Ch. 6 Industrial Networks and Fieldbuses Review

Data Highway Plus allowed up to 64 nodes on one highway, with speeds up to 230 ______

Data Highway uses +14 volts peak-to-peak signaling, while Data Highway Plus uses +7 volts peak-to-peak ______

The transmission protocol used by most other PLC manufacturers, in addition to their own proprietary method, is the Modbus Remote Terminal Unit ______

Modbus RTU is a query-response ______; that is, only the master can query—the slave cannot initiate, only respond

Many manufacturers use Modbus RTU as an accepted ______ and the protocol can perform the basic host-to-PLC communications

The Modbus protocol originally had two modes: an ASCII mode and the RTU ______

The MAC and Physical layer use idle time as start and stop delimiters, using greater than ______

Data Highway used a modified token-passing scheme known as floating ______, which provided a bid scheme for controllers who wished to be master

Data Highway Plus allows a PC with a KT card and appropriate software to be used as a programming or operator ______

Data Highway could have a trunk line of up to 10,000 ft. at the 57.6 Kbps data rate, with drop lines from the trunk of no more than 100 ______

A distributed control system has ______ defined as a system in which the control functions are shared among separate intelligent devices

A distributed control system has the intelligence located in various nodes that are connected by some media and networked together, enabling the nodes to perform ______ communications and enabling each node to perform a portion of the overall set of tasks

At the low-cost end of industrial control systems, the programmable logic controller , a device developed to replace relay logic, enjoyed significant success in industrial applications. This PLC system was not called a DCS, however, as DCS had come to mean devices capable of performing ______ control actions, rather than just on/off or twostate control

Most instrument manufacturers still sell proprietary DCSs. These systems perform PID control for several loops and offer advanced control strategies such as cascade, feedforward, ratio, and other ______ control strategies

Proprietary DCSs also supply trending, optimization, nice graphics, diagnostics, operator stations, and an engineering workstation for configuration and changes. The first of these DCSs, like the Honeywell TDC2000 and EMC Controls Emcon-D and D/3, had ______ local area networking schemes, as well as proprietary operating systems in both the workstations and operator consoles, particularly in the distributed controllers

It was in the next generation of DCS products in the mid-1980s where systems based on some version of UNIX began to appear. These early systems used ______ LANs to link all of their components

Conventional DCS technology has lost a large percentage of the industrial automation market share to PLC-based offerings, except in specific market segments where the “bumpless” redundancy, advanced control features, and live configuration change capabilities of a DCS are seen as ______

Two such schemes predominated: Allen-Bradley PLCs used variants of the Data Highway and almost every other PLC vendor made use of Modicon’s Modbus protocol. Today, both of these communication schemes have been migrated onto an ______ platform as Application layer protocols and most PLC manufacturers offer Ethernet connectivity

The topology of Allen-Bradley’s Data Highway , Data Highway Plus , and Data Highway 485 is illustrated in ______

Industries usually operate in extremes of temperature, vibration, chemical atmosphere, and electrical interference, as well as in areas that lack ______

Scalable means the design doesn’t lose its efficiency when the network is expanded by an order of magnitude or more. Although additional resources will be required, the overall design must accommodate very small to very large network configurations, with no loss in features and ______

Most operators know their process, however, asking them to learn the intricacies of communications is probably beyond their desires and training. In a properly designed industrial control system, the communications technology will be totally transparent to the operator. He or she shouldn’t have to determine anything network related, except how to report an alarm to the correct ______

An industrial network is three or more devices connected through a shared media or distribution in an industrial environment, including the media, infrastructure, protocols, and all other peripherals and actions necessary for functional communications, particularly between industrial devices. An industrial network is considered to be an industrial network when it connects _____ or more devices through a shared media or distribution in an industrial environment.

Of the numerous industrial networks available, the authors have selected for discussion those that illustrate a type, have a large installed base, and/or offer the authors sufficient technical information. The authors have chosen to discuss industrial networks that illustrate a type, have a large installed base, and/or offer the authors sufficient technical information, among the _____ industrial networks available.

All networks, commercial and industrial, share some common requirements: They must provide effective performance for resources used. Both commercial and industrial networks must meet ______ requirements: They must provide effective performance for resources used.

