Image Processing Reference
In-Depth Information
TABLE .
Impact of Process Attributes on Wireless Technologies
Process Attribute
Description
Impact on Wireless Technology
Device types
Predominant or common mix of
devices, e.g., analog and/or
discrete devices
Thetypeofdata(andconsequentlyalsoamount)
that is sent has a major impact on the design of
the communication protocol.
This in combination with the timing requirements
sets boundaries on the frame/package size
utilized.
Device count per unit
Typical number of devices in a
manufacturing unit/production
cell
The number of devices in a plant, their geographic
distribution has a dramatic impact on the
communication technology.
The ability to cover a whole factory with wireless
communication depends on a number of factors
such as
Unit physical size (m)
The physical size of the a typical
manufacturing unit/production
cell
●
Range of the wireless device/network, which is
governed in turn by the reliable operation range,
the disturbing range, and “frequency reuse” range
Units per plant
Number of manufacturing units/
production cells in a typical plant
●
Number of wireless nodes per manufacturing
unit
●
Number of coexisting wireless networks within
reliable operation range without performance
degradation
Device density (units per m
)
Number of devices per m
Devices per plant
Number of devices in a typical
plant
Production cycle length
Length of a typical production
cycle
The production cycle length and startup times have
a direct impact on the setup times for the wireless
networks, such as network forming and
adding/removing nodes.
Unit startup time
Startup time of a manufacturing
unit/production cell
Time: fast/subunit
Fast internal communication
needs, e.g., drives loop
This attribute in combination with the node
density has the greatest impact on the technology
selection.
Depending on the required update rate and equally
important the latency (variation in
communication delay), very radical differences in
design of the wireless communication solution
might be required.
Control loop
Time resolution of normal
control loops
Slow/diag./HMI
Time resolution for noncritical
data such as diagnostics or HMI
Field device cost
Typical cost of the field devices
The cost of the device to a large extent puts some
upper barriers on the target cost of the wireless
communication solution.
Installation cost/device cost
Cost of the installation in
comparison to the cost of
installing the device
This metric provides guidance on the target cost of
installing and setting up the wireless
infrastructure.
Automation technology
Type of control system utilized to
automate the process
The use of a DCS vs. e.g., a PAC/PLC solution, to
some extent governs the logical network
structure. This is also reflected in the device
count and unit count measures listed above.
Commonly used device networks
Typical wired infrastructure in
today's plants
At some point, the wireless network has to interface
with the existing network infrastructure. The
employed wired network technology and topology
have an impact on the way one could/should
integrate the wireless system in the plant.
Power availability
Availability of line power/battery
size/energy harvesting
The amount of energy that is available has a
dramatic impact on the design of the wireless
protocol (energy efficiency), as well as the
possible duty cycle of the application.
. Component selection to a large extent follows the choice of technology, but is many times
already “given” by the platform choices of existing legacy systems.
. Finally when designing, implementing, and testing the device, we need to pull all
the bits together. This usually requires quite an iterative process with many trade-offs
and redesigns due to a combination of inaccurate or incomplete requirements and/or
component specifications.
