Capacitive Sensor Electrode Pulse Timing for Low-Emission Evaluation
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Solution Overview
Problem
High-frequency cyclic charging of capacitive sensor electrodes in capacitive proximity switches leads to unwanted electromagnetic alternating fields, violating regulatory restrictions on electromagnetic emissions.
Innovation Solution
The method involves varying the charging pulse durations during the evaluation process, allowing for a flexible design and operation of capacitive sensor electrodes by changing the duration of coupling and decoupling cycles, which reduces frequency-dependent radiation peaks and broadens the signal spectrum, thereby minimizing electromagnetic emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-frequency cyclic charging is used to ensure reliable capacitance evaluation in sufficient time, then evaluation speed is improved, but electromagnetic radiation increases violating regulatory restrictions
Solution Approach 1:
The patent applies dynamics by making the charging frequency variable rather than fixed. The control unit dynamically adjusts the charging frequency between a first frequency and a second frequency during the evaluation process. This dynamic frequency variation prevents the sensor electrode from consistently operating at frequencies that generate harmful electromagnetic radiation, while still maintaining sufficiently high evaluation speeds through periodic high-frequency charging cycles.
Solution Approach 2:
The patent implements periodic action by alternating between different charging frequencies in a structured manner. The control unit switches between the first charging frequency and the second charging frequency during the evaluation process. This periodic frequency modulation ensures that electromagnetic radiation is limited by reducing time spent at high frequencies, while still achieving reliable capacitance evaluation through periodic high-frequency measurement cycles.
2Device complexity
If fixed charging frequency is used to simplify control, then device complexity is reduced, but electromagnetic radiation peaks increase at specific frequencies
Solution Approach 1:
The patent applies dynamics by implementing variable frequency control through a control unit that can switch between at least two different charging frequencies. This dynamic frequency adjustment prevents the system from being locked into a single frequency that might coincide with resonant frequencies of the sensor electrode or surrounding structures, thereby avoiding concentrated electromagnetic radiation peaks while maintaining manageable control complexity through predefined frequency switching logic.
3Loss of time
If high charging frequency is used to reduce measurement time, then evaluation speed is improved, but the sensor electrode acts as an antenna emitting electromagnetic radiation
Solution Approach 1:
The patent implements periodic action by using periodic frequency modulation to alternate between high and low charging frequencies during the evaluation process. This allows the system to achieve reliable capacitance measurement through periodic high-frequency cycles while limiting overall electromagnetic emission by spending significant time at lower frequencies. The periodic switching pattern ensures that measurement accuracy is maintained while reducing total exposure to harmful electromagnetic radiation.
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 approach allows for reliable capacitance evaluation at higher frequencies while adhering to regulatory limits, enhancing flexibility in sensor design and operation, and increasing evaluation speed.
Implementation Method 1
The sensor electrode forms a capacitance with a reference electrode
Implementation Method 2
the electrostatic properties of the entire system change
Implementation Method 3
the sensor electrode is coupled to a charging circuit during a coupling time period tK. During the coupling of the sensor electrode to the charging circuit, the sensor electrode is partially or fully charged with electrical charge
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3a~3b
AI summary
The invention relates to a method for evaluating the capacitance value of a capacitive sensor electrode. The method comprises an evaluation process with the following steps: - performing a charging process of the sensor electrode, - evaluating a parameter that depends on the capacitance value of the sensor electrode. A first charging pulse duration tL,1, which consists of a first coupling duration tK,1 and a first decoupling duration tE,1 with tL,1 = tK,1 + tE,1, of a first coupling and decoupling cycle, and a second charging pulse duration tL,2, which consists of a second coupling duration tK,2 and a second decoupling duration tE,2 with tL,2 = tK,2 + tE,2, of a second coupling and decoupling cycle immediately following the first coupling and decoupling cycle, differ from each other by a first pulse duration deviation ΔtL,1.