Advances in intelligent motor control centres now allow for the detailed diagnostics needed to improve maintenance schedules and reduce downtime. Sean Ottewell reports.
Keeping manufacturing processes running smoothly often hinges on the ability of engineers to access real-time production data. Fortunately, advanced monitoring and sensing technologies that integrate smart devices, device-level networks and software into motor control centres now exist, allowing manufacturers to capture and use equipment and process data.
Today's intelligent motor control centres (MCCs) offer a textbook example of this, with an integrated design that delivers real-time monitoring and detailed diagnostics to help improve productivity and maximise critical asset availability. These systems occupy a prominent role in control schemes, housing a comprehensive array of control and monitoring devices, and a built-in network that opens up access to process data from virtually every corner of the plant.
MCCs have moved rapidly to include the latest component technologies. Integrating these advanced technologies presents a major opportunity for manufacturers to transform islands of data into useful information.
Now Rockwell Automation has published a white paper which explains how advanced MCCs provide process application users with critical information that ultimately helps to minimise - and prevent - downtime.
Intelligent Motor Control Centres Lay the Foundation for Improvements in Manufacturing Efficiency and Reliability provides an overview of the industry drivers and evolution of MCCs, including technology considerations, configuration methods, networking advantages, as well as costs and benefits gained from real-world application examples.
The intelligent MCC
Distinguishing itself from a standard unit, the intelligent MCC integrates three major system components - communications, hardware and software. While early versions of MCCs with communication networks contained variations of these elements, today's solutions leverage a harmonised design that deliberately integrates these elements into a unified solution.
Furthermore, with a lower installation cost than traditional MCCs, plus the protective, monitoring and troubleshooting advantages, integrating intelligent MCCs presents a major opportunity for manufacturers to capture and use equipment and process data to improve productivity and maximise asset availability (Fig. 1).
Traditionally, MCCs consisted of primarily electromechanical components with hard-wired connections. These components remain the workhorses of MCCs, but advances in solid-state technology are ushering in a wave of more intelligent, programmable devices that do more than just turn on and off a motor. These include variable frequency drives, solid-state starters and electronic overload relays. Today's MCCs monitor motor current and thermal capacity, perform protective troubleshooting functions, and provide detailed diagnostics to help avert downtime. Distinguishing itself from a standard unit, the intelligent MCC integrates three major system components - communications, hardware and software.
A reliable, robust network
The communication network lies at the heart of an intelligent MCC. Therefore, it's important to implement the right network. The trend toward open networks offers clear and well-documented advantages.
In general, the network should provide adequate throughput (up to 500 kbps), offer a low cost per node, and be accepted by a wide range of suppliers and users. The best choice is a robust, reliable network, such as DeviceNet, which provides ease of configuration advantages and superb diagnostic capabilities.
Users also should consider differences in network media. Because of the way data is handled for various applications, most facilities require multiple networks. However, providing seamless communication from one network to the next can present a major obstacle when using different network protocols.
Using a range of network protocols is similar to dialing a three-way telephone call from the US to extensions in France and Japan. Just because the phone rings on the opposite end and someone answers doesn't mean all parties can understand one another without a translator. A common language is needed for conversation.
This is where a common application layer, such as the Common Industrial Protocol (CIP), proves to be a major differentiator. CIP is a single, media independent platform that provides seamless communications between plant-floor devices and enterprise-level systems. This allows manufacturers to integrate control, configuration and data collection across multiple networks, getting real-time information to where and when it is needed.
The CIP networks including DeviceNet, ControlNet and EtherNet/IP - are open networks that share the CIP at their upper levels while remaining media independent at lower levels. This allows manufacturers to specify the best network for each application and eliminate costly gateways when connecting dissimilar upper-level networks. More importantly, it opens the door to system-wide communication while offering better tools to control motors and increase plant efficiency.
When properly deployed, the intelligent MCC allows users to monitor and analyse operations from anywhere at any time. With access to more detailed information over longer periods of time, users can better predict potential problems and prevent catastrophic failures.
For maximum network efficiency, engineers can configure devices to report data as often and in whatever format as needed.
For example, a drive controlling a rapidly fluctuating process might report status every 50 milliseconds, while a motor on a slower changing process may only be required to report status every 60 seconds.
For most parameters, devices can be configured to communicate only on a change of state. Diagnostic data can be accessed outside of the regular data scan, keeping all data available without clogging the network with information that's only used occasionally.
Information reported by devices in the system can be recorded for later analysis, if needed, or used to generate alarm messages as important events occur in the process.
Up until now, MCCs lacked interwiring and required extensive field wiring, documenting, testing and system integration. Conversely, the intelligent MCC arrives preconfigured, pretested and ready to install. The communication cables are installed and tested, intelligent devices are preprogrammed and software screens are pre-configured, all of which help reduce start-up time.
The primary drawback of many network configurations, such as those in a daisy-chain configuration, is the inability to make device changes or additions without shutting down the network.
With this type of topology, moving or adding devices requires the technician to break the chain, thus disabling the network.
A better approach is to isolate trunk and drop lines behind barriers, avoiding potential damage to communication cables during installation and maintenance activities.
Trunk and drop network design provides easy-connection communication ports that allow devices to be plugged or unplugged without network disruption. This configuration should also provide independent, readily accessible ports to simplify installing, withdrawing, relocating and adding plug-in units.
Engineers require detailed documentation for fast start-up and efficient troubleshooting, but this documentation is often misplaced or incomplete With an intelligent MCC, users can access electronic documentation on the same PC running the monitoring software.
A prime opportunity
As the cost of intelligent devices continues to decline, intelligent MCCs offer manufacturers an excellent opportunity to benefit from advanced technology of these control systems, including improved diagnostics, increased system reliability, design flexibility and simplified wiring. While a robust, reliable design is critical for helping to contain faults and minimis downtime, equally important is the device-level networking capabilities of today's intelligent MCCs.
For a copy of the white paper, visit http://samplecode.rockwellautomation.com/idc/groups/literature/documents/wp/mcc-wp001_-en-p.pdf.