Safe Digital Input Circuit for Cross-Circuit Interference Isolation
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Solution Overview
Problem
Existing safety technologies, such as 3-wire and 4-wire schemes, fail to accurately detect cross-circuits between inputs in safety-critical systems, particularly in environments where connecting cables are protected, leading to potential undetected interference voltages that can compromise system safety.
Innovation Solution
A safe digital input circuit with diodes in the signal lines between the clock generator output and clock outputs, preventing feedback effects of interference voltages and allowing granular resolution of affected lines, while using a microcontroller for fast evaluation and error messaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 3-wire scheme is used with protected connecting cables, then device complexity is reduced, but measurement precision deteriorates because cross-circuits cannot be detected
Solution Approach 1:
The patent segments the clock signal path by introducing separate clock lines (S1, S2) for each input channel, with individual diodes (D1, D2) protecting each segment. This segmentation allows independent detection of interference voltages on each line while maintaining overall system simplicity.
Solution Approach 2:
The diodes D1 and D2 act as intermediary protective elements between the clock generator output and the respective clock lines. These intermediaries prevent feedback effects from interference voltages while allowing the clock signal to pass through, enabling detection without adding complex protection infrastructure.
2Reliability
If diodes are added to prevent feedback effects, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent changes the electrical parameters of the clock signal path by introducing diodes with specific forward voltage characteristics. This parameter change enables the system to distinguish between valid clock signals and interference voltages, improving reliability through electrical parameter differentiation rather than complex logic.
Solution Approach 2:
The diodes introduce asymmetric behavior to the otherwise symmetric dual-clock-line system. The diodes conduct in one direction only, creating asymmetric protection that prevents feedback effects from interference voltages while allowing legitimate clock signals to pass, thereby improving reliability with minimal additional components.
3Measurement precision
If separate clock lines are used for each input, then measurement precision is improved for detecting interference voltages, but device complexity increases
Solution Approach 1:
The clock signal path is segmented into separate lines (S1, S2) for each input channel, with individual diode protection (D1, D2) on each segment. This segmentation enables precise localization of interference voltages to specific lines while maintaining a relatively simple overall configuration that leverages the existing dual-clock-line architecture.
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
Enables precise detection and isolation of interference voltages at individual inputs, ensuring rapid system response and protection against excessive interference, thereby enhancing safety in safety-critical applications.
Implementation Method 1
a first diode is interposed in the first signal line between the clock generator output and the first clock output and a second diode is interposed in the second signal line between the clock generator output and the second clock output, so that a feedback effect on the respective other signal line (S1, S2) caused by an interference voltage (60, 61) is prevented
Data Source
AI summary
A safe digital input circuit with a first input and a second input for reading in a sensor signal with a clock generator to generate a clock signal is shown. The safe digital input circuit includes a first clock output and a second clock output for connecting sensors to safely shut down a plant. A first and a second signal line are connected to a clock generator output of the clock generator to forward the clock signal to the first and second clock output.