A diversity of applications and technical changes keep the Programmable Logic Controller ( PLCs ) a viable contender in the control arena.
Jon Giardina
Omron Electronics Inc.
Schaumburg, Ill.
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An Omron CS1 PLC mounted in a cabinet controls machines in a foodprocessing plant.
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Generally, defining a programmable logic controller ( PLCs ) in terms of I/O is the best way to go. A micro programmable logic controller ( PLCs ), for instance, have up to a maximum of 256 I/O. Some have Ethernet connections, good resolution, analog capabilities, high-speed counter inputs, and broad instruction sets.
A nano programmable logic controller ( PLCs ) is application specific with limited options for expansion. Examples include highly defined tasks such as commercial lighting and vending machines. They have a narrow instruction set and small programs, typically only 100 lines or so. At its simplest, it's an inexpensive replacement for relays. You can add on a very limited number of I/O later on. Typically there is no analog capability, no computation ability, and the programming is very basic.
A nano programmable logic controller ( PLCs ) let vending machines be networked back to a center to monitor what needs refilling. This is what designers want: a $100 controller with an Ethernet connection, proving that connectivity is more valuable than other functions.
Programmable Logic Controller ( PLCs ) handles elevator ups and downs
One front on which programmable logic controllers ( PLCs ) are seeing more action is elevator control. Mid-America Elevator of Indianapolis has found a way to address the attrition rate of PC-based OEM elevator-control equipment. Instead of using PCbased equipment, they create an overlay, a type of retrofit, using a programmable logic controller ( PLCs ). Overlay installations run the gamut from two-stop hydraulic elevators to multistoried high-rise elevators. With PC-based control, it can take 10 to 12 weeks for an OEM to wire up the controls for an elevator car. With the programmable logic controller ( PLCs ) overlay, the same job takes about 2 weeks, and costs are about half. "A PC control might have 20 to 25 interface boards that are $2,000 to $5,000 a piece," says Mike Siler, vice president of engineering for Mid-America Elevator. "We can do the same thing with a small programmable logic controller ( PLCs )."
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Programmable Logic Controller ( PLCs ): Motion Controller Information
