Inductive Proximity Sensor LC Circuit Metal Housing
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Solution Overview
Problem
Existing inductive proximity sensors face limitations in providing accurate and reliable results, especially when used in fully metal housings or under conditions of mechanical stress and aggressive environments, due to the influence of metal components on oscillator quality and frequency, and errors in detection caused by transitional signal states.
Innovation Solution
The inductive proximity sensor employs an LC circuit switched between two states, allowing the coil to freely oscillate, with voltage signal amplitude measured at a predefined point after switching, and the results calculated in relation to reference measurements to determine object distance and material nature, using a capacitor as the supplying means and a switching mechanism driven by a periodical pulse signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an oscillator of high quality is used to provide a sensor launching with a relatively low threshold, then detection sensitivity is improved, but the sensor cannot be used with detectors in fully metal housings as the quality of the oscillator would strongly decrease
Solution Approach 1:
The patent applies periodic action by using a capacitor to repeatedly charge and discharge the coil in periodic cycles, creating periodic current pulses through the coil without requiring a high-quality oscillator. This periodic excitation method generates the necessary magnetic fields for detection while being insensitive to metal housing interference, thus resolving the contradiction between detection sensitivity and compatibility with metal housings
Solution Approach 2:
The patent extracts the oscillator from the system entirely, replacing it with a simple capacitor-based periodic charging mechanism. By removing the oscillator component that is sensitive to metal housing interference, the sensor can be used with fully metal housings while still achieving the necessary detection performance through the periodic current pulses generated by capacitor discharge
2Measurement precision
If a coil is directly supplied with periodical transmitting current pluses and voltage induced is integrated over a relatively short time window, then a smoothened useful signal is obtained, but evaluation during transitional state results in errors in detection and sensing
Solution Approach 1:
The patent applies preliminary action by allowing the coil current to decay completely before evaluating the signal. The evaluation is performed after a predetermined time period following the current pulse, ensuring that all transient effects have disappeared. This timing strategy eliminates detection errors caused by transitional states while maintaining signal quality through proper signal integration
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 enables accurate and reliable detection of metallic objects, including ferromagnetic and non-ferromagnetic materials, with improved stability and reduced errors, even in metal housings, by ensuring consistent oscillation and exponential amplitude decay measurement.
Implementation Method 1
an inductive coil defining a front working plane of the sensor and associated with a covering plate or a plane part of a housing... means for supplying the coil or inductance repeatedly with current... said induced voltages being influenced by the presence of objects or bodies within a given detection area
Implementation Method 2
the measuring circuit comprised of an oscillator working at resonance conditions oscillates at its maximum amplitude... said coil or inductance being part of a LC circuit... the LC circuit is repeatedly switched between two states... the LC circuit being allowed to freely oscillate while in said second state
Implementation Method 3
When a metallic object approaches the active part of the switch, it generates losses by Foucault currents induced in said object and thus a decrease of the amplitude of the resonance
Data Source
AI summary
An inductive proximity sensor includes a coil or inductance arranged in the vicinity of an active surface or end of the sensor, a current source repeatedly supplying the inductance, and a signals processor for signals corresponding to the voltages induced in the coil when fed. The induced voltages are influenced by the presence of objects within a given detection area, depending on their distance and on their constituting material. The coil or inductance is part of a parallel LC circuit. The current source is the capacitor of the LC circuit. A voltage signal amplitude measurement is performed after each switch from charge to discharge state. The result is computed using reference measurements to calculate a distance, a nature of the constituting material, and/or mass indicative value of the objects.