Stretching Wireless IO Throughout Your Infrastructure
Brent E. McAdams, Director, Major Accounts & Product Management
FreeWave Technologies, Inc.

Introduction
Tough economic times are upon us, and as automation budgets remain flat or decline, doing more as efficiently as possible with existing assets and infrastructure has never been more important. Wireless IO offers one such avenue to accomplish this objective. Without question, the use of wireless IO offers substantial and measureable cost savings in terms of engineering, installation and logistics as well as dramatic improvements in the frequency, currency and reliability of field data collection. As a result, companies can realize incremental production results and efficient use of each expense dollar with the emergence of this wireless field infrastructure. By having dependable access to timely information, companies can establish and maintain excellent situational awareness of their operations.

Many wireless IO applications offer simple, cost-effective measurement of monitoring points to eliminate manual collection of field data, thereby improving labor productivity. Alternatively, in more sophisticated applications with a central processing device, wireless IO enables users to extract full diagnostic data allowing for predictive intelligence from these devices which then will automatically notify the appropriate personnel of the precise problem before a costly asset, unit or plant shutdown occurs.

Objectives
Faced with internal pressures to cut costs and optimize operations, corporate managers and automation professionals are looking at wireless IO as integral part of a converged network to achieve benefits, such as greater visibility, better data integration, reduced costs and simplified management.

Through deployment of Wireless IO, many companies are discovering that networked wireless assets and uniform communications of industrial systems are the keys to optimized operations and a lower total cost of ownership (TCO). In addition, they are starting to embrace the technology for industrial automation and control environments.

With the prospect of being able to solve virtually any remote monitoring or control application, many people throughout the industry are viewing wireless IO as an exciting innovation for addressing issues previously deemed cost prohibitive, not technically feasible, or lacking in sufficient reliability. This excitement is well-justified with the expectation that having additional knowledge about the operation will lead to a safer and more profitable enterprise.

Overview
In general, wireless has traditionally been thought of as a way to send signals over distances greater than a mile. However, it also provides advantages in short-distance applications, especially in applications in which IO data must be transmitted several hundred feet and running cable and conduit is challenging. Many users must overcome hazards and obstructions. The result is that companies buy and install more cable than they would need to go around them, not to mention the permitting and costly downtime. Further, depending on the area classification, companies also may need to recertify the environment after each new cable installation and if these cables are damaged, the costly cycle begins again.

The basis for wireless IO is frequency hopping spread spectrum (FHSS) technology. FHSS helps transceivers successfully deliver IO despite competing signals from other devices. FHSS varies the carrier frequency throughout the spectrum in a pattern recognized solely by the transceivers assigned to communicate with one another in the network. This technology is particularly well-suited for sending small packets of information, such as IO in a noisy, high interference environment. Devices also can be equipped with external antennas, allowing radios to be mounted within a few feet of an obstruction but sending and receiving signals via antennas above the obstructions or interference.

Wireless IO Integrated in Base Network
In the following diagram (below), wireless IO is integrated into the base wireless network architecture. Regardless of where the information is needed, field IO points are accessible throughout the network. One of the key drivers associated with deploying wireless technologies is economies of scale. In other words, once the base network is built out, deploying an additional point is incremental, thus creating a “pay- as-you-go” architecture. Deploying wireless IO illustrates this concept nicely and results in a much lower total cost of ownership.
The network depicted in the referenced diagram integrates two types of wireless IO. The first is wire replacement. As the name implies, the RF technology used essentially replaces the wire that would be used to hardwire the assets. In this scenario, the wireless IO master (identified as #6 in the diagram) functions as a point-to-multipoint slave in the base serial network while, at the same time, functioning as a master to the wireless IO slaves (identified as #9 in the diagram).

From a functionality perspective, the wireless IO master offers a serial (RS-232, RS-485, RS-422) data port as well as a terminal strip for the individual analog and digital IO points. The analog and digital IO points are transmitted wirelessly from the IO slave back to the IO master and hardwired to the remote terminal unit (RTU) or programmable logic controller (PLC). The IO master then splits its duty cycle between a slave to the serial network and a master to the IO network, allowing multiple uses from existing infrastructure.

The second type of wireless IO is Modbus. In Modbus wireless IO, the same IO slaves are used, but the master radio becomes just a serial radio, connected to the RTU, PLC or SCADA host through a serial port, thus eliminating the need for hardwiring points on the master. A maximum of 256 IO slaves (with a full complement of IO) can be integrated into the network using 8 bit Modbus addressing while an overwhelming 65,535 IO slaves can be integrated into the network with 16 bit Modbus addressing.

