Transmissibility of 802.15.1 - Compliant Radio in Machining Enclosures in Industrial Environments

Wireless sensors used in plant floor environments have been studied for obstruction and multipath propagation effects on signal quality. The trend towards wireless industrial data networks motivates this study, which explores the use of IEEE 802.15.1 radios in a machine shop at varying levels of operation. Previous studies have investigated the use of a wireless sensor embedded in a rotating tool holder to monitor tool life. In order to obtain information furthering the potential use of low power radio in conjunction with machining enclosures, a Bluegiga WT12 Class 2 Bluetooth 2.1 module is placed within several CNC machining enclosures at varying table positions and heights. An exterior module receives the data from the enclosed unit, and the module’s position is also varied in 3 dimensional space. Bit Error Rate and Received Signal Strength are measured, and the effects of spatial obstruction and multipath propagation are analyzed. An Agilent 8563E spectrum analyzer equipped with an Aaronia HyperLOG 7060 EMC antenna is also used to repeat the measurements at all of the points in order to provide EMI channel characterization and a redundant source of signal power data for comparison. Large-area transmissibility testing indicates that received signal strength is not dependent upon equipment operation. The enclosure tests (perimeter, height, and proximity comparison) suggest that distance, both static and transient path obstructions, multipath propagation, and line-of-sight are factors that influence bit error rate and received signal strength. Spectrum analyzer measurements in our shop show no significant emissions in the 2.4 GHz range that cause interference. At no time during this study did the bit error rate reach 0.2% of the transmitted bits and there were no failures in transmitting text between modules. Overall, the findings indicate that reliable data transmission with low power off-the-shelf Bluetooth modules is feasible.