Wireless sensor networks
H&S, in the past ten years, has been active in providing application and networking solution to cryogenic banks and hospitals. In medical diagnostic environment, sensors measurements are centralized through long course, because of this there is a relevant drop in network flexibility.
The presence of different links types and the agreement of builders for several standards increases the need of wirings, requiring bus both similar and adherent to different standards in the same environment. It is necessary to consider also that realizing wirings in addition to existent systems in medical operative or sterile environments, is a great problem, that makes impossible to add sensors in an environment of the same sort.
The installation cost and the possibility of extending the network in future, are two weak points of sensor cable networks; in addiction there is a third great problem towards practicality of the cable systems around patient, making the operative space difficult and less accessible for doctors and attendants.
For several reasons, wireless sensor systems are preferable to cable system in several situations, particularly in medical and hospital environment.
ZigBee protocol defined in the IEEE 802.15.4 protocol, describes the physical PHY level and the MAC underlevel of the ISO-OSI stack.
ZigBee peculiarity is to fully realized necessities of sensor network both for knots powered by network and knots powered by battery. The coordinator knot of network is typically powered by network and it is always active.
Other knots remain in a low consumption state until when there is necessity of data transmission. If the data amount is limited, it is possible to maintain the knot in a low state of consumption for long time. The periodical transmission of little amount of data is a typical characteristic for a sensor network.
Another characteristic of ZigBee protocol, that makes it particularly suitable for an employ in sensor networks, is the possibility of “hooking” network and transmitting in short times, more inferior than the other wireless protocols, known until today.
H&S has been developing a complete solution based in the ZigBee standard, including coordinators and “End device” knots that cooperate in realizing a wireless network of powered and/or autonomous sensors. The coordinator modules offer a standard interface Modbus, through which it is possible to collect data that are concentrated in the coordinator and make them available for a superior level, PLC o PC Supervisor with a SCADA on board for example. The coordinator knots can be reached by bus 485 by serial line or by ethernet.
The availability of a standard interface like Modbus allows also the integration of the wireless solution inside pre-existent and also wired solutions.