Current DAC Fault Detection in Sensor Control Circuits
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Solution Overview
Problem
Existing sensor systems with current DA converters cannot detect failures in switching elements, leading to abnormal control current outputs due to on-failure or off-failure of these elements, as the control current instruction values are not accurately measured.
Innovation Solution
A method is introduced that generates an inspection current instruction value sequence to detect failures in the current DA converter, where inspection current values are sequentially inputted and detected to identify bit failures by comparing actual output currents with predicted values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the control current instruction value is used as the magnitude of the control current without measuring the actual current, then the device complexity is reduced and ease of operation is improved, but the reliability deteriorates due to undetected switching element failures
Solution Approach 1:
The patent applies preliminary action by performing failure detection before the system operates in normal mode. An inspection current instruction value sequence is generated and input to the current DAC during an inspection period, enabling the system to detect switching element failures before they affect normal control current output. This preliminary inspection resolves the contradiction by adding a detection mechanism that doesn't interfere with the simplicity of normal operation.
Solution Approach 2:
The patent introduces an intermediary inspection current instruction value sequence that mediates between the simple digital control approach and the need for reliability verification. This intermediary signal allows the control unit to indirectly verify the health of switching elements by comparing expected inspection current values with actual measured values, without requiring continuous complex monitoring during normal operation.
2Measurement precision
If switching elements are added to the current DAC output stage to increase precision, then the measurement precision is improved, but the device complexity increases due to more switching elements that can fail
Solution Approach 1:
The patent applies feedback by measuring the actual inspection current output from the current DAC and comparing it with the expected inspection current values. This feedback mechanism enables detection of deviations caused by switching element failures, allowing the system to maintain measurement precision awareness without adding complex continuous monitoring circuitry. The feedback is activated only during inspection periods, balancing precision requirements with device complexity.
3Reliability
If the inspection current instruction value sequence is input to detect failures, then the reliability is improved through failure detection, but the productivity decreases due to inspection time requirements
Solution Approach 1:
The patent implements periodic action by performing failure detection at specific inspection periods rather than continuously. The control unit alternates between inputting normal control current instruction values during operation and inspection current instruction value sequences during inspection periods. This periodic inspection approach maintains reliability through regular failure detection while minimizing impact on productivity by limiting inspection to discrete time intervals.
Data Source
AI summary
A sensor system (1, 1S) including a current DA converter (42) outputting a control current (Ip) of a sensor element (3S), a control unit (4C) generating a control current instruction value (Ipcmd) corresponding to magnitude of the control current and inputting this instruction value to the current DAC, an instruction value sequence generating unit (47) generating, instead of the control current instruction value, an inspection instruction value sequence (RChcmd) in which predetermined inspection current instruction values (Chcmd) inputted to the current DAC are arranged in order and by which failure of the current DAC can be detected, an inspection current detection unit (71) detecting an inspection current value (Ichv) of an inspection current (Ich) outputted from the current DAC, and a failure detection unit (8) detecting failure of the current DAC from an inspection current value sequence (RIchv) in which the inspection current values are arranged in order of detection.