All designs are compromises, so some of the common requirements may have to give way to ensure meeting key industrial requirements, such as low downtime and so on. In order to meet key industrial requirements, some of the ______ requirements may have to give way.

Industrial requirements are such that network response times must fall within a specific window of time or an error can result. Industrial requirements dictate that network response times must fall within a specific window of time, also known as ______.

In general, the window must be wide enough so that the response can be acted on in real time; that is, the controlling device must issue an output in time to affect the control or alarm before a process’s operation becomes unstable. The window for network response times must be wide enough to allow for real-time action, ensuring that the controlling device can issue an output in time to affect the control or alarm before a process’s operation becomes unstable. This functionality is known as ______.

Time-sensitive operations, such as computing a PID algorithm, must provide a definitive window of time for data input or the results will be incorrect. Computing a PID algorithm and other time-sensitive operations must offer a definitive window of time for data input to avoid ______ results.

If the control system is down, the process is down and the company is losing money. Downtime requirements in modern industry are such that a system must be up above the “five nines”; downtime must be less than 0. The downtime requirements in modern industry demand that a system must be up above the “five nines”; downtime must be less than ______.

Earlier versions of Modbus used different, less effective, versions of the frame check code, but today the standard defines using the ______ check code

HART protocol is a ______ multi-drop

DeviceNet is a low-level network that provides connections between simple industrial devices and ______ devices

ControlNet operates at ______ Mbps

EtherNet/IP uses the Dynamic Host Configuration Protocol and Address Conflict Detection to allow devices to be added and removed from a network. EtherNet/IP supports three types of messages: ______, explicit, and unconnected

LonWorks uses the domain model for addressing four major message types: acknowledged, request/response, unacknowledged, and ______ repeated

LonWorks has found acceptance as a sensor network, a device network, and a ______ network

PROFIBUS DP is a high-speed data communications network for factory automation, while PROFIBUS PA is for the process ______ market

The Physical layer connects the node to the media and provides for activation, deactivation, and maintenance on a ______ basis

The SP50 standard, as implemented by the Fieldbus Foundation, defines types of media, signals, speeds, and topology, including the number of nodes and node ______

Continuous process control requires a moderate ______; speed requirements dictate power consumption

The designers of FOUNDATION Fieldbus decided on a moderately high-speed bus for intrinsic and field instrument work and originally selected two higher speeds for ______ areas

11a, Wireless Systems for Industrial Automation: Process Control and Related Applications, is a wireless networking standard developed by ISA. The ISA100 committee was formed in ______ to establish standards, and related information, that define procedures for implementing, deploying, configuring, and operating wireless systems at the field level in the automation and control environment.

The committee is made up of automation professionals from over ______ companies worldwide and represents all stakeholders.

In 2009, the ISA Automation Standards Compliance Institute established the ISA100 Wireless Compliance Institute, which owns the ISA100 Compliant certification scheme and provides independent testing of ISA100-based products to ensure conformance to the ISA100 standard. The standard was approved by the committee in ______, by ANSI in 2011, and the IEC will publish the standard as IEC.

All devices in a wireless subnet communicate at a pre-arranged time and pre-selected frequency using time division multiple access, with the length of a time slot being ______.

Just as DCSs and PLC-based systems have become the predominant automation technologies for plant automation since the 1980s, SCADA systems have been the predominant automation technology for geographically dispersed processes since the ______.

SCADA systems generally consist of a central computer system and geographically-dispersed remote terminal units that are connected via some form of wide-area telecommunications technology. SCADA systems are used to monitor and control processes, such as liquid and gas pipelines, electric power transmission and distribution, water and sewage systems, and ______ systems.

SCADA systems replaced the older telemetry technologies that were used for these applications prior to the invention of reasonably priced computer systems. The invention of 16-bit minicomputers in the ______ spurred the development of SCADA, and the continued evolution of computers and increases in computing power allowed SCADA vendors to continue to add more features, functions, and applications to their products.

The most basic form of RTU protocol is one that performs master-slave polling, wherein the SCADA host sends data requests to RTUs and the RTUs respond with the requested data. A protocol that exemplifies this concept is Modbus RTU, which was originally developed by Modicon, a major PLC manufacturer, for communicating with their PLCs, yet it has been extensively used for other purposes and with other devices. The basic frame structure of Modbus RTU protocol was shown in figure ______.

