Bridge Displacement Measurement Using Geophone Analog Compensation
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Solution Overview
Problem
Current methods for measuring bridge span displacement, such as high-power lasers and radar interferometers, are expensive and complex, while indirect measurements using accelerometers and geophones suffer from significant errors due to axis positioning errors and require costly digital filters for compensation.
Innovation Solution
A measuring system comprising a geophone with a resonance frequency greater than the bridge's oscillation frequency range, coupled with an analogue compensation device and integrator, provides a stable and cost-effective indirect measurement of bridge span displacement by compensating frequency response within the bridge's resonance band using analogue filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high power laser is used for direct measurement, then measurement precision is improved, but device cost and energy consumption increase significantly
Solution Approach 1:
The patent replaces complex optical measurement systems (laser, radar interferometer) with a simple geophone-based mechanical vibration sensing system. The geophone converts bridge span vibrations into electrical signals that can be processed to obtain displacement information, eliminating the need for expensive and complex optical equipment while maintaining measurement capability.
Solution Approach 2:
The patent changes the measurement approach from direct displacement measurement using high-precision optical instruments to indirect measurement through vibration frequency analysis. By measuring the natural frequency of the bridge span and comparing it before and after loading, displacement can be calculated using the relationship between frequency, stiffness, and mass, thereby avoiding the need for complex direct measurement systems.
2Device complexity
If accelerometric sensors with MEMs technology are used for indirect measurement, then device cost is reduced, but measurement precision deteriorates due to error propagation from axis positioning errors
Solution Approach 1:
The patent replaces accelerometric sensors with geophones, which are velocity sensors with a different frequency response characteristic. The geophone's natural high-pass filter characteristic is compensated through analog circuitry, providing accurate displacement measurement without the positioning sensitivity issues that plague accelerometers.
Solution Approach 2:
The patent introduces an analog compensation circuit as an intermediary between the geophone and the measurement system. This circuit compensates for the geophone's frequency response characteristics, particularly the attenuation at low frequencies and the resonance peak, thereby enabling accurate displacement measurement across the relevant frequency range without requiring expensive digital filtering.
3Measurement precision
If geophones with digital filters are used for indirect measurement, then measurement precision is improved, but device cost increases
Solution Approach 1:
The patent replaces expensive digital filtering systems with a simple analog compensation circuit. The analog circuit uses passive components (resistors, capacitors) to compensate for the geophone's frequency response, providing cost-effective frequency correction without requiring complex digital signal processing hardware or software.
Solution Approach 2:
The patent extracts only the essential frequency compensation function from complex digital filtering systems and implements it through a dedicated analog compensation circuit. This extraction approach provides the necessary frequency response correction while eliminating the cost and complexity of full digital filtering systems.
4Ease of operation
If geophones are used for indirect measurement, then ease of operation is improved, but measurement precision deteriorates due to frequency response limitations below 4 Hz
Solution Approach 1:
The patent introduces an analog compensation circuit as an intermediary that corrects the geophone's frequency response characteristics. The circuit compensates for the natural high-pass filter behavior and resonance peak, extending the accurate measurement range down to very low frequencies (0.1 Hz and below) where bridge spans typically operate.
Solution Approach 2:
The patent changes the effective frequency response of the geophone system through analog compensation. By adjusting the compensation circuit parameters (resistor and capacitor values), the system can be tuned to flatten the frequency response across the relevant measurement range, enabling accurate low-frequency displacement measurement while maintaining the geophone's operational simplicity.
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
The system enables accurate, inexpensive, and simple indirect measurement of bridge span displacement by minimizing errors and eliminating the need for expensive digital filters, allowing for easy repositioning of the geophone for different measurements.
Implementation Method 1
The geophone 11 is able to detect the oscillations of the bridge to which it is applied and generates an electrical signal whose magnitude is proportional to the speed at which the bridge and therefore the geophone 11 are displaced by oscillating
Data Source
AI summary
A measuring system for measuring the displacement of at least one point of a bridge, wherein the bridge has a resonance frequency included in the frequency band [fl, fh] where fl<fh, the measuring system including: a geophone adapted to be applied in the at least one point of the bridge, the geophone having a resonance frequency fr greater than fh and a frequency response for f<fh substantially equal to that of a double shunt; an analogue compensation device connected in series to the geophone and having a frequency response equal to that of a double integrator in the frequency band [fl, fh]; an analogue integrator device connected in series to the analogue compensation device; and an analogue/digital converter device connected in series to the analogue integrator device, the analogue/digital converter device being adapted to convert the output signal from the analogue integrator device into a digital signal.