Today’s new processing and networking power the future looks bright for programmable logic controllers and it’s programming. This has allowed the role of the PLC to expand.
The PLC design has changed significantly. Computer processing power has now added the following to programmable controllers:
- Micro USB slots (Data Storage)
- Ethernet ports
- RS232 / RS422 / RS485 (Serial Ports)
- Several digital I/O bus systems like ASi Bus
System design more than ever is done by asking even more question on what is required when installing a PLC system.
Traditional Questions to Ask:
- Number of input signals? Voltage levels? (Discrete on/off inputs.)
- Number of output signals? Voltage levels? (Discrete on/off outputs.)
- Number of analog input signals? Voltage and/or Current levels?
- Number of analog output signals? Voltage and/or Current levels?
- Operator Interface required? HMI – Human Machine Interface – This is now a touch or function key LCD or LED screen.
Additional Questions to Ask:
- Drives / Motors – What are you connecting to and the communication system required?
- Computer network – Will this join your computer network? What is the connection cable and communication protocol?
- Do you need data collection?
- Do you need data displayed and/or controlled on a remote device such as a tablet or phone?
- Do you need email and/or text messages sent out by the PLC?
There has been a movement to standardize PLC programming. IEC 61131-3
is the standard for PLC programming. It defines three programming methods:
- Ladder Diagram – Graphical structure
- Function Block Diagram – Graphical structure
- Structured Text – Textual structure
- Instruction List – Textual structure
- Sequential Function Chart – Graphical and Textual structure
The above methods to program PLC’s all will do a good job. It depends on how you were originally taught about programming and the experience that your have. Not all PLC’s will be able to program in the 5 different ways. Some will only provide a couple. You will have to see the programming manual of the make and model of the PLC that you want to program.
IEC 61131-3 is good, however this does not mean that every programmable controller will program the same way. It will look familiar between programming ladder in AB vs Siemens vs Omron vs Direct Automation, but the key strokes in the software will be different. Manufactures in my opinion will not come to an agreement to have the software exactly the same for all PLC programming. Why should they take away from their market share?
HMI – Human Machine Interface
Just about every manufacturer’s HMI screen will be programmed with different software. Due to the proprietary nature of communications, I would always use the manufacturers HMI with their PLC. The communications is usually direct to the memory areas, and faster response time.
I believe it is always best to have some computer background information. All of our lives are based upon desktop, laptop, tablets and smart phones. Each of these will have an operating system like Windows, iOS, Android etc.
Higher level languages such as Visual Basic (VB6) will give you the ability to run self contained programs that can install on a computer and communicate to the network. I have used this to retrieve information out of the PLC’s on the production floor and save this information into a database.
The computer languages are not always the easiest to learn, but with the tutorials and information on the web this becomes easier. Once you learn one language well, then this will create a building block of knowledge for you to understand even more.
Microsoft Visual Studio
is a free download and fully functional computer environment. This will include the latest visual basic product.
The ability to share information in the company is important. You cannot find a manufacturing plant without a computer network. This is usually confined to the ‘front office’ and is for email, engineering and accounting. We need to get the information from the plant floor to everyone on the Intranet and/or Internet. This can be done through setting up a web server and using basically HTML and ASP to deliver real time data to the network from the PLC.
W3school has help me to deliver real time data via email and web pages to the computer network.
HTML stands for hyper text markup language and is used for all web pages.
ASP stands for active server pages and is used to communicate from a database to web pages.
We have an abundance of information and ways to learn programming. The language and way will change depending on what you want to do. PLC programming is not just the logic behind discrete input and outputs on a machine, it is the entire system. It is the sharing and use of information for the organization.
I believe that we are going and growing in the right direction with information sharing…
How do you see this change?
Let me know.
If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.
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