Help requested with Mitsubishi FX2N PLC for PID control

Dear all,

I am a student trying to make a project to finish my studies as a Technician in Automation. I have a FX2N PLC which is a chinese semi-clon of a Mitsubishi. It only has digital inputs and outputs and addional module extensions cannot be added. I want to make a PID control to heat up liquid in a little container with a heating element. My idea is to use a external ADC circuit that sends bits in parallel to 4 inputs of my PLC. Those bits will be telling my PLC the temperature registered by my temperature sensor inside the liquid container. As my PLC has transistor outputs I want to use one of those to send PWM to my heating element in order to achive better results than using it as an on/off output.
The PLC's manual from Mitsubishi has over 700 pages but only a very few about PID and for my limited knowledge and understanding those are not really enough
I have a Mitsubishi PID specific manual but it is only for other series, not for the FX.
I will appreciate if you help me with the programming of this PLC to make my project as I cannot find anyone in this area who has any experience with Mitsubishi and the people with experience in Siemens are not willing to have a look at my project.

Many thanks
Best Regards

Marcelo
 
Dear all,

I am a student trying to make a project to finish my studies as a Technician in Automation. I have a FX2N PLC which is a chinese semi-clon of a Mitsubishi. It only has digital inputs and outputs and addional module extensions cannot be added. I want to make a PID control to heat up liquid in a little container with a heating element. My idea is to use a external ADC circuit that sends bits in parallel to 4 inputs of my PLC. Those bits will be telling my PLC the temperature registered by my temperature sensor inside the liquid container. As my PLC has transistor outputs I want to use one of those to send PWM to my heating element in order to achive better results than using it as an on/off output.
The PLC's manual from Mitsubishi has over 700 pages but only a very few about PID and for my limited knowledge and understanding those are not really enough
I have a Mitsubishi PID specific manual but it is only for other series, not for the FX.
I will appreciate if you help me with the programming of this PLC to make my project as I cannot find anyone in this area who has any experience with Mitsubishi and the people with experience in Siemens are not willing to have a look at my project.

Many thanks
Best Regards

Marcelo
Hello

I got some notes from manual which is clearly describing how to programm and tune PID controller with that OEM PLC..
See following quotes from this manual ( maybe you dont look at the right Technical Manual..):
1623945169159.png
 
I'm not sure what you would be learning by implementing a predefined PID block...
The next PLC you come across will have its own block. and the next. Probably OK if you want to stick to one PLC
Might I suggest you implement the PID equation from first principles, also I'm not sure what type of output you have, if it is a relay output, then you probably don't want to be PWM'ing the output, you will blow the output.
The maths in the PID equation is not that difficult ..there are loads of docs around. You might want to look at some microprocessor implementation of PID loops to get the source code, then transpose this to whatever PLC language you want (SCL would be my preference ), this will make sure you are on the right track
http://ww1.microchip.com/downloads/en/AppNotes/00937a.pdf.....for example ..but I have seen much better articles from micrchip

If time is against you ...as it was when I was studying....then go for the predefined block

If you understand how the block works, then you can move easier from one PLC to the next

Good luck with your project....
 
My understanding (and memories) of the FX2N is a Mitsubishi series PLC with fixed I/o CPU with add on modules.

The next point is the Transistor o/p are current restricted to 0.5Amp resistive, less (0.3A) for inductive loads, so you have to be cautious how they are used.
https://uk.rs-online.com/web/p/plcs-programmable-logic-controllers/3209064/

Not sure why ControlsGuy25 pasted pages from the manual - it's easier to provide a link:
http://dl.mitsubishielectric.com/dl/fa/document/manual/plc_fx/jy992d48301/jy992d48301j.pdf .....page 102
The following pages provide you with PID equations.

You will notice there are a plethora of other instructions, so PID isn't regarded as anything special;
It would not be the first time I have taken a closed loop application and used other program instructions to create a PID without using the PID instruction. Why - because you get the result you want instead of a standard PID calculated result.
 
It would not be the first time I have taken a closed loop application and used other program instructions to create a PID without using the PID instruction. Why - because you get the result you want instead of a standard PID calculated result.
Yea I know does it rhyme with wemens
 
Thanks for all the replies. I will not really implement the PID equation from first principles as I am studying to be a technician (3 years), not an engineer (5 years here), and we are supposed to know a lot about techniques but not about advanced maths which I don't really enjoy. Maybe it is easy for you guys to make a PID with that info from the manuals but at least until now it is not easy for me. I am struggling into learning about the data registry which I think is the first step here I need to know how to use.
I intend to use a solid state relay on the PWM transistor driven output connected to my heating element in order to overcome the problem of the low current that this PLC can provide at the outputs.
Are the Q/L/Qna series very diferent to the FX series? (As I have a Mitsubishi PID specific manual but it is only for those series, not for the FX).

