Calibration of Asphalt Strain Transducers by Using Digital Image Correlation

Full-scale pavement testing often utilizes embedded instrumentation to measure the effect of traffic loading. As with any scientific measurement, confidence in the data from these sensors relies on proper calibration and installation. Manufacturers of sensors typically perform calibration tests before shipment, but these tests are not standardized. In addition, some manufacturers provide only one calibration sheet covering a batch of sensors, while others provide calibration results for each sensor. Many transducers are calibrated to produce voltage sensitivity factors; however, not all data acquisition systems accept these as inputs. This was the case at the pavement testing facility of the Minnesota Department of Transportation, where a new data acquisition system required gauge factors. This paper describes the development of a bench calibration testing procedure that uses a digital image correlation system to determine system gauge factors (SGFs) for two types of asphalt strain transducers. The calibration results clearly show that each transducer has a unique SGF that should be used when transforming collected strain data. Although the procedure that was developed produced consistent SGFs between tests, several improvements are recommended. The variations in SGFs found in this study demonstrate the need for fully understanding the calibration of strain transducers and the data acquisition systems to which they are connected.