Motion Sensor Time Correction for Accurate Occupancy Tracking
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Solution Overview
Problem
Building management systems face challenges in accurately determining occupancy due to misaligned time clocks in motion sensors, leading to insufficient precision in timing data, which existing solutions address at increased cost or with insufficient precision.
Innovation Solution
A building management system that performs sensor time correction by using an energy manager to cross-correlate time measurements from multiple sensors, identifying a predicted time for object traversal based on distances and average velocity, and determining sensor time errors to synchronize all sensors on a common time base.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If motion sensors use on-board clocks for timing, then the system can operate independently at each sensor, but the timing data becomes misaligned and imprecise across sensors
Solution Approach 1:
The patent merges the timing operations of multiple independent sensors by collecting timing data from all sensors and applying a common time correction factor derived from cross-correlation analysis, thereby maintaining sensor independence while achieving synchronized timing precision across the network
Solution Approach 2:
The system uses feedback by analyzing the collected timing data from multiple sensors, identifying time offsets through cross-correlation, and applying corrections back to the timing data to achieve precise synchronization without requiring hardware modifications to individual sensors
2Measurement precision
If existing systems use broadcast messages or external tools to set sensor time, then time synchronization is attempted, but additional components and complexity are added to the lighting system
Solution Approach 1:
The system performs self-service by using the existing sensor network and timing data to automatically identify time offsets through cross-correlation analysis and apply corrections, eliminating the need for external synchronization tools or additional hardware components
Solution Approach 2:
The timing data collected for occupancy detection serves a dual purpose: it simultaneously provides the basis for identifying time offsets and applying synchronization corrections, making the existing timing infrastructure multi-functional and eliminating the need for separate synchronization mechanisms
3Loss of information
If the central server stores received time and sensor time, then time tracking is attempted, but errors in transmit timing still exist and precision is insufficient
Solution Approach 1:
The patent replaces the mechanical approach of simply storing timestamp values with a signal processing approach using cross-correlation analysis of the actual timing data waveforms, which automatically identifies and corrects timing offsets including those introduced by transmit timing errors
Data Source
AI summary
A building management system and method for sensor time correction is described. The system comprises multiple sensors and an energy manager communicating with the sensors. The sensors, distributed within a particular area, provide multiple time measurements in response to detecting an object traversing among the sensors in which the time measurements are associated with unsynchronized time. The energy manager identifies a predicted time for traversing among the sensors based on one or more distances between pairs of sensors and an average velocity of the object to traverse among the sensors. The energy manager determines a sensor time error for each sensor by cross-correlating the time measurements with the predicted time.