**3. Decision-level fusion for bearing fault diagnosis**

In above section, we have proposed a simple, fast and good performance fault diagnosis approach. This approach is based on single sensor source and using individual classifier. It can obtain high accuracy on the multiple fault types recognition problems under the same fault degree. But when under multiple fault degrees, it declines in performance. To deal with this problem, this section will introduce a new method based on decision-level fusion for bearing fault diagnosis. The new fusion method includes four stages. These four stages are vibration signal acquisition and decomposition, fractal feature parameter extraction, single data source fault diagnosis and decision-level fusion for fault diagnosis. The first three stages are the same with the method described in the above section. So, we only state the last step in this section.
