ControlNet is a real time control network which has robust, deterministic and secure features for challenging industrial automation applications. Popularly known as fieldbus, this open network protocol, originally developed by Rockwell Automation is a member of the CIP (Common Industrial Protocol) network family. Earlier it was carried by ControlNet International, but now the whole supervision and organization of ControlNet has been transferred to ODVA, (an association responsible for management of all protocols in the Common Industrial Protocol family).
Combining utilities of an I/O network and a peer-to-peer network, the ControlNet network using Common Industrial Protocol offers high speed performance and repeatable transfers of data in both areas. A unique physical layer based on RG-6 coaxial cable with BNC connectors is defined by ControlNet whose signaling is based on Manchester code at 5 Mbit/s. Unlike other fieldbuses, ControlNet has a built in support for fully redundant cables and above all the communication over ControlNet takes place in an exactingly scheduled and well deterministic way.
For configuration purpose each ControlNet device requires electronic device data sheets (i.e. EDS-Files containing electronic descriptions, all relevant communication parameter and objects of the ControlNet device) which are provided by the device manufacturers. Also an exclusively available configuration tool e.g. Rockwell’s RSNetWorx need to be employed during the initial setting phase of the ControlNet network for configuring ControlNet Master Scanner.
ControlNet supports both scheduled and unscheduled transfers
Time critical data is scheduled data and deterministic and repeatable transfers that are continuous and asynchronous to the ladder logic program scan are called Scheduled data transfers. It occurs at a consistent rate that is either at the same or faster than the rate specified in an I/O map-table entry.
Non-time critical data is unscheduled data and non-deterministic data transfers through ladder-initiated communication or programming devices are known as unscheduled transfers. A ControlNet network allows unscheduled messaging when deterministic delivery is not required. Unscheduled operations include unscheduled non-discrete I/O data transfers through ControlNet I/O Transfer instructions (CIOs)in the PLC ladder program and peer-to-peer messaging through Message instructions (MSGs) in the PLC ladder program. Unscheduled transfers are performed during the unscheduled time in the network update interval. Number of nodes, application program, Network Update Time(NUT), etc. help determine how much time there is for unscheduled messaging.
Network Update Time (NUT)
It is the repetitive time interval in which data can be transmitted over the ControlNet network. Data cannot transfer faster than NUT.
Some of the significant features of ControlNet networks which make them stand apart from other fieldbuses are listed below:
- Implements programming, processor-to processor interlocking, and I/O control on the same link without impacting time-critical I/O
- Offers media options to fit our application needs including copper, fiber, fiber ring, media redundancy, and intrinsically-safe.
- Provides improved I/O performance and controller-to-controller interlocking with high-speed data throughput.
- Supports a maximum of 99 nodes, with no minimum distance between nodes.
- Availability of Simple and flexible installation options.
- Access the network from any node for PLC processor programming and troubleshooting.
- Improved network efficiency with Multicast of inputs and peer-to-peer data.
- Deterministic, repeatable transfers of data to/from digital and analog I/O.
- Producer / Consumer services let you configure devices, control, and collect information over a single network.