Heating Wire Circuit Switching for Capacitive Sensing Accuracy
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Solution Overview
Problem
Existing electric heating systems in vehicles face issues with parasitic capacitances from field effect transistors causing interference in capacitive detection, and high thermal stress leading to heating wire failure and sensitivity fluctuations.
Innovation Solution
A circuit structure using MOS-FETs for efficient heating and capacitive measurement, with alternating modes and controlled switching to minimize parasitic capacitances and thermal stress, incorporating a detecting circuit for capacitive measurement and a testing phase to ensure reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If field effect transistors are used to separate heating wire from heating potentials during measuring mode, then capacitive detection interference is reduced, but parasitic capacitances from the transistors cause measurement disturbances
Solution Approach 1:
The patent extracts the heating wire from the heating potential connections during measuring mode by opening switching elements, separating the capacitive sensing function from the heating function. This extraction eliminates the primary source of parasitic capacitance interference while maintaining the ability to perform accurate capacitive detection.
Solution Approach 2:
The patent introduces a capacitor connected in parallel with the heating wire as an intermediary element to compensate for parasitic capacitances. This additional capacitor acts as a mediator that counterbalances the harmful parasitic capacitances from switching elements, thereby improving measurement accuracy.
2Measurement precision
If additional impedances such as diodes are used to support insulating effect during measuring mode, then capacitive detection interference is reduced, but ohmic losses affect heating current efficiency
Solution Approach 1:
The patent employs periodic switching of the heating wire between heating mode and measuring mode. During measuring mode, switching elements are opened to eliminate parasitic capacitance interference. During heating mode, the same switching elements are closed to provide low-impedance current paths, avoiding continuous energy losses from protective impedances.
Solution Approach 2:
The patent changes the electrical state parameters of switching elements dynamically - transitioning from conducting state during heating mode to non-conducting state during measuring mode. This parameter change allows the system to optimize for either heating efficiency or measurement accuracy at different times, avoiding continuous energy losses.
3Adaptability or versatility
If heating wire is used for both heating mode and capacitive measuring mode alternately, then component versatility is improved, but thermal stress causes heating wire failure and sensitivity fluctuations
Solution Approach 1:
The patent implements periodic alternation between heating mode and measuring mode, allowing the heating wire to rest from thermal stress during measuring intervals. This periodic interruption of heating cycles reduces cumulative thermal stress and prevents overheating, thereby improving reliability while maintaining versatility.
Solution Approach 2:
The patent provides beforehand cushioning by introducing compensation capacitors that counteract the effects of thermal stress and aging on the heating wire. These capacitors compensate for sensitivity fluctuations caused by thermal expansion and material degradation, maintaining reliable operation over extended periods.
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
Ensures reliable capacitive detection by minimizing interference and thermal stress, maintaining efficient heating power, and allowing for calibration and integrity testing of the heating wire.
Implementation Method 1
the heating wire, which is a resistance wire, for example, such as a nickel-chrome wire, is flooded with an electric heating current supplied by two poles at two different heating potentials, wherein a heating voltage drops on the heating wire
Implementation Method 2
use the heating wire, during a non-heating phase, as an electrode for a capacitive approach detection in the so-called measuring mode
Data Source
AI summary
The present disclosure relates to a circuit and a method for carrying out an alternating heating and capacitive measuring mode by a common heating wire, including carrying out a heating mode, wherein, due to a switching by a control circuit, first switching elements and second switching elements are connected in series to the heating wire, and the heating wire is connected, to one of two heating potentials; triggering a switchover from the heating mode into a measuring mode by the control circuit; carrying out the measuring mode, in which the measuring capacitance of the heating wire relative to a reference potential is determined by a detecting circuit by applying to the heating wire an alternating voltage; carrying out a testing phase by a test circuit that is switched by the control circuit that a test impedance is connected to the measuring capacitance.