The Smart Distributed System (SDS) offers companies that implement
automated assembly lines the opportunity to cost effectively respond
to high growth opportunities and quickly changing market conditions.
Companies in dynamic businesses are continuously faced with changing
capacity, and with ensuring their existing facilities are flexible
and cost-effective. These companies need to continually improve
the information available from their assembly lines, and have pertinent
data available throughout their business systems. Once a system
is installed it also becomes critical to detect and remedy problems
quickly.
This solution describes how control systems based on SDS and personal
computers (PC) (a.k.a. Smart Systems) decrease design and installation
costs, reduce operating costs, and allow the use of an assembly
line sooner than was previously possible. It explains the SDS architecture,
and describes some of the components that make up a Smart System.
The paper closes with real-world examples.
A Smart System, as described herein, is one that uses a personal
computer (PC) and the Smart Distributed System (SDS) as the control
architecture. This is in contrast to using a programmable logic
controller (PLC) and wiring the components to input and output cards
on the PLC. Figure 1 depicts the change that is occurring in the
market for automation systems.
Smart Systems provide a number of benefits, including lower design
costs, reduced installation costs and easier troubleshooting.
Fig. 1 - Summary of Market Trends |
Design costs are reduced because the documentation requirements
are less for a Smart System. In a PLC-based system each wire must
be documented as to its wire number and termination. This can result
in several pages of wiring diagrams. Smart System documentation
typically includes a layout drawing for each bus in a system. These
drawings show the location of each device on the bus. In many cases,
the documentation requirements are cut in half.
While smart components cost more than standard ones, the savings
gained during installation outweigh the increased hardware cost.
The total installed cost of Smart Systems is often 20%-30% less
than traditional PLC-based systems. The majority of the savings
are a result of the speed in which a Smart System can be commissioned,
resulting in significantly lower installation costs. Using a PC
that is running the Windows NT operating system also makes it easier
to connect an assembly line to a plant-wide network using industry
standard protocols and interfaces, such as Ethernet and Microsoft
networking.
Rapid deployment results in two more benefits: use of the assembly
line and a faster return on the investment. In most businesses,
being able to use an assembly line a few weeks earlier can have
a notable impact on financial results, particularly if a company
is in need of capacity. Anytime an investment can generate cash
flow sooner it has a positive financial effect.
After a Smart System is installed it continues to provide benefits
to the user. The savings incurred during installation apply when
changing and/or adding to a line. Adding workstations, reconfiguring
a transfer, or extending the line take less time with a Smart System.
When a problem does occur during operation, Smart Systems make
it easier to locate the problem. Smart components are equipped with
diagnostics, and the PC controller has the ability to report them,
including whether a device is missing. Knowing the exact location
of a component that is having a problem can reduce troubleshooting
to a quick glance at a monitor.
SDS is a robust component-level network that allows industrial
devices to be connected on a single cable instead of running individual
control wires to each device.
The SDS specification was created in 1992 by Honeywell’s
Sensing and Control division, a leading supplier of sensors and
switches in the industrial market, and is open to anyone who wishes
to develop SDS-compatible products. Because the SDS specification
is open it has been widely applied.
The definition of a component in SDS is flexible. It can be as
simple as a limit switch, and as complex as an adjustable frequency
drive or bar code scanner. There are even companies using SDS to
communicate with distributed embedded computers doing dedicated
control tasks.
Using Smart components instead of wiring standard control devices
to an I/O block or card provides a number of important benefits,
both during installation and after a line has been commissioned.
Reduced Design Costs
One objective when implementing a Smart System is to eliminate
terminations of wires. Documentation of the electrical system can
be reduced to a single-line drawing show where a bus runs and the
component locations. The volume of documentation is roughly half
of a typical PLC-based system, and the time required to generate
the electrical drawings is one-third.
Installation Savings
The most obvious savings during installation is the reduced wiring
cost, including labor and the wire itself. A simple comparison would
be to compare an installation of 64 sensors. In a PLC-based system,
64 sensors would require 66 wires (2 for power and 64 signal lines),
with varying lengths of wiring runs. Each wire needs to land on
a terminal block, requiring someone to strip the wire, label it,
and insert it in a terminal. This also requires each termination
to be documented.
Installing Smart sensors requires giving a device an address and
attaching it to the bus. Since quick-connect cables are typically
used, there are not be any wiring connections required, depending
on the components used. Each cable is typically labeled with its
address on the bus.
Financial Benefits
Not as obvious, yet potentially much more financially rewarding,
is the speed in which a Smart System can be installed. If a manufacturer
is in need of capacity, getting to use a line quickly can result
in millions of dollars in shipped product. This benefit often far
outweighs the cost savings incurred during the actual installation.
Rapid deployment also means a company's investment can begin generating
positive cash flows sooner.
Productivity Enhancements
The benefits of a Smart System don’t end at installation.
Reduced downtime, changes and additions to the line, and the ease
which real-time production information can be communicated throughout
the facility improve the value of a Smart System.
Downtime is reduced through a set of easy to use diagnostics. When
using a PC with Think & Do Software the health of the SDS network
and the components on the network can be presented in an easy-to-understand
format. If a component is missing from the bus, or has an internal
error, the HMI can be configured to display the error. This eliminates
endless hours of identifying where a problem resides, allowing a
system to be brought back online quickly.
The design and installation savings apply when making changes to
the system. It is just as simple to add components to a system as
it is to initially install them.
Because Smart Systems are based on a PC, connecting the control
system to the plant information system is straight-forward. Think
& Do Software includes servers for OLE for Process Control (OPC)
and Dynamic Data Exchange (DDE). Think & Do also conforms with
the Microsoft Distributed Component Object Modeling (DCOM) specification.
By following several standards, Think & Do has provided one
of the simplest platforms for connectivity available on the market
today.
