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When PLCs were first introduced, they were limited to ladder logic. Communication with other systems via RS232,
RS485 and TCP/IP did not exist and neither did scripts to develop advanced mathematical algorithms for data processing.
So there was a phase where several companies developed custom microprocessor based controllers which allow them to hard code
some of these missing features from the PLC. We at one point had own microprocessor based circuit board for automation
applications. The latest version had a touch LCD,TCP/IP and some other advanced features. This is actually a simple system
to develop, a micro-controller, few transistors, some relays along with other components, and a few hundreds of line of
code and voila; automation the size of a matchbox! Is this the future?
In today’s economics, from a cost stand point, developing a circuit board and related firmware can be expensive and time consuming. Supporting these systems in the field can also be a challenge. But what are the advantage to building a custom controller?
Unless there is a need for advanced and fast running algorithms involving DSP for example or more complex mathematical equations that the current PLCs can’t support, today’s cost of an off the shelf PLC discourages these type of initiatives. Building a custom controller should only be considered for those application requiring specialized functions not supported but PLCs. Or very high processing speed for real time systems.
Custom controller have their place in industry. They are widely used to provide functionality in end user products, small equipment, and play a major rolls in automotive. The vehicle’s network is made of several nodes communicating over CAN or other communication protocol. These nodes are microprocessor based controller with inputs and outputs performing a specific task in a multiplexed system. The real time aspect of these type of application makes it important to have a control system running at the firmware level and not at a higher layer.
Will the PLC ever takeover the customer task specific controllers?
At one point, computers were task specific. We now have personal computers at almost every home performing different tasks. The concept of and OS allow applications to run and access the resources is a very strong concept that allow scalability and versatility. On the other hand, advanced real time controls require full and continuous access to resources. When CPU and peripheral devices achieve a speed level that will allow real time controls to run on top of an OS along with other real time controls, we may start talking about common hardware platforms with scalability at the application level. These cost for these systems will also have to be low enough. We currently have automotive nodes running on a version of Linux using the ARM processors. This is the beginning of a common module that can be used for different nodes and application. In our opinion, this is still a faraway concept that will be feasible at one point or another.
A common controller will be a controller is standard input and output connectors. To replace and engine controller, the user will purchase the controller off the shelf, load the application then install in the vehicle. All controller will be the same but the application will be different depending on the task. For now, it will be difficult for custom controller to take on the PLC world and it will be equally difficult for the PLC to take on the custom controller’s market.