The satellite recharges its batteries using solar energy. As the it orbits the Earth, its position relative to the Sun changes, taking its power-supply subsystem through four distinct stages: battery charging, solstice, eclipse, and battery reconditioning. Using qualitative modelling, we constructed a simulation with which the behaviour of the power supply in each stage could be predicted. By provoking simulated faults in the components, we used the simulation to generate examples of how each fault would affect the supply's behaviour. From these examples, the ILP program Golem induced a set of rules for diagnosing power supply failures. In generating the examples, faults were provoked in all possible components, thus guaranteeing that the rules are complete and correct for all single faults.
Because the power-supply's behaviour changes with time, the formalism used to describe the examples must be able to express a fault's dependence on time. We have developed such a formalism, which is based on temporal logic and which is suitable for ILP learning.
The arrows indicate the flow of supply. The qualitative model of this system consists of about 40 components and 29 sensors [Pearce D.A.(1988)].
An important feature of this system is that the diagnosis of some faults is not possible with simple classification rules. These faults usually require the history of related components. For example, a simple check of power from the battery is not sufficient to determine if it is faulty. We need to know the history of other components in the circuit before this can be decided. Although many different faults can be simulated, the concern here is with battery faults. The information used is as follows:
fault(32)states that there was a fault at time instance 32.
The sensors in the power subsystem are as follows:
tm040_switch : system switch status indicator. tm018_switch : system switch status indicator. tm031_switch : system switch status indicator. m038_switch : system switch status indicator. tm022_switch : system switch status indicator. tm043_switch : system switch status indicator. tm013_switch : system switch status indicator. tm042_switch : system switch status indicator. tm007_switch : system switch status indicator. tm222_charging : battery charging status indicator. tm071_asr_or_switch_20: system switch status indicator. tm070_supply_3c : power supply from solar. tm058_asr_or_switch_10: system switch status indicator. tm057_supply_2c : power supply from solar. tm257_battery_voltage : system battery status indicator. tm017_switch : system switch status indicator. tm009_switch : system switch status indicator. tm220_supply_1c : power supply from solar. tm055_supply_1b : power supply from solar. tm054_supply_1a : power supply from solar. tm029_ovt_disabled : battery over-temperature blocking signal. tm021_eoc_disabled : battery end-of-charging indicator. tm004_eoc_signaled : battery end-of-charging blocking signal. tm002_battov_temp : battery over-temperature sensor. tm039_eod_disabled : battery end-of-discharging blocking signal. tm015_eod_signaled : battery end-of-discharging indicator. tm011_eod_override : battery end-of-discharging overwriting signal. tm001_eod_relay : battery end-of-discharging relay switch. tm211_bus_voltage : system power bus status.
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