Fault tolerance is achieved through hardware redundancy in repeated hardware elements to provide protection against localised damage in safety-critical systems. Examples of such systems include aircraft, space vehicles, nuclear power plants and plants handling dangerous chemicals. One method in achieving fault detection and fault isolation is through hardware cross monitoring, where the performance of the repeated components is continuously assessed and compared. This technique is simple to apply and is widely used. The drawbacks include the extra hardware cost and the additional space required to accommodate the duplicated equipment. In this chapter, this technique will be presented to calculate the threshold values on a multi-lane actuator in torque and velocity summed architectures. The brushless dc motors in both architectures will be represented by their lumped models. The FDI system (discussed in Chapter 5) will be implemented to monitor the actuator for failures in feedback transducers as well as the currents in each lane.

Chapter Contents:

• 6.1 Peak lane disparities
• 6.2 Scheduled threshold setting, STS - failure transients and aircraft response
• 6.3 Unscheduled threshold setting (UTS) - a simulation graphical Monte Carlo (SGMC) approach

Inspec keywords: electric actuators; redundancy; fault diagnosis; brushless DC motors

Other keywords: torque summed architectures; hardware cross monitoring; multi-lane actuator; FDI system; safety-critical systems; actuator lumped models; localised damage; threshold values; fault tolerance; brushless dc motors; velocity summed architectures; feedback transducers; hardware redundancy

Subjects: Small and special purpose electric machines; Control gear and apparatus; d.c. machines; Electric actuators and final control equipment