Thanks
Regards

Marcelo
 
Thanks for the reply ,,,
Sounds like you have a good idea of the direction you are going to take. There are plenty of videos on youtube that will give you some guidance on how to manage plc memory. Keep at it ...it will click.
The Mitsubishi was the first PLC I ever used...you had to program it with a hand pendant.
 
Thanks for all the replies. I will not really implement the PID equation from first principles as I am studying to be a technician (3 years), not an engineer (5 years here), and we are supposed to know a lot about techniques but not about advanced maths which I don't really enjoy. Maybe it is easy for you guys to make a PID with that info from the manuals but at least until now it is not easy for me. I am struggling into learning about the data registry which I think is the first step here I need to know how to use.
I intend to use a solid state relay on the PWM transistor driven output connected to my heating element in order to overcome the problem of the low current that this PLC can provide at the outputs.
Are the Q/L/Qna series very diferent to the FX series? (As I have a Mitsubishi PID specific manual but it is only for those series, not for the FX).

Thanks
Regards

Marcelo
Hi
I provide se notes from OEM manual.. All is well described... In this document
..
Now you saying that these Maths make you inconfortable..
I cannot go further as.. You need to describe the studied system.. By adding a schematic/sketch/drawing at least..
 
The main problem with be the poor input resolution. Given what you have got I would not even try using a PID. A simple on-off control, like what is used for room temperature control, should be good enough.
 
So that PID manual for the Mitsubishi Q series can be useful for me FX series PLC or not?

The resolution is not a problem, I said 4 bits to take 4 inputs but I can use more bits and more inputs. How many do you suggest as a minimum recommended?
 
What is the temperature range? lets say it is 20 degrees C to 80 degrees C. That is a range of 60 degrees. 6 bits would provide a resolution of about 1 degree. More would be better but I double using more than 8 would help much.
 
The most important lesson you can learn in your project is using the available documentation and working to understand what that documentation is telling you. Getting the exact documentation for the device you're using should be at the top of your "To do" list. You'll find forum questions like 'does this statement from the manual mean this:' will likely get a response because it shows you're making an effort.

If you've got a PLC with only DI/DO, why not do a classic traffic light project or an elevator project that uses discrete I/O only?

What you are doing is like a project from 1964 in the early days of integrated circuits, mimicing an analog input by using multiple DI's. That's a very crude work-around to getting an analog input module. You'll never find anything like it in the real world. It will teach about about the analog noise, intefacing devices (whose A/D has an output compatible with your DI's?) and the logic needed to get an analog value from multiple DI bits.

If you continue on your no-analog-input path, then you'll discover that PID is a decision making function. PID compares the input value to the setpoint value, subtracts the two and any non-zero result is an 'error'. PID then makes a decision as to the polarity and magnitude of output change it should make in order to decrease the error to zero. The tuning terms, gain, reset and rate are used to in making the polarity/magnitude decision.

The PLC's PID function will offer some means of setting values for the tuning terms, a setpoint and the output's 'action' (reverse action for heating).

You'll need to figure out how to get the process variable, the temperature value, into the PID function. I didn't read the documentation screen shots, but a PID function usually offers a PWM function for discrete outputs, for which you'll have to set a 'cycle time'.

So most of the PID is already done for you in the PLC's PID function (assuming PID is available for your version CPU).
 
Hi, I think I need to connect it like this as my ADC provides only 5 volts at the output, however I do not understand that symbol on the base of the transistor on this image extracted from the Mitsubishi hardware manual, it is similar to a resistor, however it has 3 connections instead of 2. Perhaps someone can explain it making a clearer circuit diagram? Thanks

 
"PID manual for the Mitsubishi Q series can be useful for me FX series PLC or not"
I would suggest to relate the two would be totally confusing - PID functions in the Qseries far more involved:
https://dl.mitsubishielectric.com/dl/fa/document/manual/plc/sh080040/sh080040s.pdf

What you are seeing above is a block diagram - showing what you need to know; which is principle of sink / source connections and transistor configuration involved.
You could imagine the resistive device connected to the Transistor base is actually two resistors giving a three point connection at the base. But it's not that either. It is simply a block connected to the Transistor base - what is inside that is a fairly complex electronic circuit with opto-isolators and switching devices to make the o/p Transistor function as designed. Circuit diagrams are available but once you have seen them the block diagram is easier reference.
 
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