Push-Pull Proximity Switch Evaluation for Wire Break Detection
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Solution Overview
Problem
Existing proximity switches with PNP or NPN outputs face limitations in mechanical design due to the inability to distinguish between a normal switching state and a wire break fault, necessitating complex mechanical configurations to ensure at least one switch is always damped, increasing costs and design constraints.
Innovation Solution
Employing a proximity switch with a push-pull output and an evaluation unit that includes an electrical circuit and evaluation logic to detect fault conditions, particularly wire breaks, by ensuring at least one output is always active, allowing differentiation between undamped states and wire breaks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a proximity switch with PNP or NPN output is used, then the switching function is achieved, but wire break faults cannot be distinguished from normal switching states
Solution Approach 1:
The output stage is segmented into two independent push-pull outputs (first output and second output) that can be independently controlled. This segmentation allows the system to provide distinct signal states for different conditions (damped vs. undamped) and enables fault detection by monitoring both outputs simultaneously, resolving the inability to distinguish wire breaks from normal states.
Solution Approach 2:
An intermediary evaluation unit is introduced between the proximity switch and the control system. This evaluation unit includes an electrical circuit with two output paths and evaluation logic that monitors the signals from both outputs. The intermediary detects wire break faults by identifying when neither output provides a valid signal, thereby distinguishing faults from normal switching states without modifying the fundamental proximity sensing mechanism.
2Reliability
If two proximity switches are used to detect wire break faults, then reliability is improved, but mechanical design complexity and costs increase
Solution Approach 1:
The functionality of two separate proximity switches is merged into a single proximity switch with a push-pull output stage that has two outputs. The electrical circuit combines the sensing element with dual output drivers, allowing one physical device to perform the work of two switches while providing both damped/undamped detection and wire break detection capabilities through signal processing in the evaluation unit.
Solution Approach 2:
The proximity switch with push-pull output is designed with multi-functionality: it can detect the damped/undamped states for speed monitoring and simultaneously detect wire break faults through the same output stage. The evaluation unit processes both functions using the two outputs, eliminating the need for separate switches dedicated to fault detection and reducing mechanical design complexity.
3Reliability
If at least one proximity switch must be damped at all times, then wire break detection is possible, but mechanical design freedom is restricted
Solution Approach 1:
The evaluation unit implements feedback monitoring of both push-pull outputs to detect wire break faults. By continuously evaluating the signal states from both outputs and providing feedback about the system's health status, the system can detect faults without imposing constraints on the mechanical design. The feedback mechanism allows the use of symmetric, cost-effective mechanical components while maintaining fault detection capability.
Data Source
Figure 1
AI summary
The invention provides an evaluation unit (100) for evaluating an output signal of a push-pull output of a proximity switch (400), comprising: - an electrical circuit (200) with at least one input (430) and a first and second output (531, 532; 541, 542), wherein the input (430) is connectable to the push-pull output of the proximity switch (400), and wherein the electrical circuit (200) is configured to output a signal at the first output (531, 532) when the input (430) is switched to a positive potential, and to output a signal at the second output (541, 542) when the input (430) is switched to ground, and - at least one evaluation logic (310, 320) connected to the first and second output of the electrical circuit, which is configured to detect an error condition. Furthermore, the invention provides for a system with a proximity switch and such an evaluation unit.