1 ENCAPSULATION AND UNCERTAINTIES OF STRAIN-GAUGE SENSORS FOR STRESS-MONITORING OF CONSTRUCTIONS

Strain gauges are an important tool in measuring techniques applied to determine loads and detect dam-ages. Due to their high signal-resolving power, they are also suitable for stress analysis in building con-structions. Without specific encapsulation, they are, however, suitable only for short-term measurements. Therefore, a completely new encapsulation type was developed at PTB. The strain gauges were placed in a sensor housing which protects the sensitive technology- similar to common force transducers- and is fitted into a small measurement borehole of the structure. These applied investigations were part of the work of a collaborative research center of the German Research Foundation. Based on these investigations, the measurement uncertainty of the sensor will be analyzed and the final design for commercial production and calibration of this new sensor type presented. An additional impor-tant result of this research project was the development of a new type of plastic encapsulation for the strain gauges inside that sensor. The encapsulation was tested in thermostatic hot water baths, in climatic chambers similar to those of DIN IEC 68 2-30 and in outdoor tests