Opposing-Sensor THz Measurement for Pipe Wall Thickness
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Solution Overview
Problem
Existing THz measurement methods for pipes face challenges such as deviations in pipe shape causing unanalyzable back reflections, strong absorption of THz radiation leading to unreliable signal evaluation, and the need for precise knowledge of the material's refractive index, which varies with temperature and batch, making accurate wall thickness measurement difficult.
Innovation Solution
A THz measuring method and device using a sensor arrangement with two opposing sensors that perform measurements from two opposite positions, allowing for calibration without requiring knowledge of the material's refractive index by determining the idle time and distance, and calculating wall thicknesses based on time-of-flight measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a one-sided measurement method is used with radially arranged sensors, then the device complexity is reduced, but measurement reliability deteriorates due to unanalyzable back reflections from pipe shape deviations and strong absorption of THz radiation
Solution Approach 1:
The measurement system is segmented into multiple independent measurement paths with sensors arranged at different positions (e.g., 0°, 90°, 180°, 270°) around the pipe. Each sensor independently measures wall thickness at its specific location, allowing the system to handle shape deviations and absorption issues at individual positions while maintaining overall measurement reliability.
Solution Approach 2:
The measurement approach transitions from a single radial measurement point to multiple angular positions around the pipe circumference. This dimensional expansion from one-point to multi-point measurement enables the system to capture variations in pipe shape and material properties, resolving the reliability issue caused by localized shape deviations and absorption.
2Measurement precision
If the refractive index is determined for each material batch and temperature condition, then measurement precision is improved, but the loss of time increases due to required calibration measurements
Solution Approach 1:
The system performs preliminary calibration measurements to determine the relationship between transit time ratios and refractive index before actual production measurements. This preliminary characterization allows the system to store pre-determined calibration data, eliminating the need for time-consuming recalibration for each material batch or temperature change while maintaining measurement precision.
Solution Approach 2:
The system uses feedback from measured transit times to automatically determine the refractive index based on pre-established calibration relationships. By continuously monitoring transit time ratios and comparing them against stored calibration data, the system adaptively determines material properties without requiring manual recalibration, thus reducing time loss while maintaining precision.
3Ease of operation
If THz radiation is used for measuring pipe wall thickness, then non-contact measurement is achieved, but the absorption of THz radiation by the material causes signal loss and unreliable evaluation
Solution Approach 1:
The measurement system segments the THz signal analysis into multiple components: direct transmission signal, back-reflection signal from the inner wall, and signals from the outer wall. By analyzing the ratio and time-of-flight of these segmented signal components, the system compensates for absorption losses and maintains reliable evaluation even with strong material absorption.
Solution Approach 2:
The system uses the air gap or fluid medium inside the pipe as an intermediary reference medium. By comparing the transit time of THz radiation through the pipe wall material versus through the intermediary medium, the system can determine wall thickness while compensating for absorption effects, maintaining both non-contact operation and signal reliability.
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 measurement of pipe wall thickness and diameter without needing to know the refractive index, allowing for continuous monitoring of material quality and composition, even with varying temperatures and material batches, and providing additional information on material behavior.
Implementation Method 1
The THz radiation is partially reflected at interfaces between materials with different refractive indices, particularly at the outer and inner surfaces of a pipe profile
Implementation Method 2
allowing the time of flight of the THz measurement signal to be determined
Data Source
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AI summary
The invention relates to a THz measurement method for surveying a measurement object (6), for example a pipe made of plastic or rubber, comprising - a calibration step of measuring an unbroken time of flight of at least one THz emission beam through an empty run length between a first measurement position (MP1) and a second measurement position (MP2) of a measurement area (4) without the measurement object (6) and ascertaining the empty run length (sO), - positioning a measurement object (6) in the measurement area (4) between measurement positions (MP1, MP2), - performing a first THz measurement from the first measurement position (MP1) with a THz emission beam (20-1) along a first optical axis (A) while measuring a first external time of flight (tL1) to an outer surface (6a) of the measurement object (6), a first wall time of flight (tR1) through a first wall area of the measurement object (6) and an internal time of flight (tL2, tL2_1) through an interior (6c) of the measurement object, - performing a second THz measurement from the second measurement position (MP1) along a second optical axis (A) while measuring a second external time of flight (tL3) between the second measurement position (MP2) and the outer surface (6a) of the measurement object (6) and a second wall time of flight (tR2) through a second wall area of the measurement object (6) - ascertaining an overall time of flight (tges_R) through the measurement area (4) containing the measurement object, and - ascertaining a first wall thickness (sR1) of the first wall area and a second wall thickness (sR2) of the second wall area from the measured times of flight (St7).