- December 05, 2017
- IDEC Corporation
By Don Pham, IDEC
The processing power, data storage and I/O handling capabilities of micro PLCs allow them to be used as the main automation driver for complex machines, processing lines, or even an entire plant or facility.
By Don Pham, Product Manager, IDEC
While a retired automation professional may speak nostalgically of the days when manufacturing was controlled by relays, timers and pneumatics—nobody who has to work with those systems on a daily basis would ever want to go back. In fact, many younger engineers don’t even like working with older PLCs.
Early PLCs had limited I/O capabilities, were cumbersome to program and had minimal ability to communicate. But things have changed. Over the last 20 years and more, there has been constant development among all types of industrial controllers, just as there have been advances with PCs and smartphones. Just a few years ago, there were distinct divisions among PLCs, programmable automation controllers (PACs) and PC-based platforms.
But now, all three product categories have expanded and overlap in many areas. PACs can now support the kinds of sophisticated HMIs and processing formerly only possible with a PC. Processes requiring complex programs and even PID loop control can now be supported with a PLC. In many respects, the PLC to PAC boundary has been erased completely. Let’s take a closer look at how this has happened, and what it means to users today.
Programming and Processing Power
Old PLCs reflect the days when memory and processor capacity were expensive. To maintain reasonable cost and minimum acceptable processing speed, designers limited the size of programs, which therefore limited their complexity. Engineers trying to write code to run a manufacturing line often ran out of space, and the next larger PLC model was liable to be much more expensive. While today’s PLCs still have limits, their capabilities are greatly expanded compared to their precursors, thanks to better processors and far less expensive memory.
Today’s users can run far more complex machines and processes with a relatively small and inexpensive micro PLC. The number of I/O points has grown (Figure 1), as has flexibility. The number of analog I/O slots has also grown, allowing designers to draw from a larger selection of sensors and instruments as they create systems. For example, where an older packaging line might have been able to verify a bottle was in the correct position, now it’s also possible to verify its color via a micro PLC analog or digital communication input.
Figure 1, FC6A PLUS with expansion module in background: This MicroSmart FC6A Plus PLC offers modular, expandable I/O able to grow along with the application.
Production lines needing PID control, such as maintaining product at a specific temperature, typically called for a separate device to control the heater, which was then interfaced to the main controller. PID control, and many other types of advanced analog control, can now be done easily by the main controller for a more seamless operation. The ability to include all the elements of a process from start to finish is part-and-parcel of today’s sophisticated PLCs, even some micro models. It’s never been easier or less expensive to implement highly sophisticated control.
Today’s PLCs have capabilities to interface and communicate using every imaginable protocol. Whereas old platforms were largely limited to serial communication using RS-232 and RS-485, the range now covers the world of industrial networking (Figure 2). Older serial protocols like Modbus are still available, but as networking has become more sophisticated, so has the hardware.
Figure 2, FC6A PLUS closeup: The MicroSmart FC6A Plus PLC can communicate using a variety of serial and Ethernet protocols.
Users today expect to have the same connectivity they get from consumer electronic devices like PCs, and they want it to be just as easy and intuitive. Ethernet in its many flavors is common, both wired and wireless, but a PLC must reach out to other platforms, including iOS and Android to interface with smartphones and tablets for remote access. Sending an operator alarm to the control room is no longer enough in many applications. The PLC now needs to send a text message or email to a technician or manager, or serve up a web page to a browser, wherever those individuals may be, and on whatever web-enabled device they wish to use.
Even configuring and programming a PLC has become simpler. With Bluetooth, a technician doesn’t even need to bring a cable to connect to a laptop. With proper authorization, it’s now possible to stand next to the device and make changes or adjustments without even touching it.
Given the sizes of programs and the amount of data a PLC can now hold, the ability to function as an FTP client or server is a must-have capability. This makes moving large blocks of code or historical information much easier.
All these communication methods “future-proof” the technology so it will be ready as demands become increasingly complex. The ability to reach the Internet and function as part of the IoT or industrial IoT has been extended to all manner of industrial equipment. PLCs now need to be able to support remote access, including the ability to manage access and users, within a framework designed to provide a high degree of cyber security.
As the ability to handle more sophisticated programs has grown, so have the programming options. While older PLC platforms were typically limited to ladder logic, newer offerings can work with ladder logic, function blocks and other popular programming languages. Manufacturers extend convertibility as well by providing mechanisms to recover code written for older platforms and update it to newer systems with the same functionality. For example, IDEC software can take code written for its older FC4A and other systems, and convert it to code which runs in a current PLC.
