Introduction To ControlNet

1
Chapter 11

• Introduction To ControlNet

2
Networks Popularity

• Stand-alone PLCs fading fast
• Older networks being upgraded
• Faster more efficient networks
• New networks offer deterministic and repeatable
  data transfer

3
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

4
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
  Allen-Bradleys Data Highway Plus and Remote I/O

5
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

6
Nodes on ControlNet

• SLC 500, ControlLogix, PLC 5 processors
• Third-party field devices
• Operator interface
• Variable frequency drives

7
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

8
Interlocking or Synchronization of Multiple Nodes

• Synchronized starting of variable frequency
  drives on ControlNet
• Interlocking multiple processors

9
Network Bridging

• Connect two Data Highway Plus networks
• Connect multiple DeviceNet networks

10
Trunk Line Drop Line
ControlLogix PLCs
Operator interface
Trunk line
Node number
Termination resistor
Termination resistor
Control Net Tap
Drop line
SLC 500 as node 8
PLC 5 as node 7
Variable frequency drive as node 4
Computer Interface cards
11
ControlNet Taps
12
SLC 500 ControlNet Interface

• 1747-SCNR
• SLC 500 modular PLCs
• Scheduled and unscheduled messaging

13
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

14
FlexLogix ControlNet Interface
Two ControlNet interface cards with redundancy
FlexLogix processor
NAP
Two communication card slots
Set node address here
15
Redundant Media
Personal computer with ControlNet interface
ControlLogix
Trunk line
Redundant cables
Tap
PLC 5 node
Drop line
16
(No Transcript)
17
Personal Computer Interface
Personal computer with ControlNet interface card
like 1784-KTCX15
Redundant trunk line
18
KTCX15 ControlNet Interface
Status indicators
Network access port
Channel A
Channel B
Floppy with card driver
19
KTCX15 Interface to PLC 5
PLC 5 ControlNet processor
NAP
Channel A
Channel B
Redundant trunk line
20
Personal Computer to NAP
Personal computer with ControlNet interface
NAP connection
Redundant trunk line
21
ControlNet Cabling

• ControlNet Segment

22
Cabling Terms

• Segment
• Trunk line cable section
• Termination resistor
• Link

23
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

24
Taps

• Taps are required.
• There is no minimum cable length between taps.
• Taps can be directly connected together.

25
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.

26
Termination Resistor

• One termination resistor is required on the end
  of every segment.

27
ControlNet Segment
Segment
Termination resistor
Termination resistor
39.5 inches
Trunk line
Drop line
Tap
28
Segment Calculation

• Formula to calculate segment length

1,000 meters 16.3 meters ( number of taps 2)
29
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
30
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.

31
Three Segments Connected by a Repeater to Create
a Star
32
Four Segments Connected by Repeaters to Create a
Ring
33
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

34
Building a Repeater Example

• The two repeater modules can be DIN rail-mounted
  as a pair to build a repeater.
• 1 - 1786-RPA (repeater adaptor module)
• 1 - 1786-RPCD (dual copper repeater)

35
Repeater Adapter Module
36
Dual Copper Repeater Module
37
Repeaters
ControlNet PLC 5
Add Flex- I/O blocks to this communication for
remote I/O points
38
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

39

• RSNetWorx Software

40
RSNetWorx

• From Rockwell Software
• Required to configure and schedule a ControlNet
  network

41
RSNetWorx For ControlNet
Go on-line with network
RSNetWorx for ControlNet
Network bandwidth utilization
Enable editing
Graphic view of network
Manual network configuration
Trunk line
Node number
42
How Critical is this Data?

• Separate data into two categories.
• Is this information time critical?
• Can this information be transferred on a non-time
  critical basis?

43
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

44
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?

45
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?

46
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

47
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

48
Inefficient Network

• Improper installation
• Follow installation manual
• Improper network modification
• Follow installation manual
• Poor design
• Follow installation manual
• Overdriving network
• Unrealistic data flow expectations

49
ControlNet Bandwidth

• Three pieces to bandwidth
• Scheduled traffic
• Unscheduled traffic
• Maintenance or guard band

50
Network Update Time
Scheduled Traffic
Unscheduled Traffic
Network Maintenance
51
Network Update

• One cycle of the network
• Called NUT time
• Set up on RSNetWorx
• Data cannot transfer faster than the NUT

52
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.

53
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.

54
Node Can Send Both

• A node can send scheduled as well as unscheduled
  data/
• The node number must be within SMAX.

55
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.

56
RSNetWorx Parameters
NUT
SMAX
UMAX
Media and channel information
57
Set-up Example

• 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?

58
Maximum Segment Length

• Assume RG-6 coax
• How many taps?

59
Number of Taps

• Number of taps does not include NAP connections.
• No node 0 in ControlNet.
• To keep it simple, lets use taps as nodes 1 to
  26.
• NAP nodes 27, 28, 29
• Total taps 26

60
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

61
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

62
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.

63
Efficient Network Configuration
UMAX 29
SMAX 12
1
99
Node 10
Node 11 12 future scheduled
Node 27, 28, 29 for NAP
64
Future Network Expansion

• Recalculate segment length?
• Reconfigure SMAX?
• Reconfigure UMAX?
• Reschedule network using RSNetWorx if any
  scheduled node is added or modified.

65
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

66
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

67
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.