On structured fault tree construction by modularizing control loops

The objectives of this article are: (1) to develop the fault trees for cont rol loops in a way that they all appear in a proper form and as modules in the fault tree for the whole system; and also (2) to modularize each contro l loop in a system properly to establish its unit model. These two methods are essentially equivalent. Either of them can be applied to facilitate con structing fault trees for the whole system. To accomplish such equivalent o r parallel objectives, we will first take the feedback and feedforward cont rol loops in the heat exchanger system as examples and then: (1) construct the fault trees of deviations in controlled variable for the two control lo ops in the way that all of their nonbasic terminal events should be deviati ons in variables on those streams that connect to the loop from their outsi de in the system; and (2) establish the unit model for each of such two loo ps. One of the purposes of (2), which will not be addressed here, is to reg ard each control loop as a dummy unit and hence reduce the system to facili tate system input and fault tree construction eventually for complete autom ation purpose. (C) 2000 Elsevier Science Ltd. All rights reserved.