On-line diagnostics in the Mobile Spatial coordinate Measuring System (MScMS)

Mobile Spatial coordinate Measuring System (MScMS) is a wireless-sensor-network based systemdeveloped at the industrial metrology and quality engineering laboratory of DISPEA – Politecnico di Torino. It has been designed to perform simple and rapid indoor dimensional measurements of large-size volumes (large-scale metrology). It is made up of three basic parts: a “constellation” of wireless devices (Crickets), a mobile probe, and a PC to store and elaborate data. Crickets and mobile probe utilize ultrasound (US) transceivers in order to evaluate mutual distances. The system makes it possible to calculate the position – in terms of spatial coordinates – of the object points “touched” by the probe. Acquired data are then available for different types of elaboration (determination of distances, curves or surfaces of measured objects). In order to protect the system against causes of error such as, for example, US signal diffraction and reflection, external uncontrolled US sources (key jingling, neon blinking, etc.), or software non-acceptable solutions, MScMS implements some statistical tests for on-line diagnostics. Three of them are deeply analyzed in this paper: “energy model-based diagnostics”, “distance model-based diagnostics”, and “sensor physical diagnostics”. For each measurement, if all these tests are satisfied at once, the measured result may be considered acceptable with a specific confidence coefficient. Otherwise, the measurement is rejected. After a general description of the MScMS, the paper focuses on the description of these three online diagnostic tools. Some preliminary results achieved by the system prototype are also presented and discussed.