Industrial Wireless Sensor Networks

Monitoring, Control and Automation

R Budampati, S Kolavennu

• Publisher: Woodhead Publishing
• Year: 2015
• Print ISBN: 9781782422303
• eBook ISBN: 9781782422372
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Industrial Wireless Sensor Networks: Monitoring, Control and Automation explores the explosive growth that has occurred in the use of wireless sensor networks in a variety of applications during the last few years. As wireless technology can reduce costs, increase productivity, and ease maintenance, the book looks at the progress in standardization efforts regarding reliability, security, performance, power consumption, and integration. Early sections of the book discuss issues such as media access control (MAC), antenna design and site survey, energy harvesting, and explosion-proof design. Subsequent sections present WSN standards, including ISA100, ZigBee™, Wifi™, WirelessHART™ and 6loWPAN, and the applications of WSNs in the oil and gas, chemical, food, and nuclear power industries. - Reviews technologies and standards for industrial wireless sensor networks - Considers particular applications for the technology and their ability to reduce costs, increase productivity, and ease maintenance - Focuses on industry needs and standardization efforts regarding reliability, security, performance, power consumption, and integration.

Part One

Wireless sensor network technologies and standards

1

Industrial data communications protocols and application layers

D. Caro CMC Associates, Arlington, MA, USA

Abstract

Industrial data communications began with wired networks. Many different protocols, each developed for a specific purpose and application, have been commercialized. Some of these have been included in the IEC Fieldbus standard (IEC 61158) while others have not. The differences between process control, factory automation, and hybrid networks are described. While this chapter reviews most of the popular protocols, it cannot cover all of the lesser-used or more obscure networks. Additionally, a brief introduction to the two wireless network protocols that have been developed for process control applications is included. Note that security is not provided for any of the wired industrial automation protocols.

Keywords

Fieldbus

Ethernet

Process control

Fluid process industries

Factory automation

Discrete parts manufacture

SCADA

Hybrid/batch

1.1 Data communications in manufacturing

It is generally acknowledged that data communications in the process control segment of manufacturing began in 1976 with the introduction of the “Data Hiway” as the data communications element of the Honeywell TDC-2000, the first commercial distributed control system (DCS). Prior to that introduction, data transfer between units of manufacturing automation systems either did not exist or were proprietary point-to-point serial and parallel wired data links.

1.1.1 Market segmentation

The industrial automation market is segmented by the type of product being manufactured. The following sections describe this segmentation by product.

1.1.1.1 Fluid process industries

Products being manufactured are generally classified as flowing fluids, gases, powders, or solids formed into sheets. Characteristic is that the product being produced is totally contained within the manufacturing equipment and is generally not visible to the humans engaged in supervising its production. The only exception to this are the sheet-formed products that are visible, but are contained by the manufacturing machinery while being processed. Industries in this market segment include: oil and gas, petroleum refining, petrochemicals, fine chemicals, heavy chemicals, cement, glass, plastics and polymers, cement, lime, iron and steel, alumina and aluminum, pulp and paper, and sheet plastics. Products are generally produced by chemical reaction of raw materials or the physical separation of the contents of a raw material by some process such as distillation, filtration, etc.

Automation of continuous manufacturing processes depends upon the synchronous acquisition of data, computation of a manipulated variable, and monitoring for abnormal conditions on a continuous basis in order to hold the process at a steady state. The feedback control computations may be done in ruggedized process controllers or may be distributed to field instruments themselves when equipped with the appropriate communications network. Information on the performance of the process control system is reported to human process operators via the HMI (Human Machine Interface).

1.1.1.2 Discrete parts manufacture

Products in this segment are generally identified as discrete parts manufactured from basic components that themselves may be produced by factories. The most frequent examples are the automotive manufacturing industries producing automobiles, trucks, and buses, plus their components such as engines, wheels, tires, and their respective parts as well. Products are produced by some combination of casting, cutting, drilling, machining, fastening, and assembly of component parts.

Automation of discrete manufacturing processes is usually accomplished through a series of logical and sequential operations using discrete data from distributed sensors, control actions determined by programmable logic controllers, and actions performed by outputs to motors, solenoid valves, and other switched electrically powered devices. Often, the state of the manufacturing control system is reported to human operators via an HMI.

1.1.1.3 Hybrid/batch

Most of the bulk chemical, petroleum, paper, and metals processes are continuous manufacturing in which raw materials are fed at one end, and products are produced continuously. Many specialty products are manufactured in small lots called batches. Automation of batch processes frequently involves opening and closing valves, turning electric motors on and off, and changing the mode, setpoint, and often the tuning of feedback control loops. Since the process itself involves many steps to completion, the batch automation system must also move the process from one state to another, as well as holding the process at constant conditions within each state. The HMI for batch process automation usually allows the process operator to participate interactively with process operation.

1.1.1.4 Supervisory Control and Data Acquisition

Supervisory Control and Data Acquisition (SCADA) systems were developed to allow operators to “supervise” the operation of pipelines, tank farms, water and waste treatment, and electric power distribution networks, where the respective pumps or compressors, tanks, and substations are located at a substantial distance from the operator. The major elements of a SCADA system are the remote termination unit (RTU) that converts local sensor and actuator data to digital values and is located at a distance from the operator, the master station where the operator and an HMI are located, and a wired or wireless communications network to join the two.

The “Control” part of SCADA is operator manual operation of remote devices such as pump and compressor motors, instrumentation or other remote control loops, opening or closing valves, and the selection of switch settings for substations. In all cases, the system validates the present status of the device being operated, reports it on the SCADA HMI, and allows the operator to check that status before operating it (check before operate).

1.1.2 ISO/IEC 7498-1 seven-layer Open System Interconnection (OSI) model

In 1984, the ISO finally approved a seven-layer model for data communications. The palindromic name for this model is the ISO/OSI stack. This model divides all communications into seven distinct layers, as outlined in Table 1.1.

Table 1.1

ISO/OSI seven-layer interconnection model

Layer number	Name
7	Application
6	Presentation
5	Session
4	Transport
3	Network
2	Data Link
1	Physical

The ISO/OSI model was initially useful in describing the intricacies of the digital telephone network, but was found to be too complex for the Internet, which uses only five layers for its model (it does not have layers 5 and 6). Likewise, many industrial automation digital networks do not implement all of the layers as distinct entities, but distribute the missing layer functions to adjacent layers, or do not implement those missing layers. For example, the Foundation Fieldbus H1 network protocol uses only layers 1, 2, and 7; the functions of the Network, Transport, and Session Layers are provided by the Data Link Layer, and the functions of the Presentation Layer, if any, are provided by the Application Layer or within the application itself.

Notice that there is no layer defined for security. For wired networks, security was considered an after-thought, not part of the network protocol. The thought process was that intrusion or network access always required a physical connection that was usually not possible without physical access or attachment. Until Internet connections became possible, the flaw in this logic was not revealed. Once a network can connect to the Internet, all security options to control access, authorize users, and prevent intrusion become necessary. The unfortunate result is that there are no standards for security with most wired networks, and it becomes a vendor or user problem.

1.2 Physical and Data Link Layers

Most of the industrial networks are based upon standard network protocols used for other purposes, but a few of them have unique properties that are defined in the lowest layers in order to provide the special features needed for the particular industrial area for which they were created.

1.2.1 Analog 4–20 mA

For many y...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of contributors
• Woodhead Publishing Series in Electronic and Optical Materials
• Part One: Wireless sensor network technologies and standards
• Part Two: Wireless sensor network applications
• Index