Industrial systems serve us in all areas of life. Faults may result in economic loss and wasting energy. Detecting the onset of faults, and determining their location are important engineering tasks. An important class of fault detection and diagnosis methods utilizes the mathematical model of the monitored system. But, the parameters required for mathematical modeling is limited or unavailable for the most real industrial engineering applications. Observer-Based Fault Detection (FD) is one of the main approaches to fault detection and identification. Meanwhile, the traditional observer gain calculation required system model parameters. So, this paper presents the design of a novel observer for FD purposes using the Input-Output measurements of the system with unknown parameters. And, this proposed observer design considers observer gain tuning, regardless of the mathematical representation of the plant. This the new feature that distinction our observer will facilitate the implementation of FD systems for many unknown parameters industrial systems. The effectiveness of the proposed observer is verified by experimental application to BLDC motor and compared with classical Luenberger observer. The experimental and comparisons results are proofed feasible and effective of the proposed observer for FD purposes.