Inductive Proximity Switch Circuit for Low-Current A/D Sampling
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Solution Overview
Problem
Existing non-contact inductive proximity switches face challenges in reducing power requirements while maintaining analog-to-digital conversion for environmental parameter processing, particularly due to high current demands during analog-to-digital conversion, which exceed the recommended leakage and minimum load currents.
Innovation Solution
Implementing an A/D converter that operates only at certain time intervals, powered by a storage capacitor connected to a microcontroller, and charging during periods of sufficient current availability, such as during comparator threshold exceedance or in phases of low power demand, allowing for power-saving modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog-to-digital conversion is performed continuously to maintain accurate temperature compensation, then measurement precision is improved, but current consumption increases beyond recommended limits
Solution Approach 1:
The A/D converter is operated periodically at specific time intervals rather than continuously. The microcontroller triggers the A/D converter to perform analog-to-digital conversion only during designated measurement phases, reducing overall current consumption while maintaining adequate temperature compensation through periodic measurements
Solution Approach 2:
The system performs temperature measurements and A/D conversions in advance during periods when current consumption is acceptable, storing the converted values in memory for later use in compensation calculations, thereby avoiding the need for continuous high-current operation
2Measurement precision
If A/D converter is operated at full capacity to ensure accurate environmental parameter processing, then measurement precision is improved, but the leakage current and minimum load current exceed 500μA
Solution Approach 1:
The A/D converter is activated periodically rather than continuously, with measurement cycles synchronized to periods when the proximity switch is not in active switching mode. This periodic operation reduces the average leakage current below the 500μA threshold while still providing sufficient measurement data for accurate environmental parameter processing
Solution Approach 2:
The system dynamically adjusts the operation of the A/D converter based on the operational state of the proximity switch. During active switching periods, the A/D converter is disabled to minimize leakage current; during idle or measurement periods, it is activated to perform conversions when current draw is acceptable
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 significantly reduces the overall current requirement, enabling the proximity switch to maintain accurate temperature compensation without exceeding recommended current limits, thus optimizing power usage and extending operational stability under varying conditions.
Implementation Method 1
the A/D converter is supplied from a storage capacitor which, via a resistor, is connected to a pin of a microcontroller
Implementation Method 2
Inductive proximity switches have at least one sensor coil and can be operated both with current pulses and with continuous, mostly sinusoidal alternating current. The change in the inductance and/or the impedance of a coil
Data Source
Figure 1
AI summary
The invention relates to an inductive proximity switch having at least one sensor coil (1) for producing an alternating magnetic field for detecting an electrically conductive target in a monitoring zone, said proximity switch having an oscillator circuit (2) for feeding the sensor coil (1), an evaluating circuit (3) connected to the sensor coil (1) for producing a binary switching signal, and a microcontroller (4) connected to the evaluating circuit (3), wherein the switching signal is influenced by a correction value, characterized in that a storage capacitor (5) that feeds the microcontroller (4) is connected to a connection of the evaluating circuit (3) by means of a resistor (6) and is charged by the evaluating circuit (3) only intermittently.