湖北理工学院 毕业设计(论文)外文文献翻译

外文文献原稿和译文

Multiple single-chip microcomputer approach to

fire detection and monitoring system

A.J. AI-Khalili, MSc, PhD D. AI-Khalili, MSc, PhD M.S. Khassem, MSc

Indexing term : Hazards, Design, Plant condition monitoring

Abstract: A complete system for fire detection and alarm monitoring has been proposed for complex plants. The system uses multiple single chip architecture attached to a party line. The control algorithm is based on a two-level hierarchy of decision making, thus the complexity is distributed. A complete circuit diagram is given for the local and the central station with requirements for the software structure. The design is kept in general form such that it can be adapted to a multitude of plant configurations. It is particularly shown how new developments in technology, especially CMOS single chip devices, are incorporated in the system design to reduce the complexity of the overall hardware, e.g. by decomposing the system such that lower levels of hierarchy are able to have some autonomy in decision making, and thus a more complex decision is solved in a simple distributed method.

1 Introduction

Regulatory requirements for most high risk plants and buildings mandate the installation of fire detection and warning systems for all sensitive areas of the plant or the building. Most fire codes state the requirement for monitoring and control

湖北理工学院 毕业设计(论文)外文文献翻译

specifically related to a type of a plant or building such as chemical plants, petroleum, nuclear plants, residential high-rises etc. A general conclusion of these codes can be specified as the following requirements :

(a) The source of all detector signals should be exactly identifiable by the central station

(b) An extra path of communication between the central station and all local controllers

(c) Direct means of control of alarm and central equipment by the central station (d) Means of communication between the central station and the fire department (e) Availability of emergency power supply. The codes usually also specify the types and frequency of tests for all equipment.

A fire detection and alarm system is a combination of devices designed to signal an alarm in case of a fire. The system may also accomplish fan control, fire door hold or release, elevator recall, emergency lighting control and other emergency functions. These additional functions supplement the basic system which consists of detection and alarm devices and central control unit.

Technology has an influence on system architecture. When technology changes, the architecture has to be revised to take advantage of these changes. In recent years, VLSI technology has been advancing at an exponential rate. First NMOS and, in the last year or two, CMOS chips have been produced with the same packing density with more gates per chip yet at a lower power consumption than NMOS. Surely this change in technology must affect our design of hardware at both the chip and the system level. At the chip level, single chips are now being produced which are equivalent to board levels of only the previous year or two. These chips have microprocessor, memory in RAM and ROM, IO Ports both serial and parallel, A/D timer, flags and other functions on chip. At the system level, the new chips make new architectures possible. The objective of this paper is to show how technology can influence system architecture in the field of fire control. The new high density single chip microcontrollers are incorporated in the design of a large scale system and yet we obtain a smaller system with a better performance. In terms of fire detection and

湖北理工学院 毕业设计(论文)外文文献翻译

alarm monitoring, this is reflected directly in the local station hardware, because of their remoteness and power supply requirements. A complete local station can be designed around a single CMOS chip with power consumption of a few m W depending on system operation. This approach reduces the cost and complexity of design, implementation and maintenance and provides easily expandable and portable design. This implementation was not possible with old technology. Most of fire detection/monitoring systems available are tailored towards a specific application and lack the use of recent advances in CMOS VLSI technology. In this study, we develop a fire detection/monitoring system which is general in concept, readily implementable in a multitude of applications for early detection of a fire before it becomes critical, for equipment and evacuation of personnel. Here, we propose a central control and distributed control/detection/monitoring with adequate communication, where use is made of single-chip microcontrollers in the local stations, thus improving controllability and observability of the monitoring process.

2 Detection and alarm devices

A basic fire detection system consists of two parts, detection and annunciation. An automatic detection device, such as a heat, smoke or flame detector, ultraviolet or infrared detectors or flame flicker, is based on detecting

the byproduct of a combustion. Smoke detectors, of both ionization and optical types, are the most commonly used

detector devices. When a typical detector of this type enters the alarm state its current consumption increases

from the pA to the mA range (say, from a mere 15pA in the dormant mode to 60 mA) in the active mode. Inmany detectors the detector output voltage is well defined under various operating conditions, such as those

given in Table 1. The more sensitive the detector, the more susceptible it is to false alarms. In order to control the

detector precisely, either of the following methods is used: a coincidence technique

湖北理工学院 毕业设计(论文)外文文献翻译

can be built into the detector, or a filtering technique such that a logic circuit becomes active only if x alarms are detected within a time period T. The detection technique depends greatly on the location and plant being protected; smoke detectors are used for sleeping areas, infrared or ultraviolet radiation are used when flammable liquids are being handled, heat detectors are used for fire suppression or extinguishing systems. In general, life and property protection have different approaches.

Alarm devices, apart from the usual audible or visible alarms, may incorporate solid state sound reproduction and emergency voice communication or printers that record time, date, location and other information required by the standard code of practice for fire protection for complex plants. Heaviside [4] has an excellent

review of all types of detectors and extinguisher systems.

2.1 Control philosophy and division of labour

Our control philosophy is implemented hierarchically. Three levels of system hierarchy are implemented, with two levels of decision making. There is no communication between equipment on the same level. Interaction between levels occurs by upwards transfer of information regarding the status of the subsystems and downwards transfer of commands. This is shown in Fig. 1 where at level 1 is the central station microcomputer and is the ultimate decision maker (when not in manual mode). At level 2 are the local controllers, which reside in the local stations. At level 3 are the actual detectors and actuators. A manual mode of operation is provided at all levels.

Information regarding the status of all detectors is transmitted on a per area basis to the local controllers. Their information is condensed and transmitted upward to the central microcomputer. Transfer of status is always unidirectional and upwards. Transfer of commands is always unidirectional and downwards, with expansion at the local control level. This approach preserves the strict rules of the hierarchy for exact monitoring detection and alarm systems associated with high risk plants.