A plurality of sensor units are distributed over an area and communicate via a network with a central monitoring unit. The sensor units include sensor arrays that provide them with raw data in response to the presence of selected compounds in the ambient fluid. The raw sensor data is then processed...http://www.google.com.hk/patents/US5832411?utm_source=gb-gplus-share專利 US5832411 - Automated network of sensor units for real-time monitoring of compounds in a fluid over a distributed area 
