Why Wireless I/O?
Many companies have geographically scattered assets, so they need sensor data at a central point. In the past, the only available option included digging trenches or running conduit and pulling wire to acquire the signals. Today, many wireless I/O applications offer simple, cost-effective measurement of monitoring points to eliminate manually collecting field data, thereby improving labor productivity.
In more sophisticated applications, wireless I/O enables users to extract full diagnostic data and predictive intel-ligence from the devices that will automatically notify the appropriate personnel of the precise problem before a costly asset, unit or plant shutdown occurs.

Foundation of Wireless I/O and I/O Expansion
The foundation of wireless I/O and I/O expansion is license-free 900MHz spread spectrum radio technology designed specifically for integration into remote assets and SCADA systems. This technology has been used reliably in field automation for almost 20 years.
Frequency Hopping Spread Spectrum (FHSS) uses pseudo-random hopping patterns that are proprietary to the radio manufacturer, making industrial FHSS radios inherently secure and less prone to interference. This makes FHSS the preferable choice for industrial wireless I/O applications, such as simple analog and digital signals.

Advantages Compared to Wired Options:
In addition to the labor and material costs associated with hard-wiring instrumentation, one of the other advantages is deployment speed. Wired systems can take days or weeks to be installed, isolated and commis-sioned. Wireless I/O networks generally require only the end points to be installed an`d configured, saving substantial time for projects with aggressive schedules.
In the event of a communication failure, communi-cation link alarms let the user know if a loss of signal between an I/O slave and the I/O master is halting data transfer from the instrument. The I/O slave will control its outputs based on the fail-safe default condition that was pre-programmed in the radio during system configuration.

Wireless I/O Expansion
Scalability is the next biggest advantage of wireless I/O compared to hard-wired alternatives. Some I/O expansion solutions allow users to expand their wireless I/O capabil-ity by adding expansion modules.
Each expansion module allows for 12 additional I/O points. Up to 15 modules can be stacked and snapped onto a base radio module. This allows for a scalable solution of up to 192 I/O points per remote location via Modbus from the master radio into the PLC. Each I/O slave is given a unique Modbus device ID, and the PLC is configured to poll Modbus registers of the specific Mod-bus address for each slave device.

Wired I/O Expansion
While the I/O expansion module offers great utility when stacked on a radio module, it also can be deployed without a radio on an I/O expansion base module. This is useful for applications in which the PLC has limited I/O capacity.
The expansion stack starts with a PC module directly connected to the PLC via the serial port. It’s Modbus addressable, as is the radio module. Users can add more I/O expansion modules to meet the I/O count required for the application. This offers a cost-effective, scalable solution for bringing in additional I/O points to the controller system with minimal programming and setup.

Reliability
Wireless systems must be just as reliable as traditional copper wire. Corrupted data can result in anything from a disruptive glitch to a devastating failure.
To identify and ultimately maximize signal reliability, users should perform a radio-frequency (RF) site survey or path study. Also, use a comprehensive software package that will allow for system configuration and diagnostic monitoring of signal reliability