Thorn security MR300 User Manual (English)

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DOCUMENT CONTROL NUMBER /

M300 SERIES

01A-02-D4

02 2/97

Registered Ofﬁce: Security House The Summit Hanworth Road Sunbury-on-Thames Middlesex TW16 5DB

EQUIPMENT:

PUBLICATION:

ISSUE No. & DATE:

MR300 OPTICAL SMOKE DETECTOR RANGE

PRODUCT APPLICATION & DESIGN INFORMATION

1. INTRODUCTION

The MR300 range of optical smoke detectors forms part of the

M300 series of plug-in detectors for ceiling mounting. The

range is intended for two-wire operation on the majority of the

control equipment currently manufactured by the company. De-

tectors having different smoke sensitivities are offered as is an

intrinsically-safe type for use in hazardous atmospheres.

2. OPERATING PRINCIPLE

2.1 OPTICAL SYSTEM

Detectors in the MR300 range detect visible particles produced

in ﬁres by using the light scattering properties of the particles.

All detectors in the range use the same optical system which is

shown diagrammatically in Fig. 1.

The optical system consists of an emitter and sensor, with a lens

in front of each, so arranged that their optical axes cross in the

sampling volume. The emitter, with its lens, produces a narrow

beam of light which is prevented from reaching the sensor by

the bafﬂes. When smoke is present in the sampling volume a

proportion of the light is scattered, some of which reaches the

sensor. For a given type of smoke,

the light reaching the sensor is proportional to the smoke den-

sity. The output from the sensor can be used to activate an

alarm circuit at a pre-determined threshold.

2.2 FEATURES OF MEASURING CHAMBER

In order to make a practical smoke detector which uses the type

of optical system described above, great care is needed in the

design of the housing. Both the optical components and the

sampling volume must be protected from the environment but

still allow smoke to enter freely into the sampling volume. The

housing must also be designed in such a way that dust settling

on its surfaces will not scatter so much light into the sensor that

false alarms are generated.

The emitter is a Gallium Arsenide [GaAs] solid state type op-

erating at a wavelength of 0.94µm; the sensor is a silicon pho-

todiode. These devices with their associated lenses are held

within the optical array which also provides the bafﬂes of

Fig.1. The design of this assembly is such that the presence of

very small insects [e.g. thrips] will not cause false alarms.

Fig. 1 M300 Detector Range, Optical System

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Thorn security MR300 Specifications

General

Brand	Thorn security
Model	MR300
Category	Smoke Alarm
Language	English

Summary

Introduction to MR300 Optical Smoke Detector Range

Operating Principle of MR300 Detectors

Optical System

Details the optical system with emitter, sensor, and lenses crossing optical axes in the sampling volume.

Features of Measuring Chamber

Explains the housing design protecting optics and sampling volume from the environment while allowing smoke entry.

Circuit Operations

Covers general circuit operations, including pulsing emitter and amplifier output proportional to smoke density.

Mechanical Construction of MR300 Detector

Body Assembly

Covers the plastic moulding, contacts, and metallised inner surface for EMI shielding.

Printed Circuit/Optical Array Assembly

Describes mounting of electronic components and optical array on a single PCB for structural integrity.

Final Assembly

Outlines fitting labyrinth mouldings, wire mesh, and the outer cover for the smoke detector.

Technical Specifications of MR300 Series

General Specification

Provides general applicability of specifications across MR300 range variations.

Mechanical Specifications

Details dimensions, materials, and weight of the MR300 detector and base.

Electrical Characteristics

Lists operating voltage, current consumption, stabilization, alarm, and holding currents.

Intrinsic Safety

Specifies compliance with BS 5501 Pt 7 [EN 50 020] for intrinsically safe apparatus.

Performance Characteristics

Defines sensitivity using response threshold value and its relation to smoke colour and obscuration.

Response to Fire Tests

Describes evaluation of detector response to various fire types and sensitivity classification.

Thorn security MR300 User Manual

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