Compensating Element for Thermal Expansion in Piezo Sensor
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Mechanical preload in piezo-driven vibrating limit switches decreases at high temperatures due to differential thermal expansion between ceramic piezoelectric elements and metallic housing components, leading to sensor failure.
Innovation Solution
Incorporation of a compensating element with a higher temperature expansion coefficient than the housing materials to maintain the mechanical preload by adjusting the pressure on the converter unit, ensuring it remains above a predefinable limit value despite temperature-induced changes in housing element distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ceramic piezoelectric elements are used in the transducer unit, then the sensor can generate reliable switching signals at normal temperatures, but at elevated temperatures the metallic housing expands more than the ceramic elements causing the mechanical preload to decrease and sensor failure
Solution Approach 1:
The patent applies the thermal expansion principle by introducing a compensating element made of material with a coefficient of thermal expansion matched to the ceramic piezoelectric elements. This compensating element expands at the same rate as the ceramic elements when temperature increases, maintaining the mechanical preload on the transducer unit despite the differential expansion between ceramic and metallic housing components. The compensating element is positioned in the clamping structure between the housing elements and the transducer unit, allowing it to compensate for thermal effects and prevent sensor failure at elevated temperatures.
2Strength
If the housing and mounting elements are made of metallic materials, then the structural strength and rigidity are sufficient, but these materials expand more than ceramic piezoelectric elements at high temperatures leading to loss of mechanical preload
Solution Approach 1:
The patent uses the compensating element as an intermediary component between the metallic housing structure and the ceramic piezoelectric transducer unit. This compensating element acts as a mediator that absorbs the differential thermal expansion between the metallic housing (which expands more) and the ceramic elements (which expand less). By positioning the compensating element in the clamping path, it transfers the appropriate mechanical preload to the transducer unit while compensating for the thermal expansion mismatch, thereby maintaining reliable operation across a wide temperature range.
3Temperature
If the distance between housing elements serving as clamping elements increases due to thermal expansion, then the housing can accommodate temperature changes, but the mechanical preload on the transducer unit decreases below the required limit
Solution Approach 1:
The patent applies parameter changes by selecting a compensating element with specific material properties (coefficient of thermal expansion) and dimensional parameters (length, cross-section) that are optimized to compensate for the thermal expansion of the housing. By carefully choosing these parameters, the compensating element maintains a substantially constant distance between the clamping surfaces on the transducer unit despite the overall thermal expansion of the housing. This ensures that the mechanical preload force remains within the required limits across the operating temperature range.
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 solution effectively maintains the mechanical preload across a wide temperature range, preventing sensor failure and ensuring reliable operation even at elevated temperatures.
Implementation Method 1
the coefficient of thermal expansion of the compensating element and/or the height of the compensating element along the imaginary axis are selected such that a temperature-related expansion of the compensating element along the imaginary axis during a temperature-related expansion of a housing element to be compensated
Implementation Method 2
at least one transducer unit which excites the mechanically vibrating unit to mechanical vibrations
Implementation Method 3
at least one mechanically vibrating unit, and at least one transducer unit which excites the mechanically vibrating unit to mechanical vibrations and which receives mechanical vibrations from the mechanically vibrating unit
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to a device for determining and/or monitoring a process variable, comprising a housing (2), a unit (1) that can mechanically oscillate, and a converter unit (4), which is arranged and clamped between two housing elements (12, 3, 10) used for clamping such that a pressure that can be predetermined acts upon the converter unit (4) along an imaginary axis. According to the invention, a compensating element (15) is provided, the temperature expansion coefficient and/or height of which is selected such that a temperature-related expansion of the compensating element (15) during a temperature-related expansion of a housing element (8) to be compensated for results in the pressure acting upon the converter unit (4) being greater than or equal a pre-tensioning threshold value that can be predetermined.