When we were going to design our PLC, we found choices for hardware design and software architecture. The main issue was, on what criteria should we choose to develop among a variety of possible designs.
Following are the few points that we decided to keep in consideration during the designing of our PLC.
Our PLC should fulfill the current industrial requirements.
Our PLC should be flexible and cheap.
Our PLC should be compact and repairable.
It should follow the most common standards of PLC.
Programming method should be easy and graphical one.
It should provide the enhanced features of PLC.
It should have expandability feature for the future needs.
Modular or Non-Modular
There are two types of PLC’s Modular and Non-Modular. Modular PLC gives more flexibility in adding and removing modules and also provides enhanced features of programming. Therefore we decided to fabricate a modular PLC with five types of prefab modules.
i. PC Module
is. ADC Module
iii. Input Module
iv. Output Module
v. DAC (Optional)
The number of input modules and output modules attached to the PC module (CPU) depend up on the requirements. Our PLC has a module expandability feature up to 32 modules of each input, output and ADC modules.
Due to this feature of multiple modules system, our PLC has become more flexible and powerful.
PC Based PLC
The main module or the Central Processing Unit of a PLC can be designed by using micro controllers and microprocessors based systems.
We decided to use a complete PC and Central Processing Unit of our PLC and named it, as “PC Module” following are the reasons for this choice:
I. PC Processor can support multiple module processing and attachment without sacrifice of processing speed.
II. PC Module provides Processing, Debugging, Programming and Visual Display feature with in a single module. This feature makes our PLC a versatile one in the era of PLC’s.
III. Just changed the processor can increase the number of attachable modules and the processing speed of our PLC.
Cost of PLC
When we go through the prices of available PLC’s we find that the cost of straightforward and cheap PLC range is from at least few hundred US dollars to thousands of US dollars depending upon the types and features provided. We choose to design a PC based PLC to reduce the cost, skill in designing and labor in the fabrication of our PLC. This is why our PLC is cheaper than any other PLC’s available in the market with the same set of features as our PLC.
Method of Programming
There are three standard methods of PLC programming which have been discussed earlier in the previous chapter.
But the programming method used by us is new, unique and a versatile one by providing a user-interface, a large instruction set, and an enhanced capability of programming.
This programming method is named as “PLC Visual Script.” We designed software for VB Script editing, compiling, debugging and printing. This software is powerful and easy to handle. It fulfills all the requirements of PLC programming.
Hardware of our PLC
Our PLC Hardware consist of six types of modules which are given below:
1) PC Module (Main processing unit)
2) Input Module
3) ADC Module
4) Output Module
5) DAC Module (Optional)
6) MAX-232 Serial Interface
The main processing unit module (PC Module) for our PLC is only one but the number of input and output may vary as per requirement up to 32 Module of each one. Physical timer and counter Modules are replaced by the built-in software timers and counters.
Software of our PLC
The software of our PLC consists of many separate programs each program is written for the specific purpose and specific place (Module) depending upon logic.
We can categorize our software into two parts: -
1. CPU (PC Module) related program
2. I/O Module similar program
CPU (PC Module) related programs are given as: -
I. PLC Hardware and Abstraction Layer Program (PLC server)
II. PLC Debugger Program
III. PLC VB Script compiler
I/O Module related programs
I. Input Module Micro controller Programs
II. ADC Module micro controller Programs
III. Output Module Micro controller Programs
In the CPU related program, all the source codes are written in a Visual Basic language. Hardware abstraction layer program enables the CPU to communicate with I/O Module while Debugger program helps and provides the useful information about the changing states of input and output Module according to the terms and condition are given in the Visual Script program. The other part of a program is a low-level programming used for Microcontrollers operations being used as controller units of different input and output Modules.
Following are the few points that we decided to keep in consideration during the designing of our PLC.
Our PLC should fulfill the current industrial requirements.
Our PLC should be flexible and cheap.
Our PLC should be compact and repairable.
It should follow the most common standards of PLC.
Programming method should be easy and graphical one.
It should provide the enhanced features of PLC.
It should have expandability feature for the future needs.
Modular or Non-Modular
There are two types of PLC’s Modular and Non-Modular. Modular PLC gives more flexibility in adding and removing modules and also provides enhanced features of programming. Therefore we decided to fabricate a modular PLC with five types of prefab modules.
i. PC Module
is. ADC Module
iii. Input Module
iv. Output Module
v. DAC (Optional)
The number of input modules and output modules attached to the PC module (CPU) depend up on the requirements. Our PLC has a module expandability feature up to 32 modules of each input, output and ADC modules.
Due to this feature of multiple modules system, our PLC has become more flexible and powerful.
PC Based PLC
The main module or the Central Processing Unit of a PLC can be designed by using micro controllers and microprocessors based systems.
We decided to use a complete PC and Central Processing Unit of our PLC and named it, as “PC Module” following are the reasons for this choice:
I. PC Processor can support multiple module processing and attachment without sacrifice of processing speed.
II. PC Module provides Processing, Debugging, Programming and Visual Display feature with in a single module. This feature makes our PLC a versatile one in the era of PLC’s.
III. Just changed the processor can increase the number of attachable modules and the processing speed of our PLC.
Cost of PLC
When we go through the prices of available PLC’s we find that the cost of straightforward and cheap PLC range is from at least few hundred US dollars to thousands of US dollars depending upon the types and features provided. We choose to design a PC based PLC to reduce the cost, skill in designing and labor in the fabrication of our PLC. This is why our PLC is cheaper than any other PLC’s available in the market with the same set of features as our PLC.
Method of Programming
There are three standard methods of PLC programming which have been discussed earlier in the previous chapter.
But the programming method used by us is new, unique and a versatile one by providing a user-interface, a large instruction set, and an enhanced capability of programming.
This programming method is named as “PLC Visual Script.” We designed software for VB Script editing, compiling, debugging and printing. This software is powerful and easy to handle. It fulfills all the requirements of PLC programming.
Hardware of our PLC
Our PLC Hardware consist of six types of modules which are given below:
1) PC Module (Main processing unit)
2) Input Module
3) ADC Module
4) Output Module
5) DAC Module (Optional)
6) MAX-232 Serial Interface
The main processing unit module (PC Module) for our PLC is only one but the number of input and output may vary as per requirement up to 32 Module of each one. Physical timer and counter Modules are replaced by the built-in software timers and counters.
Software of our PLC
The software of our PLC consists of many separate programs each program is written for the specific purpose and specific place (Module) depending upon logic.
We can categorize our software into two parts: -
1. CPU (PC Module) related program
2. I/O Module similar program
CPU (PC Module) related programs are given as: -
I. PLC Hardware and Abstraction Layer Program (PLC server)
II. PLC Debugger Program
III. PLC VB Script compiler
I/O Module related programs
I. Input Module Micro controller Programs
II. ADC Module micro controller Programs
III. Output Module Micro controller Programs
In the CPU related program, all the source codes are written in a Visual Basic language. Hardware abstraction layer program enables the CPU to communicate with I/O Module while Debugger program helps and provides the useful information about the changing states of input and output Module according to the terms and condition are given in the Visual Script program. The other part of a program is a low-level programming used for Microcontrollers operations being used as controller units of different input and output Modules.
