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Chapter 11

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

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Chapter 11

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  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-Bradley’s 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. Straight Y Right Angle Right Angle Y Straight T Drop line length is fixed at 1 meter (39.5 inches). 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. Personal Computer Interface Personal computer with ControlNet interface card like 1784-KTCX15 Redundant trunk line

  17. KTCX15 ControlNet Interface Status indicators Network access port Channel A Channel B Floppy with card driver

  18. KTCX15 Interface to PLC 5 PLC 5 ControlNet processor NAP Channel A Channel B Redundant trunk line

  19. Personal Computer to NAP Personal computer with ControlNet interface NAP connection Redundant trunk line

  20. ControlNet Cabling ControlNet Segment

  21. Cabling Terms • Segment • Trunk line cable section • Termination resistor • Link

  22. 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

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

  24. 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.

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

  26. ControlNet Segment Segment Termination resistor Termination resistor 39.5 inches Trunk line Drop line Tap

  27. Segment Calculation • Formula to calculate segment length 1,000 meters – [16.3 meters ( number of taps – 2)]

  28. 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

  29. 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.

  30. Three Segments Connected by a Repeater to Create a Star

  31. Four Segments Connected by Repeaters to Create a Ring

  32. 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

  33. 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)

  34. Repeater Adapter Module

  35. Dual Copper Repeater Module

  36. Repeaters ControlNet PLC 5 Add Flex- I/O blocks to this communication for remote I/O points

  37. 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

  38. RSNetWorx Software

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

  40. 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

  41. 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?

  42. 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

  43. 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?

  44. 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?

  45. 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

  46. 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

  47. Inefficient Network • Improper installation • Follow installation manual • Improper network modification • Follow installation manual • Poor design • Follow installation manual • Overdriving network • Unrealistic data flow expectations

  48. ControlNet Bandwidth • Three pieces to bandwidth • Scheduled traffic • Unscheduled traffic • Maintenance or guard band

  49. Network Update Time Scheduled Traffic Unscheduled Traffic Network Maintenance

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