Transcript Chapter 11 Intro to ControlNet

Chapter 11
Introduction To ControlNet
Networks Popularity
• Stand-alone PLCs fading fast
• Older networks being upgraded
– Faster more efficient networks
– New networks offer deterministic and
repeatable data transfer
Network Advantages for
Maintenance Individuals
• PLCs connected on network
– Access any PLC from a single computer
anywhere on the network
– Upload, download, on-line editing across
network to any device on network from a
central location
ControlNet
• Open network managed by ControlNet International
• Use for real-time data transfer of time-critical and
non-time-critical data between processors or I/O on
same link
• Data transferred at a fixed rate of 5 million bits per
second
• ControlNet basically a combination of AllenBradley’s Data Highway Plus and Remote I/O
ControlNet Nodes
• Up to 99 nodes
• No node 0
• Actual number of nodes determined by how
efficiently the network bandwidth is set up
• Network set up using RSNetWorx for
ControlNet software
Nodes on ControlNet
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•
•
•
SLC 500, ControlLogix, PLC 5 processors
Third-party field devices
Operator interface
Variable frequency drives
ControlNet Applications
• ControlLogix processor, SLC 500, or PLC 5
processor scheduled data exchange
• Local PLC connection to remote chassis for
high-speed remote I/O connectivity
Interlocking or Synchronization
of Multiple Nodes
• Synchronized starting of variable frequency
drives on ControlNet
• Interlocking multiple processors
Network Bridging
• Connect two Data Highway Plus networks
• Connect multiple DeviceNet networks
Trunk Line – Drop Line
ControlLogix PLCs
Operator
interface
Trunk line
Node
number
Termination
resistor
Termination
resistor
Control Net Tap
Drop line
Variable
frequency drive
as node 4
PLC 5 as
Computer
Interface cards node 7
SLC 500
as node 8
ControlNet Taps
Straight T
Straight Y
Right Angle
Right Angle Y
Drop line length is fixed at 1 meter (39.5 inches).
SLC 500 ControlNet Interface
• 1747-SCNR
• SLC 500 modular
PLCs
• Scheduled and
unscheduled
messaging
ControlLogix ControlNet Interface
• 1756-CNB
– Channel A only
• 1756-CNBR
– Channel A and B for
redundant media
• Module node address
set with side switches
• Duplicate node
addresses not allowed
• NAP for computer
connectivity
FlexLogix ControlNet Interface
Two ControlNet interface cards
with redundancy
FlexLogix processor
Two communication card slots
NAP
Set node address here
Redundant Media
Personal computer
with ControlNet
interface
ControlLogix
Trunk
line
Redundant
cables
Tap
Drop
line
PLC 5
node
Personal Computer Interface
Personal computer with ControlNet
interface card like 1784-KTCX15
Redundant
trunk line
KTCX15 ControlNet Interface
Status indicators
Network access port
Channel A
Channel B
Floppy with card driver
KTCX15 Interface to PLC 5
PLC 5 ControlNet
processor
NAP
Channel A
Channel B
Redundant
trunk line
Personal Computer to NAP
Personal computer with
ControlNet interface
NAP connection
Redundant
trunk line
ControlNet Cabling
ControlNet Segment
Cabling Terms
•
•
•
•
Segment
Trunk line cable section
Termination resistor
Link
Segment
• Comprised of a number of sections of trunk
cable separated by taps
• Maximum segment length 1,000 meters or
3,280 feet
• Maximum 48 nodes per segment
• Segment length determined by number of
nodes
Taps
• Taps are required.
• There is no minimum cable length between
taps.
• Taps can be directly connected together.
Trunk Line Cable Section
• Trunk line cable section connects one tap to
another.
• Taps are required.
• Standard light industrial quad shielded RG-6.
• Special use cables are available.
• Fiber optic cables are available.
Termination Resistor
• One termination resistor is required on the
end of every segment.
ControlNet Segment
Segment
Termination
resistor
Termination
resistor
Tap
Trunk
line
Drop
line
39.5
inches
Segment Calculation
• Formula to calculate segment length
1,000 meters – [16.3 meters ( number of taps – 2)]
Calculation Example:
• Calculate maximum segment length using
standard light industrial RG-6 coax requiring
22 taps.
1,000 meters – [16.3 meters ( 22 - 2)]
1,000 meters – [16.3 meters ( 20 )]
1,000 meters – 326 meters
Maximum segment length = 674 meters
ControlNet Link
• If more than 48 nodes are required, an
additional segment is required.
• Repeater connects segments.
• Two segments connected by a repeater is a
link.
Three Segments Connected by a
Repeater to Create a Star
Four Segments Connected by
Repeaters to Create a Ring
ControlNet Repeaters
• Required if additional nodes are required
after either maximum number of nodes or
cable length reached
• Two modules required to build a repeater
• Many copper and fiber repeaters to select
from depending on application
Building a Repeater Example
• The two repeater modules can be DIN railmounted as a pair to build a repeater.
– 1 - 1786-RPA (repeater adaptor module)
– 1 - 1786-RPCD (dual copper repeater)
Repeater Adapter Module
Dual Copper Repeater Module
Repeaters
ControlNet
PLC 5
Add Flex- I/O blocks
to this communication
for remote I/O points
Example of Fiber Repeater
• Fiber repeaters
available as short,
medium, long, and very
long haul
• Up to 18.5 miles
ControlNet network
using proper fiber
repeaters
• Right-hand module in
previous slide
RSNetWorx Software
RSNetWorx
• From Rockwell Software
• Required to configure and schedule a
ControlNet network
RSNetWorx For ControlNet
RSNetWorx
for ControlNet
Go on-line
with network
Network
bandwidth
utilization
Enable
editing
Manual
network
configuration
Graphic view
of network
Trunk
line
Node
number
How Critical is this Data?
