Understanding Smart Sensors - Nomads.usp

182 Understanding Smart SensorsVAV 1 VAV 2 VAV 3 VAV 4DiffuserBuildingmanagementsystemReceivertranslator1 2 3WZS WZS WZS4WZSWirelesszonesensorSetup tool Zone 1 Zone 2Figure 8.4 Wireless zone sensing.Wireless data loggers are being used in clean rooms to pinpoint localizedhumidity fluctuations [10]. In this wireless sensor application, the measurementis required only to locate the source of a problem. Flexibility in choosingthe test sites, as well as avoiding clean room suits and drilling holes through thewall, was paramount to design considerations. Again, the low interference possibleusing spread spectrum technology has provided the wireless transmissionof real-time data in an environment that previously prohibited radio transmission.Up to 20 data loggers have been linked to a single wireless base station. Asa result, a single PC can handle the measurements from a number of widelyseparated data collecting units.8.2.4 Optical Signal TransmissionThe infrared spectrum is also used for transmitting data. It is low cost for costsensitiveapplications and does not require licensing. However, it is limited toline-of-sight (LOS) transmission and cannot penetrate solid objects. The infraredspectrum (indicated in Table 8.1) is from 0.7m to 0.1 cm.