**2.2. Online measurements**

An online measurement system was designed to measure slab broadening at the exit of the caster.(FU JianXun et al. 2011(b)) The system comprises an optical lens, a digital camera, a data cable (IEEE 1394), and a computer. The system is controlled using the computer. The digital camera is used to take infrared images of the hot slab. Data is read from the camera at a preset frequency.

**Figure 1.** Online width measurement system for hot slabs.( FU JianXun et al. 2011(b))

Then, the graphics module creates images of the hot slab according to color aberration, and saves the images as files. The accuracy of the online system is 1 mm. A photograph of the system is shown in Figure 1.
