PLC Voltage Regulation or Control?

Discussion in 'Embedded Systems and Microcontrollers' started by HighVoltage!, Sep 14, 2015.

  1. HighVoltage!

    Thread Starter Member

    Apr 28, 2014
    95
    0
    I currently want to control the temperature of a metal that is being heated by current induction. However, the correct current must be used in order to achieve a steady temperature (assuming stable conditions). There is a variable transformer (0-480V) that is controlled with a 120V motor to increase/decrease output onto second transformer which steps it down in order to increase current. I have a thermocouple positioned on the surface of the metal in which I am heating. I also converted AC current reading induced onto metal to mVDC (milli-Volts DC). Can I use the mVDC Voltage current signal and voltage reading from thermocouple to control 120V motor using a PLC?

    Your help will much be appreciated!
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,558
    2,378
    1ph induction motor?
    How is the motor controlled now? On/off or variable?
    Using a PLC you would need a analogue input card, and some kind of controller card for the motor, depending on what the technology of the motor is, it may be beneficial to put a P.M. motor of some kind for control, DC or BLDC etc.
    Max.
     
  3. HighVoltage!

    Thread Starter Member

    Apr 28, 2014
    95
    0
    Its a 1 phase synchronous/stepping motor. The motor is controlled with a raise/lower switch. I plan on putting an AUTO/MANUAL switch to have the option should the PLC automation fails.
     
  4. HighVoltage!

    Thread Starter Member

    Apr 28, 2014
    95
    0
    Would I be able to set the desired temperature and the PLC control/keep the current within a certain range without "over-working" motor?
     
  5. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,395
    497
    I assemble machines that use Allen-Bradley PLC. We use standard sensors for input to A-B PLC. What do I mean by standard sensors? The sensors are powered by 24 VDC, the PLC analog voltage input cards receive 24 volts when sensors is On (proxes, rid switches usually).

    So. If you try to use PLC, then research what analog input cards are available for the PLC. Thermocouples output voltages in milli volts, you need "special" arrangement to convert these milli volts into useful data.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,558
    2,378
    What PLC do you intend using?
    Analogue input cards usually store the date in digital fashion and can be read as such by the program.
    I imagine the raise lower switch either uses some kind of stepper output signal or responds to the discrete switch contact?
    If you want feed back control then this is usually some form of PID control in this case the motor is always 'active'.
    Max.
     
  7. HighVoltage!

    Thread Starter Member

    Apr 28, 2014
    95
    0
    The switch works by contact; There is common terminal, one for forward, and reverse (Up/Down) to motor. I tried real hard to see if there was a non-programming way to achieve this. However, I feel as if using a PLC will allow/change parameters I want.
     
  8. HighVoltage!

    Thread Starter Member

    Apr 28, 2014
    95
    0

    What would be an example of a "Special Arrangement" that would help me out if you dont mind me asking?
     
  9. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,395
    497
    From my limited experience two things:
    1. Amplifier to convert thermocouple milli volts into something useable like volts. Then PLC card that would act as ADC to tell PLC the voltage that corresponds to temperature measured by thermocouple.
    2. PLC might have a special card/module that is designed to work with thermocouples (that would make 1 irrelevant). It would basically contain all the parts listed in 1 and have software to understand the thermocouple readings.
     
  10. HighVoltage!

    Thread Starter Member

    Apr 28, 2014
    95
    0
    I see Allen Bradley and others do sell a Thermocouple Analog Input Card! What would I use for the current mVDC signal: An amplifier? This current will need to be set to a certain parameter in order to get temperature. Will the PLC "Hunt" on its own and settle to temperature?
     
  11. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,395
    497
    That makes no sense.
    Current is current.
    Voltage is voltage.

    Thermocouples output voltage, not current.

    The PLC thermocouple input card will do everything for you. All you have to do is read what PLC and the card needs. For example:

    - specific card will work with specific type of thermocouple. So if you have K-type thermocouple, you will need card designed to work with K-type thermocouple.

    - there might be thermocouple length requirement/specification. This may dictate where you place your PLC and other components that are needed to support the PLC.

    - A-B stuff is expansive. My senior design project my team used 2 thermocouples, we connected them to special breakout boards that we purchased (that did three things:
    1. amplified thermocouple voltage
    2. digitized it
    3. sent a digital signal to uC
    ), these board than sent the digital signal that contained temperature value to the uC using SPI hardware/protocol. And, as you probably noticed, my team used uC (Arduino Due board) instead of PLC.

    Why did we use uC? Two reasons:
    1. None of us had done any work with PLC. All of us had class in C language, two of us (the EE) had class in uC. So when it came time to uC, we at least had a clue what we were doing. And we dug up stuff on internetz that other people did with thermocouples and Arduino so we copied the setup that other people used and just modified/wrote software in C that did what we wanted.
    2. PLC is expansive. And by expansive I mean VERY Expansive. The Arduino Due cost us about 25-35 USD, the two thermocouple breakout boards were 10-15 USD each. A-B PLC itself will cost you something like 700-1500 USD (depending on model) and that thermocouple add on card will be 100-300 USD.
     
    HighVoltage! likes this.
  12. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    I suspect that the OP is going to learn more about the stability of feedback control systems than the OP ever wanted to know...
     
    strantor likes this.
  13. HighVoltage!

    Thread Starter Member

    Apr 28, 2014
    95
    0

    Its evident that the cheapest route is to go with Arduino Programming...interesting. However, I am not that familiar with programming in C Language (I guess I can try and figure it out?). I found this link on Ebay for a 20 dollar Arduino...Is this it? Where can I find the special "Breakout Boards"? Do I have to program the thermocouple voltages in the program or will the Arduino recognize? Since I have two DC input signals in mVDC, how will I control the output which is 120VAC (motor)? Will too much current be drawn from controller? Therefore, will a current limiting resistor need to be used?


    LINK: http://www.ebay.com/itm/Arduino-com...solated-I-O-/281211643782?hash=item4179852786
     
    Last edited: Sep 15, 2015
  14. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Lots of breakouts at AdaFruit or SparkFun. I build my own...
     
  15. HighVoltage!

    Thread Starter Member

    Apr 28, 2014
    95
    0
  16. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Breakouts to use with a Uno. I convert the Uno to a Mini to finalize the project, so Breakouts are meaningless to me...
     
  17. HighVoltage!

    Thread Starter Member

    Apr 28, 2014
    95
    0
    Is the program for Arduino available for free or what program is used for programming? Can anyone show me what parts I need so that I can purchase them (model numbers or online links)? I really want to get this project going. I honestly appreciate all the help!
     
  18. OBW0549

    Well-Known Member

    Mar 2, 2015
    1,326
    890
  19. dannyf

    Well-Known Member

    Sep 13, 2015
    1,825
    364
    It requires a PLC with an adc input - pretty much all of them can do that now.

    For a cheaper approach, look to "Ladder logic for pic and avr". It is a simple way to implement and program PLC on pic/avr. I used it to built a controller for a temperature controlled iron handle and it worked out great.
     
  20. HighVoltage!

    Thread Starter Member

    Apr 28, 2014
    95
    0

    What hardware do I need? Your saying you can program a PLC using code instead of ladder logic?
     
    Last edited: Sep 15, 2015
Loading...