Abstract
New low-cost measuring devices require that the box housing and electronics have the cost aligned with the sensing system. Nowadays, metallic clips and/or glue are commonly used to fix the electronics to the box, thus providing the same motion of the structure to the sensing element. However, these systems may undergo daily or seasonal thermal cycles, and the combined effect of thermal and mechanical stress can determine significant uncertainties in the measurand evaluation. To study these effects, we prepared some parallel plates capacitors by using glue as a dielectric material. We used different types of fixing and sample assembly to separate the effects of glue softening on the capacitor active area and plates distance. Therefore, we assessed the sample modification by measuring the capacitance variation during controlled temperature cycles. We explored possible non-linear behaviour of the capacitance vs. temperature, and possible effects of thermal cycles on the glue geometry. Further work is still needed to properly assess the nature of this phenomenon and to study the effect of mechanical stress on the sample’s capacitance.
Highlights
Attention about Structural Health Monitoring (SHM) systems, to monitor any possible infrastructure damage, is growing a lot these days [1]: the same attention is not being gained by metrology issues, dealing with the quality of measurements and their reliability
Metallic clips and/or glue are commonly used to fix the electronics to the box, providing the same motion of the structure to the sensing element
We explored possible non-linear behaviour of the capacitance vs. temperature, and possible effects of thermal cycles on the glue geometry
Summary
Attention about Structural Health Monitoring (SHM) systems, to monitor any possible infrastructure damage, is growing a lot these days [1]: the same attention is not being gained by metrology issues, dealing with the quality of measurements and their reliability. There is a chain between the structure surface and the sensing element with many interfaces, influencing the metrological performances of the whole system The presence of these interfaces can generate significant consequences on the measurements, especially when MEMS clinometers and accelerometers are taken into consideration. Being the sensor glued to the enclosing box, when temperature changes (e.g., due to usual environmental thermal shifts), the glue can change its behaviour and geometrical layout Regarding the latter aspect, this implies that a significant systematic error can affect the readout e.g., by introducing a temperature dependant offset, while this effect must be avoided at best to preserve the quality of the measurement. This is accomplished by capacitive measurements on tailored set-ups, as outlined below
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