1 research outputs found
Qualitative modelling and simulation of physical systems for a diagnostic purpose
This is a Milton Keynes De Montfort University thesisThe goal of a fault-diagnosis system is to obtain an accurate diagnosis at a low cost. In order to
reach this goal, many techniques have been used, e.g. qualitative methods and multiple-models.
This research investigates a novel strategy for improving the balance accuracy versus cost of
consistency-based fault-diagnosis systems.
This new strategy is organised around the notion of entities. These are physical entities. such as
water pressure or temperature. The functioning of a physical system can involve numerous entities.
Because these entities influence each other's behaviour, multiple-fault situations can occur, where
several entities are affected by a fault. These situations are called complex multiple-fault situations.
The existing fault-diagnosis systems do not perform satisfactorily on complex multiple-fault
situations. This is because the set of entities they investigate is fixed from the start of the diagnostic
process. As a consequence, depending on the entities included in this set, existing systems either
perform an inaccurate diagnosis, or reach an accurate diagnosis at an unnecessarily high cost. This
thesis presents a fault-diagnosis strategy called MVDS (standing for Multiple Variable Diagnosis
Strategy) designed specifically for performing the efficient diagnosis of complex multiple-fault
situations. The underlying principle of MVDS is that it is not possible to know from the start of the
diagnostic process which entities are affected. Thus, a diagnostic process with MVDS is
undertaken with the investigation of an initial set of entities, and this set of investigated entities is
continuously updated along the process, as intermediate results are obtained.
In order to illustrate clearly the functioning of MVDS, a fault-scenario using a small example from
the air-conditioning domain is diagnosed and the process studied. The investigation of the
performance of MVDS on more complex physical systems is undertaken on a larger case-study
using a hot-water and heating system. In MVDS, it is possible to disable the adaptability of the set
of investigated entities, so that it can be run with a fixed set. By doing so, the performance of the
strategy in MVDS can be compared to the performance of traditional approaches which use a fixed
set of investigated entities.
The study-case shows that MVDS reaches more accurate results than traditional approaches, and
that this accuracy is obtained at a low cost, since unnecessary measurements of entities are avoided.
Furthermore, the strategy produces a complete trace of the process that is close to common-sense
reasoning. It is also a co-operative strategy where the operator can intervene.
Summary of the main research contributions:
- The issue of diagnosing complex multiple-fault situations is specifically addressed for the first
time. The problem caused by this diagnosis task is defined, and a strategy is constructed in order to
diagnose efficiently the complex multiple-fault situations. The strategy is implemented in MVDS
and tested on an example and a case-study.
- Risk characteristics have been described. They allow to evaluate how prone to complex muItiple-fault
situations is a physical system.
- Hot-water and heating systems are offered as a new domain of research for consistency-based
fault-diagnosis systems.
- The inclusion of co-operation into the fault-diagnosis process is a novel approach. Its potential
advantages have been identified