Field Device Dual-Timer Self-Diagnosis for Process Automation
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Solution Overview
Problem
In process automation, field devices face challenges in preventing unnecessary interventions during temporary errors without losing safety-related information, as existing self-monitoring and diagnostic systems often result in immediate reporting of errors, leading to potential shutdowns and disruptions.
Innovation Solution
The field device employs a diagnostic device with two timers: a first timer for outputting a substitute value when the error expires and a second timer for reporting errors, allowing continued operation if the error is resolved within the first timer's expiry time, with the second timer's shorter expiry time ensuring timely error reporting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If immediate error reporting is implemented, then safety-related information is preserved, but unnecessary interventions and process disruptions occur
Solution Approach 1:
The system dynamically adjusts the error response based on the duration of the fault condition. Two timers are implemented: a first timer (T1) that triggers substitute value output after a first expiry time, and a second timer (T2) that triggers error reporting after a second expiry time. This dynamic timing mechanism allows the system to tolerate temporary errors while maintaining safety monitoring for persistent faults.
Solution Approach 2:
The system prepares substitute values in advance for critical process variables. When a sensor detects a fault, the diagnostic device can immediately output pre-prepared substitute values from memory, avoiding process disruption. This preliminary preparation of backup values enables continuous operation during temporary sensor failures.
2Productivity
If temporary errors are tolerated to maintain process continuity, then productivity is preserved, but safety-related information may be lost
Solution Approach 1:
The system uses two different expiry times to create a dynamic response strategy. The first timer (T1) with longer expiry time allows process continuity by tolerating temporary errors. The second timer (T2) with shorter expiry time ensures safety monitoring by reporting persistent errors. This dynamic dual-timer approach balances productivity and safety requirements.
Solution Approach 2:
The diagnostic device acts as an intermediary between the sensor and the process control system. It monitors sensor functionality, manages substitute value output, and controls error message generation. This intermediary layer filters temporary errors from critical faults, allowing process continuity while maintaining safety monitoring through structured error handling.
3Productivity
If substitute values are output immediately upon error detection, then process continuity is maintained, but measurement accuracy deteriorates
Solution Approach 1:
The system dynamically determines when to output substitute values based on timer expiry. The first timer (T1) controls the duration for which substitute values are output. Only after T1 expires does the system switch to error reporting mode via the second timer (T2). This dynamic switching maintains process continuity during temporary errors while preserving measurement validity by avoiding premature substitute value output.
Solution Approach 2:
The field device performs self-diagnosis and self-correction through automatic substitute value output. When a sensor fault is detected, the diagnostic device automatically activates backup measurement channels or calculates substitute values without external intervention. This self-service capability maintains measurement precision by using alternative valid measurement paths rather than immediate substitute values.
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a field device which outputs a measured value (4) and also has a self-diagnosis function, which, when at least one specified error (F2) is detected, signals said error by means of a first binary status signal (11), marks the output measured value (4) as temporarily invalid by means of a second binary status signal (12), and initiates the output of a substitute value (15) instead of the measured value (4). The substitute value is used to trigger a safety-oriented response. In order to prevent such a serious intervention in the process sequence when temporary errors occur, but without losing safety-relevant information, the field device contains a first timer having a specified first expiration time (FRD) and a second timer having a specified shorter second expiration time (FID). Both timers are started when the error (F2) is detected and are reset at the end of the detected error (F2). The first timer initiates the output of the substitute value (15) when the first expiration time (FRD) expires. The second timer signals the error (F2) by means of the first binary status signal (11) when the second expiration time (FID) expires, wherein the signal can be reset by means of an acknowledgement signal (13) if, at the same time, the output measured value (4) is marked as valid by means of the second binary status signal (12).