Capacitive Occupancy Detector Heating Circuit Diagnostic
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Solution Overview
Problem
Capacitive occupancy or proximity detection systems that use a heating element as an antenna electrode face challenges due to the need for expensive inductors with high AC impedance, which are cumbersome and costly, and require monitoring for safety-relevant system integrity to prevent false readings.
Innovation Solution
A capacitive occupancy or proximity detector is designed with a heating circuit, impedance measurement circuit, and diagnostic circuit that includes a heating current sensor, current supply device, and current limiting ground path to diagnose the heating circuit's integrity while it is on or off, using a diagnostic current to determine if a short circuit or circuit interruption has occurred, and measuring resistance to assess the heating circuit's condition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a heating element is used as an antenna electrode in a capacitive occupancy detector, then the system can be simplified and cost reduced, but the heating circuit requires expensive inductors with high AC impedance to isolate heating current from the sensing circuit
Solution Approach 1:
The patent introduces a diagnostic circuit as an intermediary component that measures the actual impedance of the heating element and compares it against expected values. This mediator allows the system to verify proper isolation of the heating circuit without requiring expensive high-AC-impedance inductors, thereby reducing component costs while maintaining system functionality.
Solution Approach 2:
The patent replaces the traditional approach of using passive high-impedance inductors for isolation with an active diagnostic measurement system. Instead of relying on the physical properties of expensive inductors to provide isolation, the system uses electronic measurement and comparison to verify circuit integrity, substituting a costly passive component with a more economical active diagnostic approach.
2Device complexity
If a heating element is used as an antenna electrode, then component count is reduced, but system integrity monitoring becomes critical to prevent false readings
Solution Approach 1:
The patent implements a feedback mechanism where the diagnostic circuit continuously monitors the impedance of the heating element and compares it against predetermined reference values. This feedback loop provides real-time verification of heating circuit integrity, alerting the system to any deviations that could cause false occupancy readings, thereby maintaining high reliability despite the dual-use configuration.
Solution Approach 2:
The patent performs preliminary diagnostic measurements of the heating element's impedance before the occupancy detection function is activated. By checking the heating circuit's integrity in advance and comparing measured values against expected ranges, the system ensures that the heating element is properly isolated and functioning correctly before relying on it for capacitive sensing, preventing false readings from occurring.
3Ease of manufacture
If the heating circuit and sensing circuit share the same heating element, then manufacturing cost decreases, but the risk of false occupancy detection increases without proper diagnostic monitoring
Solution Approach 1:
The diagnostic circuit serves as an intermediary verification layer that measures the actual electrical characteristics of the heating element and compares them against expected values for proper isolation. This mediator ensures that the dual-use heating element maintains the correct electrical separation between heating and sensing functions, preventing false occupancy detection while allowing the cost-effective shared component design.
Solution Approach 2:
The patent replaces expensive high-AC-impedance inductors with a diagnostic measurement system that electronically verifies circuit isolation. By using active measurement and comparison instead of passive high-cost components, the system achieves the same reliability goal at lower manufacturing cost, maintaining occupancy detection accuracy while reducing overall system cost.
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
This configuration allows for reliable diagnosis of the heating circuit, preventing false readings and ensuring the system's integrity, thereby enhancing the accuracy and safety of capacitive detection without the need for expensive inductors.
Implementation Method 1
A capacitive occupancy or proximity detector comprises a heating element (12) connected between a first and a second node (14, 16), which are provided for connecting the heating circuit to a heating current source (18)
Implementation Method 2
A capacitive sensor generally comprises at least one antenna electrode, to which is applied an oscillating electric signal and which thereupon emits an electric field into a region of space proximate to the antenna electrode
Implementation Method 3
The object to be sensed modifies the capacitance between the transmit electrode and ground
Implementation Method 4
The relationship of voltage to current yields the complex impedance of the one or more antenna electrodes
Data Source
AI summary
A capacitive occupancy or proximity detector (10) comprises a heating circuit, an impedance measurement circuit (34, 36, 40) and a diagnostic circuit. The heating circuit includes a heating element (12). The impedance measurement circuit is connected to the heating element so as to measure impedance between the heating element and a node at ground potential. The diagnostic circuit is configured for measuring electrical resistance across the heating circuit and includes a heating current sensor (42), configured for sensing a heating current across the heating circuit, a current supply device (48) for driving a diagnostic current across the heating circuit and a current limiting ground path (50), configured for draining the diagnostic current and for blocking the heating current.