Understanding Smart Sensors - Nomads.usp

Transceivers, Transponders, and Telemetry 181Frequency-shiftkeyingmodemRadio/phonedriversX.25error-correctingprotocolFirmware kernelApplicationprogramlayerTerminaldriversFigure 8.3 Wireless data using a PC card.to-zero inverted (NRZI) bit patterning increases the clock-recovery data for thereceiver. Data is transmitted in packets of up to seven adjustable-length frames.A compression algorithm built into the firmware kernel allows data compression,transfer, and analysis prior to transmission. Error correction capability isachieved by allowing the receiver to store ahead frames that are received out ofsequence and to request retransmission of any missing frames.A file-level protocol facilitates the exchange of data between the mobileunit and the base unit. A microprocessor controls the data transmission andservices the serial ports and the parallel port. Global positioning system(GPS) data (discussed in Section 8.3.3), mobile data terminals, and bar codereaders/scanners are among the immediate applications for such RF datatransmission.8.2.3 Wireless Zone SensingWireless zone sensors (WZS) have been developed for buildings using thespread spectrum technique. The wireless sensors are part of the modern buildingautomation systems designed for energy efficiency and precise control ofmany individual areas [9]. Figure 8.4 demonstrates a typical system with wirelesszone sensors.The WZS is a spread spectrum transmitter that provides room temperatureand other status information to a receiver located up to 1,000 ft away. Atranslator in the unit converts the wireless data to a wired communication link.The wired communication link distributes data to variable air volume (VAV)terminal controllers and to the building management system. The VAV adjuststhe valve opening to allow more or less flow to the area as required by the WZS.A sensor is matched to its associated VAV by a setup tool connected to eachWZS during the installation process. The lithium-battery-powered WZSsare designed to operate an average of two years before the batteries need to bechanged.