How Users Benefit
One of the major advances with recent PLC platforms is scalability. They begin with a highly versatile main processor and adjust to the size needed by adding on cartridges/modules for I/O, local HMI (Figure 3) and expanded communication capabilities. Let’s consider a hypothetical example of where such a thing can be used to great advantage.
Figure 3, FC6A PLUS HMI module: The MicroSmart FC6A Plus PLC offers a local HMI option, allowing users to check status and adjust setpoints and other parameters.
Imagine a craft beer brewery (Figure 4). When commercial production begins, it has just a few kettles and tanks, a keg filler and a small bottling line. The brewing process is mostly manual—operators move product from tank to tank by connecting hoses and using portable pumps. The cooking process is also done manually by an operator regulating the heating and adding ingredients.
The bottling line is more complex, but it’s probably second hand or even older. Since it has a lot of moving parts, it may have come from its original manufacturer with a big relay cabinet or maybe a small PLC to control the various functions. It gets the job done with an operator or two keeping a close eye on it, and it doesn’t run all the time anyway.
Figure 4, craft brewery interior: As a facility grows, like this craft brewery, the MicroSmart FC6A Plus PLC can expand as well.
Our brewer enjoys some success: production volumes need to increase and customers are demanding different variations of the original product. Management looks for ways to accommodate the growth without increasing the amount of equipment any more than necessary. Production can be boosted by making setups shorter and product transfer faster. All those hoses and manual changes are replaced by more hard piping and automated valves.
The production process moves into its first stages of automation. Automated valves can be controlled by a micro PLC, and the brew cooker can have PID temperature control. Before long, more micro PLCs get installed, creating the dreaded “islands of automation.” Each process has some degree of automatic control, but nothing is coordinated.
Today’s control platforms help avoid this fragmented approach thanks to their scalability. For example, the IDEC MicroSmart FC6A Plus is a micro PLC, but it can be expanded to control an entire manufacturing operation. Let’s consider how our brewery might expand in a more coordinated and effective fashion.
It still starts out as a manual operation and the bottling line is controlled by a relay cabinet. As an initial step toward automation, the company installs a PLC, and the first program written for it is designed to drive the bottling unit. With the addition of a few basic flow instruments, it becomes possible to get smoother operation from the bottling line and more complete operational data, such as beer volumes, bottle counts, etc.
To get more effective control of the main brew kettle, all the heating and agitation routines can also be handled by the micro PLC. Even though the two operations are independent, the program can be written to control them from a single micro PLC by using different subroutines. With the addition of more I/O modules, it is a simple matter to control the first automated valves and pumps to move product between tanks as it follows the steps from brewing to aging and on to packaging.
As more products are added to the company’s offering, recipe management becomes more complex because more ingredients need to be inventoried and managed. The micro PLC can help here too as it has the capability to store this information.
To handle all these new functions, the program continues to grow along with the number of I/O modules. More HMIs are added in different parts of the plant with the capability to move from screen to screen to control whatever function is needed. With more sophisticated functions, the displays get bigger to make it easier to work with the complex graphics.
The original micro PLC main processor is still there and it has no trouble keeping up because it can handle more than 2,000 I/O points. The entire production, from delivery of raw malt to cases out the door, is now being controlled and monitored by a single micro PLC, and there is still room for growth. Even though the different elements of the process function independently, that one micro PLC can handle them all by making each operation a subroutine in the larger programming framework. It can even provide basic reports to keep management up to date on production and inventories.
Bridging the Gap Between Islands
Perhaps the plant didn’t plan well and created isolated automation systems. The communication capabilities of a modern micro PLC allow it to span the gaps and link together the individual controllers. The ability to use multiple networking protocols becomes critical in such a situation, since one controller may be limited to RS485, while another may use Modbus or some other protocol.
When sub-controllers are interfaced with the master micro PLC, the master can send operational orders down to the slave controllers, and gather performance data from them. This overcomes the problems caused by isolated equipment, and brings everything under one operational umbrella. It also provides the means to support more modern capabilities such as remote access via the Internet.
Should the day come when management decides to move to a larger micro PLC platform within the same family of controllers, the change can be made without the loss of any intellectual property by simply transferring the existing program.
There’s no question the capabilities of even a micro PLC have extended it into a world of new possibilities. The practical applications are limited only by the imagination and creativity of users.Learn More
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