Rail Vehicle Speed Measurement Using XOR Logic
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Solution Overview
Problem
Existing methods for determining the speed of rail-bound vehicles are limited by the need for detection devices to be mounted at a minimum distance of 2000 mm to ensure accuracy, which can lead to inefficiencies and increased assembly work, and struggle with pulse length variations and overlapping pulses.
Innovation Solution
Generating an XOR signal by linking detection pulses and determining the time difference between their centers using an XOR gate, allowing for accurate speed measurement even with close device placement and overlapping pulses, utilizing a binary counter device to calculate the duration of the XOR signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If detection devices are mounted at a minimum distance of 2000 mm to ensure measurement accuracy, then speed measurement accuracy is improved, but assembly work and device complexity increase
Solution Approach 1:
The patent changes the evaluation parameter from measuring the time difference between rising edges of detection pulses to measuring the duration of the XOR signal. This parameter transformation allows accurate speed measurement even when detection devices are mounted at smaller distances, as the XOR signal duration automatically accounts for pulse width variations and overlapping pulses, eliminating the need for 2000 mm minimum spacing
Solution Approach 2:
The XOR gate acts as an intermediary element that processes the two detection pulses from closely-spaced detection devices. By generating an XOR signal whose duration represents the time difference between pulse centers, the intermediary handles the complexity of pulse width variations and overlapping, allowing simple duration measurement instead of complex rising edge alignment
2Ease of manufacture
If detection devices are placed close to one another to reduce assembly work, then ease of manufacture is improved, but pulse overlapping occurs reducing measurement reliability
Solution Approach 1:
The patent converts the harmful effect of overlapping pulses into a beneficial feature. Instead of avoiding overlap by spacing devices 2000 mm apart, the invention embraces close placement and uses the XOR operation to extract meaningful information from overlapping pulses. The XOR signal duration correctly represents the time difference between pulse centers even when pulses overlap, transforming the reliability problem into a robust solution
Solution Approach 2:
Instead of trying to prevent pulse overlapping by increasing distance, the patent inverts the approach by using logical XOR operation that naturally handles overlapping conditions. The XOR truth table (output is true when inputs differ) automatically produces a signal whose duration equals the time difference between pulse centers, regardless of whether pulses overlap or not
3Device complexity
If the time difference is determined by measuring distance between rising flanks of detection pulses, then the method is simple, but measurement precision decreases when pulses have different lengths
Solution Approach 1:
The patent transforms the measurement parameter from rising edge time difference to XOR signal duration. This parameter change inherently accounts for pulse width variations because the XOR operation's output duration is mathematically equal to the absolute difference between the centers of the two input pulses, regardless of their individual widths. This eliminates the precision loss that occurs when pulses have different lengths
Data Source
AI summary
A method for determining the speed of a rail-bound vehicle, includes the following method steps: detection of a reference element, wherein the first detection device generates a first detection signal when the reference element passes the first detection device; detection of the reference element, wherein the second detection device generates a second detection signal when the reference element passes the second detection device; conversion of the detection signals into digital detection pulses; determining the time difference between the two detection pulses; wherein an XOR signal is generated in an XOR gate by linking the first and the second detection pulse using an XOR logic; and the duration of the XOR signal is determined; and wherein the time difference between the two detection pulses is determined by halving the duration of the XOR signal. The speed can be measured with higher accuracy when using an existing infrastructure without additional assembly work.