• Separate data into two categories.
– Is this information time critical?
– Can this information be transferred on a nontime critical basis?
What is Real-Time
for This Application?
• How soon do you really need the
information?
• Networks do not have unlimited bandwidth.
– Cannot have everything instantly
Realistic Data Flow (1 of 2)
• Assume you had a tank that takes four hours
to fill.
– Why would you need a tank level every 10
milliseconds?
– What is realistic?
– Would every few seconds be acceptable?
Realistic Data Flow (2 of 2)
• Assume you had a tank of water that takes
two hours to heat.
– Why would you need a tank temperature
every 10 milliseconds?
– What is realistic?
– Would every few seconds be acceptable?
Scheduled / Unscheduled
• Time critical data is scheduled data.
– Requested packet interval (RPI) set up in
RSNetWorx
• Non-time critical data is unscheduled data.
– Message instruction programmed on PLC
ladder rung
• Trigger to transfer only when needed
RPI
• Requested packet interval
• Scheduled network service
– The requested interval time-critical data will
flow
– ControlNet will meet or beat the RPI if network
installed and configured properly
Inefficient Network
• Improper installation
– Follow installation manual
• Improper network modification
– Follow installation manual
• Poor design
– Follow installation manual
• Overdriving network
– Unrealistic data flow expectations
ControlNet Bandwidth
• Three pieces to bandwidth
– Scheduled traffic
– Unscheduled traffic
– Maintenance or guard band
Network Update Time
Scheduled Traffic
Unscheduled
Traffic
Network
Maintenance
Network Update
• One cycle of the network
• Called NUT time
– Set up on RSNetWorx
• Data cannot transfer faster than the NUT
Scheduled Maximum Node
• SMAX
• This is the highest node number that will be
allowed to send scheduled data.
• Any node address above SMAX that has
scheduled data to transfer will not be allowed
to transmit.
Unscheduled Maximum Node
• UMAX
• This is the highest node number that will be
allowed to send unscheduled data.
• Any node address above UMAX that has
scheduled data to transfer will not be allowed
to transmit.
Node Can Send Both
• A node can send scheduled as well as
unscheduled data/
• The node number must be within SMAX.
Slot Time
• Slot time is time the network spends waiting
for a node to respond when the node address
is either not used or the node is not
responding.
• Unused node addresses should be kept to a
minimum for network efficiency.
RSNetWorx Parameters
NUT
SMAX
UMAX
Media and
channel information
Set-up Example
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10 nodes scheduled traffic
2 spare nodes future scheduled traffic
14 unscheduled nodes
3 nodes for NAP connectivity
– What will SMAX be?
– What will UMAX be?
– What about slot time?
– Maximum cable length?
Maximum Segment Length
• Assume RG-6 coax
– How many taps?
Number of Taps
• Number of taps does not include NAP
connections.
• No node 0 in ControlNet.
• To keep it simple, let’s use taps as nodes 1 to
26.
– NAP nodes 27, 28, 29
– Total taps = 26
Segment Calculation
• 1,000 meters – [16.3 meters( Number of taps
– 2)]
• 1,000 meters – [16.3 meters( 26 – 2)]
• 1,000 meters – [16.3 meters( 24 )]
• 1,000 meters – 391.2 meters
• Maximum segment length 608.8 meters
SMAX
• Scheduled traffic nodes 1- 12
• Nodes 1-10 currently used
• Nodes 11 and 12 future scheduled
– Unused nodes = slot time
• SMAX set at 12
Determine UMAX
• Nodes 13 - 26 unscheduled traffic
• Nodes 27, 28, 29 for NAP
– RSLinx drivers for personal computer node
addresses MUST be set at 27, 28, or 29.
– RSLinx default for 1784-PCC personal
computer interface default = node 99.
• UMAX must be set at a minimum of 29.
Efficient Network Configuration
SMAX= 12
UMAX =29
1
99
Node
10
Node 11 & 12
future scheduled
Node 27, 28, 29
for NAP
Future Network Expansion
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•
•
•
Recalculate segment length?
Reconfigure SMAX?
Reconfigure UMAX?
Reschedule network using RSNetWorx if any
scheduled node is added or modified.
Reschedule Network
• It must be done whenever a scheduled node
is modified or added to the network.
• Network configuration is scheduled in
RSNetWorx for ControlNet.
– Part of saving new network configuration
– ALL processors on network in program mode
– Referred to as optimizing and rewriting
network configuration
Rescheduling and the Keeper
• The ControlNet communication module at the
lowest node number is called the keeper.
– Should be node 1
– For ControlLogix 1756-CNB(R)
– Keeper like a traffic cop
• Directs traffic on network and synchronizes nodes
– Newer CNBs have multi-keeper capability
Multi-keeper
• Older CNBs are single-keeper networks.
– Newer CNBs support multi-keeper.
– If there was a newer CNB at node 1 and also
at node 2, node 1 would be the keeper and
node 2 would be a “back-up” keeper.
– If node 1 fails, node 2 would take over
network traffic control.
– In single-keeper systems, if the keeper fails,
all network communications are lost.