Dynamic Pulse Width Adjustment for PLC Output Switch Circuit Diagnosis
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Solution Overview
Problem
Existing abnormality diagnosis methods for output switch circuits, particularly in PLCs used in factory automation, face challenges in diagnosing devices always in the ON state due to the lack of an OFF command instance, leading to potential erroneous detection during dark tests caused by variations and temperature fluctuations in semiconductor components.
Innovation Solution
A dark test method that gradually increases the diagnosis pulse width until a response pulse is detected, allowing for the smallest possible pulse width to be used, automatically adjusting for variations and temperature fluctuations, and diagnosing the output switch circuit as abnormal when the pulse width exceeds a specified limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed diagnosis pulse width is used in dark test, then the test can be performed, but erroneous detection occurs due to variations and temperature fluctuations in semiconductor components
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed diagnosis pulse width to a dynamically adjustable pulse width that adapts to actual circuit characteristics. The system performs preliminary measurements to determine the actual ON/OFF timing of the output switch circuit and adjusts the diagnosis pulse width accordingly, allowing the test to accommodate variations in semiconductor components and temperature fluctuations while maintaining diagnosis accuracy.
Solution Approach 2:
The patent implements parameter changes by modifying the diagnosis pulse width based on measured characteristics of the output switch circuit. The system measures the actual response time of the circuit and adjusts the pulse width parameter to match the actual behavior, thereby compensating for component variations and environmental conditions without requiring manual parameter modifications.
2Reliability
If manual parameter modification is required for component replacements, then diagnosis accuracy can be maintained, but device complexity and maintenance burden increase
Solution Approach 1:
The patent applies self-service by enabling the system to automatically adjust the diagnosis pulse width without requiring manual intervention. The output diagnosis unit performs preliminary measurements, determines the actual characteristics of the output switch circuit, and autonomously sets the appropriate pulse width parameter, eliminating the need for manual parameter modification when components are replaced.
Solution Approach 2:
The patent implements feedback by using the measured response characteristics of the output switch circuit to automatically adjust the diagnosis pulse width. The system measures the actual ON/OFF timing, uses this feedback information to calculate the appropriate pulse width, and applies the adjusted parameter in subsequent tests, creating a closed-loop system that maintains accuracy without manual intervention.
3Measurement precision
If a longer diagnosis pulse width is used to ensure detection, then response pulse can be detected, but the pulse width cannot be minimized and may cause unnecessary delays
Solution Approach 1:
The patent applies dynamics by determining the minimum necessary pulse width through preliminary measurements rather than using a fixed conservative value. By measuring the actual response time of the output switch circuit, the system sets the pulse width to the smallest value that ensures reliable detection, thereby reducing unnecessary time delays while maintaining detection accuracy.
Data Source
AI summary
A dark test method for diagnosing presence or absence of an abnormality in an output switch circuit configured to output a voltage signal for switching ON and OFF an output device includes performing a test process including: outputting, to the output switch circuit a switch signal having an OFF pulse form with a diagnosis pulse width; and determining whether or not a response pulse having an OFF pulse form can be detected from an output detection signal obtained by digitally converting the voltage signal output from the output switch circuit. The test process is repeated while gradually increasing the diagnosis pulse width until the response pulse can be detected. It is determined that the output switch circuit is abnormal when the diagnosis pulse width reaches or exceeds a specified upper limit value.