Most ModbusRT messages tend to be reasonably short, but a massive data request could generate a long response message —due to the 2-byte message length field, a response could be as big as ______.

With a device that communicates using Modbus protocol, it is necessary to obtain vendor documentation that defines the function codes supported by the device, as well as a mapping of data-to-register addresses, so that the host driver software can be configured ______.

Modbus is probably the best example of a simple, low-overhead RTU protocol. At the other end of the spectrum is the Distributed Network Protocol, originally developed by Westronic, Inc. for the U.S. ______.

In FOUNDATION Fieldbus, the fieldbus Data Link layer is divided into two sublayers: Fieldbus Media Access Control and Fieldbus Data Link Control. For access control, FOUNDATION Fieldbus modifies the token-passing bus arrangement of rotating the token and, instead, opts to use a method similar to the Data Highway Plus floating bus master. Here, the master is called a Link Active Scheduler and uses two different tokens, specifically the delegate token and the reply token. The delegate token is used for ______ and the reply token is used for acknowledging the delegate token.

In FOUNDATION Fieldbus, background processes are acyclic messages and use a form of the client-server model. For the cyclic processes, FOUNDATION Fieldbus uses a publisher-subscriber model. The main difference between the two models is that publisher-subscriber normally requires the subscriber to subscribe to a certain event controlled or reported by the publisher, then any time the event occurs, the publisher sends notifications to all those that subscribed. FOUNDATION Fieldbus builds applications using ______.

In FOUNDATION Fieldbus, the User layer sees the nodes as virtual field devices, which are the interfaces between the communications protocol and the function block. System management is concerned with the following five issues: Device Tag Assignment, Clock Synchronization, and Scheduling of Application Processes. The H1 fieldbus is intended to connect to ______.

In FOUNDATION Fieldbus, the User layer sees the nodes as virtual field devices, which are the interfaces between the communications protocol and the function block. System management is concerned with the following five issues: Device Tag Assignment, Clock Synchronization, and Scheduling of Application Processes. Clocks are synchronized from a master clock, so all devices maintain the same real time. Scheduling is required to ensure there is neither dead time while waiting for execution, nor variance in timing ______.

The H1 fieldbus is intended to connect to ______.

The higher-speed mode FOUNDATION Fieldbus for High Speed Ethernet is intended for intersegment or internetwork connectivity, however it may also contain devices other than those intended for interconnectivity such as measurement or control devices. The Fieldbus Foundation, a nonprofit, vendorsupported organization, tests protocol stacks and devices to ensure that they conform to the ______.

The advantages of FOUNDATION Fieldbus are as follows: It is designed for process control. It has an open system standard. Compared to conventional devices, a FOUNDATION Fieldbus device has: High information flow. It provides good ______ performance.

The advantages of FOUNDATION Fieldbus are as follows: It is designed for process control. It has an open system standard. Compared to conventional devices, a FOUNDATION Fieldbus device has: ______ information flow.

In FOUNDATION Fieldbus, the fieldbus Data Link layer is divided into two sublayers: Fieldbus Media Access Control and Fieldbus Data Link Control. For access control, FOUNDATION Fieldbus modifies the token-passing bus arrangement of rotating the token and, instead, opts to use a method similar to the Data Highway Plus floating bus master. The data is placed on the wire using ______ encoding.

In FOUNDATION Fieldbus, the fieldbus Data Link layer is divided into two sublayers: Fieldbus Media Access Control and Fieldbus Data Link Control. For access control, FOUNDATION Fieldbus modifies the token-passing bus arrangement of rotating the token and, instead, opts to use a method similar to the Data Highway Plus floating bus master. The data is a valid Manchester-coded signal; the preamble and start/stop delimiters are “nonvalid” signals and are easily discerned from the data ______.

In FOUNDATION Fieldbus, the fieldbus Data Link layer is divided into two sublayers: Fieldbus Media Access Control and Fieldbus Data Link Control. For access control, FOUNDATION Fieldbus modifies the token-passing bus arrangement of rotating the token and, instead, opts to use a method similar to the Data Highway Plus floating bus master. As specified in IEEE 802.2, the fieldbus Data Link layer, is divided into two sublayers: Fieldbus Media Access Control and Fieldbus Data Link Control. For access control, FOUNDATION Fieldbus modifies the token-passing bus arrangement of rotating the token and, instead, opts to use a method similar to the Data Highway Plus floating bus master. The failure of any communications element cannot interfere with other transactions for more than 1 ______.

