Housekeeping Unit

The present Housekeeping Unit (HU) (Figure A.7) was designed in 1990, and is based on a similar, older system that proved reliable for many years. It is based on the 6502 microprocessor and the firmware is written in assembler and stored in EPROM. It also has non-volatile RAM with a real-time clock, a serial interface, A/D converter, a number of digital-I/O interfaces, various sensors and controls. The housekeeping unit is powered by uninterrupted 12 V DC (max 1 A) from the lead-acid battery.

Figure A.7: The ALIS Housekeeping Unit.

The housekeeping unit monitors battery and mains voltages, outdoor- dome- filter- and ambient temperatures, illumination level, fire- and trespass alarm sensors, precipitation (snow/rain) and the proper functioning of the station computer. It controls the power distribution unit, the environment control unit (Section A.2) and the access to the dial-up communication line.

If the station computer ceases to function properly, the housekeeping unit will take actions to bring the station into a safe state and alert the control centre of the situation. By sending commands directly to the housekeeping unit it is then possible to diagnose the situation and restart the station. Due to this solution, almost no trips to the stations have been required for system malfunctions.

The present housekeeping unit has been in use since 1991 and proven very reliable but must unfortunately soon be replaced as many of its components are obsolete. The next generation of housekeeping units will be based on a number of networked micro-controllers, possibly with a GSM telephone as a redundant communication link.