Network Diagram Legend
1) Ethernet Backbone Gateway – Connected directly to the IP backbone or SCADA server and offers greater throughput than serial radios and allows multiple networks to be polled at once.
2) Ethernet Backbone Endpoints – Wirelessly linked up to 15 miles line of sight (LOS) and offers a built-in two (2) port terminal server to connect multiple serial masters or one master with diagnostics (as shown). Ethernet port may be used for applications such as an IP based security camera.
3) Serial Master – Connected to one of the serial ports on the Ethernet endpoint. Diagnostics, which is available via a second port on the radio, may be tied into the second serial port of the Ethernet Endpoint. This radio offers a robust link of up to 60 miles (LOS).
4) Modbus Master – Same radio as #3 but configured as a Modbus master.
5) Serial Point to Multipoint Slave – Connected serially to the RTU or PLC.
6) IO Master Configured as a Point to Multipoint Slave – As mentioned above, the data port is connected serially to the RTU or PLC. In addition, the analog and digital points are landed from the IO terminal block directly to the RTU or PLC. This single radio solution allows the SCADA server to poll the RTU or PLC while it is splitting its duty as a master to the IO slaves. A great example of leveraging existing infrastructure investments.
7) Modbus IO Slave – This radio is configured as a point-to-multipoint slave and assigned a Modbus address. The data port is active as well. Therefore, when the SCADA server polls the RTU or PLC, it will poll the Modbus address assigned to either device. However, if the SCADA server is polling specific IO associated with the radio, it will poll the Modbus ID assigned to the radio, along with the appropriate register(s), i.e. register 30001 for AI1.
8) Serial Point to Multipoint Repeater – This is a serial radio configured as a repeater with “Slave/Repeater” functionality enabled. Not only will the radio act as a slave and pass Modbus data through the data port, it also will repeat the signal to other Modbus IO slaves (represented by #12) This functionality allows companies to truly take advantage of existing infrastructure investments to bring back additional field IO points.
9) IO Slave – This radio is a wire replacement IO slave. Associated instrumentation is landed directly to the terminal block of the radio (i.e., analog inputs, digital inputs, digital outputs, etc.). The IO is mapped to the wireless IO master.
10) IO Slave – This radio is a modbus IO slave. Associated instrumentation is landed identical to #9 above. However, no mapping is required, functions the same as #7 above.

Expandability
In the above examples, limitations exist with both the wire replacement and Modbus wireless IO solutions. In wire replacement, it is the capacity of the physical terminal block on the wireless IO master. There only are so many points that can be landed to the IO master, thus inherently minimizing the number of IO slaves that connect to a single IO master. In the Modbus solution, the master limitation disappears as now there is a serial connection to the RTU, PLC or polling host allowing more than 65,000 Modbus IO slaves, with a full complement of IO, that connects to a Modbus master. While impressive, in this scenario, the limitation is the IO slave as there are only so many devices can be hardwired to the radio. Enter wireless IO expansion.

The image (right) illustrates the ability to stack expansion modules onto an existing wireless IO slave, thus dramatically increasing the IO count. Where the base IO slave only may have a complement of two analog inputs (AI), two analog outputs (AO), two digital inputs (DI) and two digital outputs (DO), a single expansion module will increase that compliment dramatically and offer the user the ability to customize the IO module for a given installation.

For instance, a single expansion module will offer an additional four AIs, two Isolated DIs, two DOs and allow the user to configure four more universal terminals in any combination of I/O such as AIs, AOs, DIs or DOs. A single module provides up to 12 additional IO points. Depending on the manufacturer offering expansion I/O, up to 64 modules can be stacked on a single radio guaranteeing the necessary I/O count for any installation. Expandable IO is yet another avenue for stretching your wireless IO throughout your infrastructure. The image (right) illustrates how expansion I/O can be implemented. Each stack is Modbus addressable and as mention above, offers 256 stacks with 8 bit Modbus addressing and over 65,000 with 16 bit addressing. The stack also offers a data port that can be connected to an RTU or PLC.

While the I/O Expansion Module offers great utility when stacked on a radio module, some manufacturers allow the module to be deployed without a radio. This is very useful in applications where an RTU or PLC has limited IO capacity. The expansion module is Modbus addressable and is connected serially through an available communications port on the RTU/PLC. As when stacked on a radio module, additional I/O expansion modules are added to meet the I/O count required for the application.

Summary
The adoption of Wireless I/O and the flexibility it offers represents one of the simplest and most straightforward ways to stretch your wireless Infrastructure investment. Wireless I/O technologies are affordable, secure, and can be implemented non-intrusively, without disrupting existing operational processes. In this highly competitive and dynamic business climate, this is not just technology for its own sake; companies are recognizing the power and potential of what it truly provides.

The cliché says that “only the strong survive”. However, in every down economy, there are opportunities to excel while others stand still. Companies that make the most of existing infrastructure investments in this business climate, while at the same time increasing their asset utilization will be more resilient and better-positioned for success when the economy rebounds. Wireless IO provides improved leverage of existing infrastructure, allows for better resource optimization and gains relief from the current budget crunch in order to build a strong foundation for future growth.

About the Author
McAdams is the director of major accounts and product management at FreeWave Technologies, Inc. Prior to joining FreeWave, McAdams served as the Vice President of Technology and Business Development for the US Telemetry Corp. where he led product development strategy and business development initiatives. Additionally, McAdams spent more than 10 years as a contract electrical and instrumentation engineer with Exxon Chemical in Baton Rouge, LA.

FreeWave Technologies manufactures reliable, high performing, low power consumption, spread spectrum and licensed radios for mission-critical data transmission. Based in Boulder, Colo., FreeWave designs and manufactures radios for oil and gas, utility, military and numerous other industrial applications. For additional information, contact FreeWave directly 866-676-4046 or at www.freewave.com.

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