Open Load Diagnosis Using In-Band Voltage Transients
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Solution Overview
Problem
Existing methods for open load diagnosis in signal line systems are inadequate for real-time detection within digital systems, particularly in motor vehicle and industrial applications where reliable detection of external load conditions is crucial for functional safety.
Innovation Solution
A device and method for open load diagnosis that applies a first stable voltage and a second different voltage to a signal line within specific voltage limits, performs a time constant-dependent measurement, and compares the results to determine the resistance of the load, allowing for real-time signaling of open load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a voltage is applied to the signal line for open load diagnosis, then the load resistance can be measured, but the signal line may leave the logic voltage band causing incorrect logic states
Solution Approach 1:
The patent applies a voltage that changes over time rather than a static voltage level. The voltage starts at a first level within the logic band, transitions to a second level also within the logic band, and returns to the first level. This time-varying parameter approach enables RC time constant measurement while maintaining logic state validity throughout the measurement process.
Solution Approach 2:
The diagnosis method uses a periodic voltage application cycle: apply voltage to reach a second level, hold for measurement, then return to the first level. This periodic action allows repeated measurements without permanent disruption to the signal line's logic state, enabling continuous monitoring while preserving system reliability.
2Reliability
If the signal line voltage is changed for measurement, then load conditions can be detected, but real-time operation of the signal line is disrupted
Solution Approach 1:
The patent performs the voltage application and measurement during designated diagnosis intervals before normal signal transmission resumes. The controller is configured to apply the diagnostic voltage only during specific time windows when no critical data transmission is occurring, thereby preparing the measurement condition in advance without disrupting ongoing operations.
Solution Approach 2:
The system dynamically switches between diagnosis mode and normal operation mode. The controller monitors timing signals and dynamically applies the diagnostic voltage only during appropriate intervals, allowing the signal line to alternate between being used for data transmission and being used for load diagnosis, thus maintaining both detection capability and operational continuity.
3Measurement precision
If a voltage outside the logic band is applied for measurement, then accurate resistance measurement is achieved, but the signal line logic state becomes invalid
Solution Approach 1:
Instead of applying a single high-voltage pulse outside the logic band, the patent uses a controlled voltage transition within the logic band. The voltage changes from a first level to a second level (both within the logic band) and back, creating a measurable transient response that provides sufficient information for resistance calculation without exceeding voltage limits that would invalidate the logic state.
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 reliable and real-time open load diagnosis in digital systems, ensuring functional safety in motor vehicle and industrial applications by accurately determining load conditions without disrupting the signal line's logic state.
Implementation Method 1
to perform a time constant dependent measurement so as to determine a value of a parameter which is or depends on resistance of a load between the signal line and a reference line
Data Source
AI summary
A device for open load diagnosis of a signal line in a digital system in which a logic state is represented by a band of voltages lying between first and second voltage limits is described. The device is configured to cause the signal line to reach a first, stable voltage lying in the band, to apply a second, different voltage to the signal line lying in the band and without leaving the band, to perform a time constant dependent measurement so as to determine a value of a parameter which is or depends on resistance of a load between the signal line and a reference line, to compare the value of the parameter with a reference value of the parameter and, in dependence on comparison, to signal the result.