In FOUNDATION Fieldbus, the fieldbus Data Link layer is divided into two sublayers: Fieldbus Media Access Control and Fieldbus Data Link Control. For access control, FOUNDATION Fieldbus modifies the token-passing bus arrangement of rotating the token and, instead, opts to use a method similar to the Data Highway Plus floating bus master. The SP50 standard specifies up to 12 bus-powered devices in non-intrinsically safe segments. The failure of any communications element cannot interfere with other transactions for more than 1 ______.

DNP3 is a non-proprietary protocol standard that is available for use by any manufacturer or vendor. Unlike Modbus, which only deals with 16-bit integer values and discrete bits, DNP3 supports several data types, such as floating point and integer values, as well as multi-bit status indicators and counters. DNP3 supports RTU configuration downloading and can support conventional polling, reporting of changes since prior poll, and unsolicited report-by-exception. DNP3 supports several ______ types.

The early RTUs had to contend with poor quality communication channels that could suffer from environmental factors and be subject to noise and interference. For that reason, RTU protocols included check codes to permit the identification of bad messages. This approach was primarily used when RTUs were dumb, in order to put a human operator in the loop as the intelligence that kept a bad or broken message from operating field devices. With the arrival of smart RTUs and much more reliable communication error detection and correction techniques, SC-O protocols became less of a requirement and more of a legacy/backwards-compatibility issue—but note that DNP3 supports an S-C-O sequence. The early RTUs had to contend with poor quality communication channels that could suffer from environmental factors and be subject to noise and interference. For that reason, RTU protocols included check codes to permit the identification of bad ______.

Because the communication systems available for SCADA use could have momentary disruptions or even long-duration outages, the SCADA system protocol software usually supported timeout and retry logic. Most systems allowed for some number of retries after which they would skip on to the next RTU in the polling sequence. This often resulted in setting various flags or indicators to both alert personnel of the problem and to allow the driver to either remove the RTU from polling or place the RTU on a separate periodic test-poll list. Because the communication systems available for SCADA use could have momentary disruptions or even long-duration outages, the SCADA system protocol software usually supported timeout and ______ logic.

In the electric utility market, RTUs have become one means for extracting and consolidating all the information from the other numerous intelligent electrical devices in a substation. An IED has local control intelligence, performs electrical protection functions, has the ability to monitor processes, and communicates directly to a SCADA system. The RTU in such applications provides a virtual RTU to each host and hides the details of the IED communications. In the electric utility market, RTUs have become one means for extracting and consolidating all the information from the other numerous intelligent electrical devices in a substation. An IED has local control intelligence, performs electrical protection functions, has the ability to monitor processes, and communicates directly to a ______ system.

None of the RTU protocols traditionally developed for SCADA use included any security mechanisms. In recent years, there has been a growing concern about the possibility of malicious manipulation of SCADA systems. Another problem is that many of these devices introduce a time delay as they perform message encryption and decryption that often leads to timeout faults at the host and/or RTU, causing the channel to be declared as failed. None of the RTU protocols traditionally developed for SCADA use included any ______ mechanisms.

By the early 2000s, the computing power of RTUs reached the point where it was possible to implement both Ethernet and TCP/IP networking hardware and software in an RTU. Some RTU manufacturers even began running embedded versions of commercial operating systems, such as Windows and Linux, in their products. This allowed the use of well-known software applications and IP-based IT protocols, such as: telnet, http, and ftp; IP-based SCADA protocols, such as the Inter-Control Center Protocol and the utility communications architecture; some protocols from the European IEC 61850/IEC 60870 standards for substation automation; IED communications; and SCADA. By the early 2000s, the computing power of RTUs reached the point where it was possible to implement both Ethernet and TCP/IP networking hardware and software in an RTU. Some RTU manufacturers even began running embedded versions of commercial operating systems, such as Windows and Linux, in their products. This allowed the use of well-known software applications and IP-based IT protocols, such as: telnet, http, and ftp; IP-based SCADA protocols, such as the Inter-Control Center Protocol and the utility communications architecture; some protocols from the European IEC 61850/IEC 60870 standards for substation automation; IED communications; and ______.