Tuesday, March 31, 2009
Thursday, March 26, 2009
PC based Industrial Automation
The concept of using a general purpose Personal Computer (PC) for industrial automation is not very popular in the industry. The control is generally implemented through special purpose computers such as Programmable Logic Controllers (PLC) and Programmable Automation Computers (PAC). In both the cases a Touch panel PC is a must as it has to function as a HMI/SCADA for the operators to interact with. Thus, all these systems consist of controllers as well as PCs.
The article discusses ways to integrate the control functionality to the PC. Thereby reducing the cost of specialized Hardware/Software/Humanware needed to operate the PLC and PACs’.
What is industrial Automation?
Industrial automation is the use of control systems such as computers to control industrial machinery and processes. It makes machines do processes which are boring and repetitive for the humans. Also machines are much faster, accurate, feel no tiredness and needs no overtime. The advantages of automation may show up as higher boiler efficiency in power plants , higher coordination between processes in manufacturing , more comprehensive data regarding plant to help in higher level management decisions in complex control scenarios .At present the Automation of Industries have become a very cheap and easy method to improve quality and lower the costs.
Industrial Automation as of today
Merbok situated at Horana is one of the very few fully automated plants in Sri Lanka
Today industrial automation has become a must for a factory to create products which are competitive in the global market with respect to price as well as quality. In big Automated plants like merbok we get thousands of Inputs and Outputs (IO), thus they have hundreds of controllers networked together to control the plant.
This network of PCs or/and PLCs is called a Controller Area Network (CAN). The CAN is connected with a Supervisory Control And Data Acquisition system (SCADA) and gives the ability to control and monitor the whole plant and improve efficiency and quality of products through reliable and fast interprocess control.
The building blocks of Industrial automation
Automation at the ground level can be implemented using two methods.
1. PC based
2. PLC based
The discussion is mainly focused on PC based automation systems.
The control of the processes is done by the PC. The IO is acquired through the PC using the serial port (RS232/485).
RS232 to RS485 converter module digital Input output module
As RS232 doesn’t support multi point communication, a RS232 to RS485 converter is used to connect with the External IO modules. RS485 is used as the PC needs to communicate with multiple modules. RS485 standard supports up to 256 devices daisy chained together. Instead of a converter we can have a PCI card with RS 485 but it is a much costlier option. The IO modules can be placed near the controlled machinery. Normal IO signal associated with Industrial systems are Thermocouple, RTD, Load cells, Digital, 4-20mA, 0-5Vetc…
The modules are responsible for data acquisition as well as signal conditioning. The data is sent to the Master PC in ASCII format. The communication is completely controlled by the PC as RS485 communication is a Master-Slave configuration.
The data sent to the PC is acquired by the Data Acquisition Program which is running on the PC. It is essentially a Program which reads and writes the data from the Serial Port. This program then gives a method for another program to gain access to data and run the control algorithm. The First software gives the functionality of a Data Center while the second software controls the process with suitable algorithms programmed into the software.
A practical implementation is, Adamview Software as a Datacenter and Visual Basic or C as the control software. Adamview and Labview both have the functionality of datacenter as well as control center. Labview is comprehensive software that can facilitate thousands of IO as well as complex control algorithms whereas Adamview is a simple software where the control functionality is limited. Generally it is only used as a datacenter for Data Logging purposes.
This method has many advantages.
1. No need to get new equipment for the SCADA. The GUI (Human Machine Interface) can be directly programmed in the control software and presented in the PC for the user to interact.
2. The cost incurred is a bare minimum because huge amounts of data can be logged and processed with no extra expense as the PCs (and associated hardware) today are of very low cost.
3. Ability to integrate a Web SCADA such that the supervision and data entry can be done from any place in the world given access to the internet.
4. For inaccessible places wireless communication can be used to relay data.
Given that PC based control being the least cost and easier method for industrial automation, it is imperative that we come up with our own implementation of hardware as well as software, to design a PC based automation solution tailored for our own use, with our own technology to facilitate a cheaper option than the imported (unbelievably) expensive systems.
By Hasala Dharmawardena (stMIEEE)