as it is used up, and (2) the initial 'start-up' of melting ingots?

    Or, perhaps a better question is: How small a pot would this arrangement be practical for?

    Again, thanks to you guys for sharing this information.

  15. #15
    Boolit Buddy
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    I haven't had to write a learning PID controller, mine were all tailored for a specific product where I could do testing and lock-down the coefficients for the equations etc. But I know what I would do to write the control software and where the problems would be found.

    Initial start up would tend to make the integral part be more important as you are limited to how much heating power the pot has, so during initial melting the power would get turned up all the way and left there for 15-20, maybe 25 minutes while the metal melts. Then later as you cast the integral is made less important as the pot of metal is at temperature and the temperature isn't changing much. This isn't very hard to accomplish as during the initial heating you have a large difference between the desired temperature of the metal and the actual temperature, so you have a naturally large integral section contribution. And as the temperature difference gets less then the integral section naturally gets less. SInce the action of the pot and the action of the software are "in sync", you really don't need to change the coefficients of your PID equations to keep things balanced.

    The diminishing amount of metal as you use it up changes the proportional section, gradually lowering it as the amount of metal gets less and less. This is easy for the controller to do as it is a very slow process as far as the controller is concerned. A sampling rate of 100 times a second is easily done, so something that takes many minutes is VERY, VERY slow to the controller.

    How well will a PID controller work for a small pot - it's not the size of the pot as much as the RELATIVE power of the heating element. A small pot with a small heating element is going to work exactly the same as a large pot with a proportionally large heating element. What could cause problems is a small pot with a very large, heavy heating element that by itself contains a lot of energy (an "over-powered pot if you will) as you need a very sensitive differential section to control these situations. The problem is that by the time the metal in the pot starts to heat up, the over-sized heating element has so much extra energy already in it that you will overshoot the desired temperature even if the power to the element gets turned off completely once the metal starts to increase it's temperature. i.e. by the time the metal in the pot moves from 695 to the desired 700 degrees, the heating element goes from 695 to 900 degrees. All that heat in the heating element is going to raise the temp in the pot no matter what the controller does; so the controller has to make sure the heating element never gets to 900 degrees in this situation. The controller has to learn to shut down the heating element even if the temperature of the metal hasn't changed very much; this means the differential section would have to be very small for falling temperatures (as the integral section would provide the heating needed), and very large for raising temperatures so that the heating element would get shut down very early. This would be the most difficult part for the controller to be able to learn.

  16. #16
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    This thread should be made a Sticky, great stuff here!

    The knowledge on this site continues to amaze me!
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  17. #17
    Boolit Buddy oldtoolsniper's Avatar
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    I just built one and started using it today on a small lee pot. I like the fact that you guys whom understand these things are breaking it down to my potato head level. I have no understanding of electronics because there are no gears or levers that move, it just blinks and works or it doesn't.

    That being said it is simple to build it took about an hour and I checked and rechecked everything about 8 times. I plugged it in and no smoke! It works!
    “Work hard! Millions on welfare depend on it!”

  18. #18
    Boolit Buddy oldtoolsniper's Avatar
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    So how does the self learning mode get effected if I change the temperature for different molds and alloys?
    “Work hard! Millions on welfare depend on it!”

  19. #19
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    It doesn;t. as far as I know. The pot will still react the same way I.E. Heat up and cool down at a linear rate.

  20. #20
    Boolit Master
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    In that no ones has asked this before it's probably a dumb question, but. Are you folks just sticking the thermocouple in the top of the pot or building a holder of some sort to keep it off the bottom and away from the sides? Or does it go somewhere else?
    Thanks, electronically challenged, Steve.
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