Optimal Structure of Sensor Systems with Two Failure Modes

An optimal sensor structure is developed for a sensor system which consists of several channels. Each channel monitors a particular plant state, e.g., temperature or pressure. When some states become abnormal, an event occurs. The channels which monitor these abnormal states then initiate appropriate safety systems. Sensors are either good, or failed-dangerous, or failed-safe. More than one sensor is available for each channel. The problem is to obtain the optimal s-coherent sensor structures for the channels. A theorem is proven and a nonlinear integer programming (NLIP) problem is derived to minimize s-expected total damage. The NLIP problem can be solved by the extended Lawler & Bell algorithm. For a 1-channel sensor system, the optimal structure can be obtained analytically by a simple formula.