It always amazes me when I walk into a “modern” factory and see equipment with control systems from the 1970s. To put this in perspective, Allen-Bradley’s PLC-2 family was released in 1978. It would be another year before you could fax a document or listen to the Village People on your Walkman. General Electric’s Series 6 system would be introduced in 1981, the same year as Microsoft Disk Operating System (MS-DOS) – one year before the Commodore 64. And yet, there are many of these and other antiquated systems still in use today.
最近,我打开我的苹果II,把电话headset in its cradle and dialed into CompuServe. Why did I do this? Because I needed to find information on a programmable logic controller (PLC) first introduced in 1978, and I was hoping that someone on one of CompuServe’s forums could help me. So just what was a PLC capable of in 1978? Not much. The basic PLC handled analog and digital inputs and outputs, and little else. Forget about communications to the outside world, data collection, integrated motion, and many of the modern software and hardware functionality now prevalent on most controller platforms of today.
Considering the prevalence of older technology still in use in manufacturing today, how can you tell when it is truly time to upgrade your control system? After all, what you have now may be working fine. To arrive at a bottom line answer that ensures you are not just buying technology for technology's sake, ask yourself the following questions:
- Are parts readily available from your local distributor?
- Will the programming/diagnostic software run on the most current operating system? If you have to have a 386-based PC with DOS 4.2 in order to run the software, it’s time to upgrade.
- Do you have the people in your organization who can program the software and diagnose issues? If you have to bring someone out of retirement in order to do hex-based math on you’re your current controller, it’s time to upgrade.
- Do you want to collect data or make process information available to other equipment and processes?
- How old is your competitor’s equipment? If your competitor is using state-of-the-art equipment and you aren’t, then they have multiple advantages that you don’t. They are more flexible and efficient. If you are down because you cannot get parts for your old equipment they will take advantage, as they should.
Processor upgrades don’t have to be painful. There are several hardware and software upgrade options within the same manufacturer’s family of processors. Often just the central processing unit (CPU) can be upgraded and input/output (I/O) can remain, as is. Upgrades can be done across several phases—CPU and communications upgrade phase followed by the I/O upgrade phase. A phased approach reduces risk as the updated code can be checked first with the old CPU as a contingency. Once proven, the I/O can then be rewired and tested with the knowledge that the code is complete, reducing commissioning time.
One more question to ask yourself if you're working with outdated technology: Do I really want to rely on spare parts from eBay to keep my plant in production?
BTW…eBay was founded in 1995 – 17 years after the introduction of the PLC-2.
Stephen Blank is chief executive officer ofLoman Control Systems Inc., a certified member of theControl System Integrators Association. He has a bachelor of fine arts degree and is an electrical engineer.
