A wireless reference node to provide self-calibration capability to wireless sensors networks

Wireless sensors networks (WSNs) are constantly expanding their application field, from simple two-state measurements (e.g., on/off, proximity detection, etc.) to distributed many-parameter measurements. Commercial WSNs offer a wide range of functions and performance with sensors sometimes achieving accuracy comparable with desktop instrumentation. However, the advantage of using such sensors for in-situ monitoring is often offset by the need of partially dismantling the network at the time of periodic network nodes calibration. As a result, new reference standards suitable for automatic and in-situ calibration of such sensors networks are needed in order to reduce the calibration cost, the inherent inefficiency and the logistic problems of a laboratory calibration, further exploiting the communication capabilities of a WSN. This work discusses the development of a wireless reference node (WRN) for the measuring of environment quantity such as air temperature (T) and relative humidity (RH). The module was developed for accurate measurements of additional environmentrelated quantities whose principle is based on a capacitive sensing mechanism (e.g. pressure, air-flow, moisture, etc…). The WRN performance was investigated in the temperature range from 0 °C to 40 °C and in the relative humidity range from 10 %rh to about 90 %rh for its potential use as a transfer standard for automatic in-situ calibrations. Some of novelties here reported were patented and are now available to upgrade a basic WSN with an automatic in-situ calibration capability.