Regardless of the industry you are in, the universal workhorses for automating a piece of equipment or process are simple hardwired controls like cube relays, timers and counters.
You can find these devices in discrete and process industries, on
the plant floor in the manufacturing environment and even in commercial
and consumer applications such as gate controls, vending machines and
amusement equipment.
They work just fine, doing their assigned
tasks as required so what’s the problem? At least, that’s the question
many OEMs are asking as they try to justify continuing to use these
legacy control designs to meet evolving business objectives.
“These small controls are everywhere,” says Paul Ruland, spokesperson for Siemens Energy & Automation. “And this poses a quandary for end users faced with changing needs or the risk of obsolescence.
At
the end of the day the answer to that critical question is simple and
highly significant considering the current state of the economy, adds
Ruland. They cost more than the alternatives. They cost more to
install, to run and to support.
The best alternative, according to a white paper by ARC analysts Himanshu Shah and Craig Resnick titled Five Things to Think About Before Using Hardwired Controls Again, is the programmable relay.
Programmable relays are microprocessor-based controllers with similar capabilities to Programmable Logic Controllers (PLC)
with built-in timers, counters and compare instructions, only they are
much more easily programmed — making them easier to install and use,
much like the hardwired controls they are replacing.
“In
the past, OEMs were forced to choose between simple hardwired controls
or internally developed and designed custom controllers for their
products,” wrote Shah and Resnick. “In either case, very small systems
often could not justify the cost of a PLC, or similar controller, until the programmable relay became available.”
Programmable relays
are already seeing use in many industries and are seeing adoption in
new applications that previously were cost, technology or size
prohibited. For example, programmable relays are replacing those
aforementioned hardwired timers, counters and cube relays in
applications ranging from ventilator controls in office buildings to
sequential control systems for industrial manufacturing.
“Many
OEMs are migrating their traditional hardwired control designs toward
alternative control systems,” wrote the analysts. “For most OEMs,
programmable relays can serve as a very cost effective controller for
their products due to not only their increased flexibility and reduced
physical size, but also because they offer a lower total cost solution with quicker assembly and installation compared to hardwired controls.”
ARC identified five reasons to choose a programmable relay over hardwired controls:
1) Number of Components:
Because programmable relays come with common control functions built-in
you don’t have to buy separate devices for timing, counting, etc. A
single programmable relay
can replace multiple timers, counters and cube relays, reducing the
number of required components cutting the cost of the new system.
2) Enclosure Size:
A single programmable relay takes up a lot less space meaning you can
reduce the size of the electrical enclosure you are using, cutting the
installation footprint on any controller equipment, freeing up space.
Additionally, because the enclosures are generally made of steel, their
price is subject to the volatility of the commodities market so you
reduce your cost exposure.
Hardwired Controls Electrical Panel
3) Engineering and Configuration Effort: They
make it easier to design and configure the machine or line. Rather than
trying to figure out where you are going to put multiple hardwired
devices, how you are going to power and control them you only have to
do this once. Additionally, simple programming commands based on
hardwired principles eliminates the need for an engineer or trained
programmer to configure it.
Programmable Relay Electrical Panel
4) Manufacturing and Installation Cost:
Installing, wiring and testing a single programmable relay with a
built-in power supply takes a lot less time than traditional wired
controllers. Additionally, fewer connections mean fewer possible points
of failure increasing reliability when operating. Says ARC, “Assembly
and testing of a system with hardwired controls requires a significant
amount of interconnect wiring between individual devices, increasing
material costs such as wire, terminal blocks, wire duct, DIN rail,
etc., and labor costs.”
Wiring and Manufacturing Cost Comparison
5) Maintenance and Modification:
Using programmable relays reduces the amount of time required for
commissioning and maintenance. The integrated display and keypad on a
programmable relay provides alarm messages and I/O status simplifying
troubleshooting and often eliminating the need for a multi-meter or
logic probe, which is used to maintain hardwired controls. Ruland
estimates that programmable relays reduces component costs by up to 30
percent on systems using >5 hardwired devices and installation and
manufacturing cost by more than 50 percent.
“With pressure
mounting to increase production while reducing waste, energy costs, and
maintenance downtime, companies are looking for any advantage they can
get,” he says. “Programmable relays provide a clear step up from the
legacy hardwired systems they are so reliant on.”
::Design World::
Filed Under: Factory automation, Relays, Terminal blocks, PLCs + PACs