Capacitive Probe Layered Structure for Turbomachine Gap Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive probes used in turbomachines face challenges with temperature-related stress cracks due to differing thermal expansion coefficients of materials like ceramic and metal, limiting their service life and measurement accuracy at high temperatures.
Innovation Solution
A probe design featuring a layered structure with cohesive connections between metal, metal alloys, and electrically conductive ceramics, allowing unhindered thermal expansion and avoiding stress cracks, combined with a shielding sleeve to maintain high mechanical stability and measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a triaxial structure with ceramic and metal materials is used, then measurement capability is achieved, but stress cracks occur due to different thermal expansion coefficients at high temperatures
Solution Approach 1:
The probe structure is divided into separate coaxial layers with insulator elements positioned between conductive elements. This segmentation allows each material layer to expand independently according to its own thermal expansion coefficient, preventing stress cracks while maintaining the functional triaxial structure for capacitance measurement.
Solution Approach 2:
Electrically non-conductive insulator elements are introduced as intermediary components between the electrically conductive measuring elements and shield elements. These insulator elements act as buffers that accommodate differential thermal expansion between metal and ceramic materials, preventing direct stress transmission that would cause cracks.
2Strength
If all elements are made of ceramic materials with similar thermal expansion coefficients, then stress cracks are avoided, but material choice is limited and manufacturing becomes complex and expensive
Solution Approach 1:
The patent changes the material parameter approach from requiring uniform thermal expansion coefficients to allowing different coefficients by introducing insulator elements. This enables the use of conventional materials like metals and ceramics with standard properties, simplifying manufacturing while avoiding stress cracks through the insulator buffer layers.
3Measurement precision
If metal or metal alloys are used for the measuring element, then measurement accuracy is improved, but thermal expansion differences with ceramic materials cause stress cracks
Solution Approach 1:
The probe employs a composite structure with alternating layers of electrically conductive materials (metal or metal alloys for measuring elements) and electrically non-conductive materials (insulator elements). This composite arrangement allows metal measuring elements to provide high measurement accuracy while the insulator layers prevent thermal stress cracks by accommodating expansion differences.
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 probe achieves long service life and high measurement accuracy by allowing free thermal expansion of materials and shielding against interference, preventing stress cracks and ensuring reliable operation in high-temperature environments.
Implementation Method 1
capacitive sensor device... for capacitively measuring the distance from a stationary or passing object
Implementation Method 2
temperature expansion of the individual elements is possible almost unhindered... different coefficients of thermal expansion
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to a probe for a capacitive sensor device with an outer sleeve (12) and at least one probe head (14) arranged within the outer sleeve (12), said probe head comprising a measuring element (46) with at least one measuring and front face (16), the measuring element (46) being made of a metal, a metal alloy or an electrically conductive ceramic or being coated at least at the measuring and front face (16) with a metal, a metal alloy or an electrically conductive ceramic, a first electrically non-conductive isolator element (18) and a first partial element (22) of a first shield (20), wherein the first partial element (22) is made of a metal, a metal alloy or an electrically conductive ceramic. According to the invention, the measuring and front face (16), the first isolator element (18) and the first partial element (22) of the first shield (20) are adhesively connected to one another and configured as a multilayer, the first isolator element (18) being disposed between the measuring element (46) with its measuring and front face (16) and the first partial element (22). The invention also relates to a gap-measuring system for determining a rotor gap between a rotor comprising rotor blades and a rotor housing, which surrounds at least sections of the rotor or rotor blades, of a turbomachine using the probe (10) according to the invention.