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36 a p p e N D I x C accuracy A commercially available handheld thermal camera, the FLIR T300, was used in this study. The specifications for the camera can be found at http://support.flir.com/DsDownload/ Assets/45305-0201_en_41.pdf. According to FLIR, the accu- racy of the temperature readings is ±3.6°F or ±2% of the reading. Images from this system do not indicate depths of defects. However, the images can indicate possible tile debonding, delaminations up to 1 in. deep with a minimum surface area of 1 sq ft, and voids up to 3 in. deep with a minimum surface area of 1 sq ft, based on specimen testing. Such defects can be pinpointed within 1 foot of their actual location. Appendix L provides additional information on the FLIR T300 camera system used in this study, as well as selected images. precision According to FLIR, the precision of the T300 system is less than 0.09°F (0.05°C). The areas of possible defects can be pinpointed within 1 foot of the actual defects as long as the thermal contrast of the area of interest has not changed and the system is properly calibrated. Calibration procedures Each thermal camera manufacturer publishes its own cali- bration procedures (if needed). The user cannot make this calibration; the camera has to be sent to the manufacturer or authorized reseller for calibration. testing procedures The camera operator needs to ensure that the equipment is properly focused before beginning the data collection pro- cess. No other special testing procedures are needed. The researchers used the following process when testing in tunnels: 1. Turn on the camera. 2. Aim the camera at a tunnel lining. Observe the tempera- ture of the lining in the center of the display. 3. Manually set the temperature range to a range of around 5°F (e.g., 60°F to 65°F if the tunnel lining temperature at the center is 62°F). 4. Adjust the range so that a color spectrum appears on the camera display. 5. Aim the camera down the tunnel. With the laser pointer (mounted on the camera), point out areas to personnel where the temperature appears to be higher or lower than usualâaccording to the camera display. 6. Have the personnel inspect the area and determine if the area warrants further investigation by hammer tapping or visual observations of distress or moisture. Mark the area if further investigation is needed. Cost The FLIR T300 handheld thermal camera costs approxi- mately $9,000. Limitations The equipment is not accurate at temperatures below -4°F (-20°C) or above 248°F (120°C). (This is inferred from the FLIR A325 vehicle-mounted thermal camera default calibra- tion.) The normal operating temperature is between 5°F (-15°C) and 122°F (50°C). Data Management Thermal cameras contain data collection and management software. The images are stored on a secure digital (SD) card with the image number and date. The SD card can be removed so the images can be transferred to a computer. Handheld Thermal Camera Testing Criteria
37 Data analysis and Interpretation Thermal camera manufacturers provide data analysis and interpretation software with which the images can be further refined and inspected. For example, FLIR provides free software for data analysis and interpretation of images taken with its equipment. This software is described and can be downloaded at http://www.flir.com/cs/emea/en/ view/?id=42406.
