Experimental Investigation of the Performance of the SOFO Measurement System

The SOFO system is a fiber optic measurement system based on low coherence interferometry. It was introduced by SMARTEC and is widely used for structural health monitoring. To date more than 3500 sensors have been installed in various types of buildings, ranging from power plants to highway bridges. Initially, the SOFO system was developed for long-term monitoring within a wide temperature range. Thus issues like temperature insensitivity and long-term stability are of great importance. We show that for most applications the temperature dependence of the reading unit can be neglected. However, for high precision measurements the temperature of the reading unit should be measured and a correction function should be applied. If a linear correction function is used a precision of 2µm can be achieved within a temperature range of -10°C to 40°C. Further, it is demonstrated that the accuracy of the reading unit is stable for at least 1½ years.