By Mike Hannah, Rockwell Automation
Industrial operations are becoming larger and ever more complex, and that’s putting new demands on input/output (I/O) data transmission. Today’s plants are running multiple machines on multiple lines – and in some cases across multiple buildings – for a single operation. On top of this, the technologies used on those machines are growing in number and sophistication.
Legacy netwrks with only a small number of I/O modules and other devices are being replaced with complex networks that have hundreds of I/O modules. Plant operators now have thousands – if not tens of thousands – of sensors and actuators that are sending and receiving increasingly more advanced I/O signals to and from controllers. Single machines can today find the need for >500 individual I/O control nodes on their network.
This all adds up to more and more demand for transmitting mission critical communications, whether it’s across a single machine or across a multi-site production operation. Keeping up with this flurry of information is crucial if a manufacturer wants to minimize downtime and optimize productivity.
Think of I/O data communication as being similar to using a phone – you need to establish a connection at the other end of the line, and you need communication transmitted clearly and correctly. There are a range of factors that can impact the quality of the conversation. Interference or a poor connection, for example, can make communication difficult. Additionally, too many calls being placed in a single area can overload the system and make communication nearly impossible – as is often described during emergencies.
Networks trying to send an ever-increasing amount of I/O communications face similar challenges. They need to ensure signals are sent and received at the other end, and they need to ensure there are no gaps or disturbances within the communication process. Enter the robust and future-proof network architecture: EtherNet/IP, which is standard, unmodified Ethernet with the Industrial Protocol.
Meeting Growing Demands
EtherNet/IP features an active infrastructure and can accommodate an almost infinite number of nodes to give manufacturers optimal flexibility when either designing their networks at the onset or expanding them in the future. Networks with a passive infrastructure, on the other hand, are limited in both the number of devices that can be connected and how they can be connected.
This is more important than ever given the exponential growth in the volume of data that’s flowing out of machines and industrial sites as a whole.
Consider a photoelectric sensor. Two decades ago, this sensor would be providing a single piece of information: on/off. One decade later, that increased to about three pieces of information: on/off, warning and failed. Today, dozens of pieces of data can come from a single photoelectric sensor: on/off, about to switch, distance, signal quality, light warnings, cable warnings, etc.
Just imagine the amount of information that could be coming from that sensor in the next 10 years. Plant operators need to keep this in mind as they design their network architectures not only for the plants of today but, more importantly, for the plants of tomorrow.
In parallel to the growing range of data coming from sensors and actuators, more intelligence is being built into I/O modules. This is enabling decision making to take place closer to the sensors and actuators, but it’s also adding to the communications burden on the I/O. There’s a need, for example, for peer-to-peer communications between I/O modules, as well as for increased configurability and programmability in those modules.
A proprietary network technology can restrict a network architecture with gateways and application software that may force data to go through other specialized devices rather than sending it straight to its intended destination.
Conversely, open, standard network technology like EtherNet/IP enables the free flow of information, without any restrictions. This opens the door for plants to easily integrate more innovative and complex sensors and actuators into their operations. It also enables people to interact directly with sensors and actuators.
In a flexible manufacturing operation, imagine embedding production instructions directly into controller inputs such as RFID tags. As a product moves down the line and/or across facilities, it can tell machines how to build it. Concurrently, in a batch-processing application, an input could be a human operator telling a controller that he or she has manually added an ingredient. That manual information can be tied in with data coming from the weigh scales.
In short, an open, standard network infrastructure allows you to think much more broadly about the inputs and outputs in your control system.
Another important benefit that the EtherNet/IP network architecture brings to I/O is its ability to tell I/O modules how it wants to receive communications. EtherNet/IP enables three different forms of I/O communication that can be preconfigured based on the need. These three communication styles are:
- Periodic – The input module sends a sensor’s status at a predictable and predefined rate of time, typically every 1 to 10 milliseconds. This is the most commonly used communication variation with EtherNet/IP, as it provides a balance between data integrity and traffic optimization on the network.
- Change of state – A device only sends data when a change occurs. This is used in applications in which a device’s status largely remains unchanged.
- Polled – A controller polls devices regarding their input statuses.
The polled communication style is used in traditional I/O systems but is a relatively inefficient model because a device has to wait to be asked for data. Periodic communication, on the other hand, enables a controller and an I/O module to agree how often the data will be sent at the establishment of the connection. It’s then the responsibility of each device to send its information when it’s needed.
EtherNet/IP when used with periodic communications takes another step in scalability by allowing every device on the network to communicate at a different rate – the motion control amplifier may need updating every millisecond (or more); the temperature transmitter on a tank is unlikely to see changes more often than every 100ms; the Ethernet infrastructure with only fault diagnostics will hopefully never change states. The devices communicate at the optimum rate for their own function, reducing network burden.
In today’s plant systems, there are more inputs that are associated with device diagnostics and prognostics than there are with the state of the actual products being produced. Devices are monitoring their own health and feeding that information to controllers. That enables three different things to happen:
- The controller can include the device’s health status as a factor in the decision it makes
- Asset-management systems can schedule direct maintenance actions
- Safety-protection systems can ensure that systems are operating in safe states
This diagnostic and prognostic data can be crucial to maximizing machine uptime and optimizing overall operations, and it’s only expected to increase. With this growth in data will be an increased need to carry it to the system in the form on inputs.
Plant operators will need to be prepared for this growth in diagnostic data just as they will for process and control data – with an active network architecture that enables the integration of new technologies and doesn’t restrict the flow of data.