Capacitive Occupancy Detector Heating Element Integrity Monitoring
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Solution Overview
Problem
Capacitive occupancy or proximity detection systems using a heating element as an antenna electrode face challenges in monitoring the integrity of the heating element, which is crucial for accurate detection, due to the high cost of precision amplifiers required for measuring heating current and resistance.
Innovation Solution
A capacitive loading mode measurement circuit employing a common mode choke as a separator between heating and measurement currents, coupled with a diagnostic circuit that injects a DC current through the heating element and detects voltage variations using a microcontroller, allows for a low-cost seat heater diagnostic system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If precision amplifiers are used to measure heating current and resistance for monitoring heating element integrity, then measurement precision is improved, but device cost increases significantly
Solution Approach 1:
The patent introduces a common mode choke as an intermediary component between the heating element and the measurement circuit. The choke's inductance provides natural impedance that enables measurement of heating element integrity without requiring expensive precision amplifiers. The measurement circuit measures current through the common mode choke, which reflects the heating element's resistance changes, thereby achieving accurate monitoring at low cost.
Solution Approach 2:
The patent replaces the electronic measurement approach (using precision amplifiers and transimpedance amplifiers) with a magnetic field-based approach. The common mode choke utilizes electromagnetic induction to convert changes in heating element resistance into measurable voltage or current signals, substituting complex electronic measurement systems with a simpler electromagnetic sensing mechanism.
2Reliability
If the heating element is continuously monitored during heating cycles, then reliability is improved, but energy consumption increases
Solution Approach 1:
The patent implements periodic monitoring of the heating element by controlling the switching element to cycle between ON and OFF states. During each heating cycle, the monitoring occurs at specific intervals (when the switching element transitions states) rather than continuously. This periodic measurement approach maintains reliability by detecting heating element integrity at critical moments while significantly reducing overall energy consumption compared to continuous monitoring.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables effective monitoring of the heating element's integrity at a lower cost, ensuring accurate capacitive detection without the need for expensive precision amplifiers, and can diagnose the heating circuit both during and outside heating cycles.
Implementation Method 1
a common mode choke having a first and a second winding, said heating element being connectable to said heating current source via said first and second windings of said common mode choke
Implementation Method 2
A capacitive occupancy or proximity detector comprises a heating circuit, an impedance measurement circuit and a diagnostic circuit for checking the integrity of the device
Implementation Method 3
an oscillating voltage signal is applied to a transmit electrode, which builds up an oscillating electric field to ground. The object to be sensed modifies the capacitance between the transmit electrode and ground
Data Source
AI summary
A capacitive occupancy or proximity detector includes a heating circuit, an impedance measurement circuit connected to the heating element, and a diagnostic circuit configured for determining integrity of the heater element. The heating circuit includes a heating element, a heating current source and a common mode choke having a first and a second winding, the heating element being connectable to the heating current source via the first and second windings. The diagnostic circuit includes at least one controllable switching element coupled across the second winding, circuitry for injecting a DC current into a series connection formed by the first winding the heating element and a parallel connection of the second winding and the at least one controllable switching element, and at least one detection circuit for detecting a voltage variation across the second winding.