System Design

Engineers familiar with codes of practice for hazardous area systems should only undertake the design of an intrinsically safe fire detection system. In Europe the standard is EN 50014, Electrical apparatus for potentially explosive atmospheres – General requirements. The fire detector performance is the same as the standard none intrinsically safe counterparts. Performance information given in standard product guides is therefore applicable to the intrinsically safe range. The BASEEFA certification of the intrinsically devices covers their characteristics as components of an intrinsically safe system. This indicates that the flame detectors can be used with a margin of safety in such systems. In safe area (standard) applications it is some times desirable to connect the wiring as a loop, with both ends terminated at the control panel. In the event of an open-circuit fault it is then possible to drive both ends simultaneously. In a hazardous area it is not possible to use a loop configuration because the potential to feed power from each end of the loop would double the available energy in the hazardous area and contravene the energy limitations of the intrinsically safe certification. All circuits must therefore be connected as spars from the safe area or as radial connections from the control panel.

Technical Data

Mechanical Housing Material: Die Cast Zinc alloy
See figure 2 FIRE Housing Colour: Blue (typical)
IR SENSOR Housing Dimension: Height = 142mm Width = 108mm Depth = 82mm Fig. 2
(Excluding Mounts) The flame detectors respond to light emitted from flames during combustion. The detectors discriminate between flames and other light sources by responding only to low frequency flickering produced by flames (typically 1 to 15Hz). The detectors ignore fixed light sources and rapidly flickering illumination predominantly produced by lighting. The flame flicker techniques have the advantage of still allowing the detection of flames through a thin layer of oil, water vapour, ice or dust. This makes these detectors particularly useful in industrial applications. Full details of the principles of operation, electrical description, and other detailed technical data are published in the products individual data sheet. Cable gland Entries: 2 X 20mm Electrical Supply In: Voltage Current
Terminals 1(+) & 2(-) 14 to 30Vdc 2 to 30mA
See data sheet for detail Polarity sensitive Optional Input: Voltage Current 14 to 30Vdc 40µA
typ. @ 24V IN
Polarity sensitive Terminals 3(+) & 4(-)

Types of Safety Barrier

Optional Output: Voltage Current
Terminals 3(+) & 4(-) The system configuration can for three types of safety barrier, each of which has its own advantages and disadvantages. A brief outline of the characteristics is given below. 0V to
Supply In (O/C) 2.4
mA typ .
Internally Limited Single Channel 28V/300 Barrier This is the most basic type of barrier and therefore the lowest cost. Being passive devices, they also impose the minimum of restrictions on the operation of the flame detectors. Thus, single channel barriers are available either as positive or negative polarity where the polarity refers to the polarity of the applied voltage Star-connected A.C. Barrier Optional Relays Contact Ratings: Voltage Current 30Vdc. Max. 1 Amp. Max. A.C. barriers are also passive devices and must still be connected to a high-integrity safety earth. However, they are designed to allow either positive or negative voltages with respect to earth and under normal conditions provide a connection to earth via a reverse-diode, rather than directly. The disadvantage of this type of barrier is that the end-to-end resistance is nominally 1200ohms compared with the 300 ohms of the single channel type. This high resistance results in an extra voltage drop in the circuit. This type of barrier is not recommended for general use.
Resistive Loads Only Terminals 3 to 8 relative to earth . The significance of this is that one side of the barrier must be connected to a high-integrity (safety) earth. Environmental Operating Ambient Temperature: -20°C to +40°C(T4) -20°C to +85°C(T3) Although this connection has no effect on the operation of the flame detector and is not needed for their correct operation, it may not be acceptable to the operation of the control and indicating equipment. This is particularly true if the control equipment incorporates earth-leakage monitoring and even without this feature the earthing of the loop may cause unwanted cross-talk between loops. If the earth connection is not acceptable then the A.C. or isolating barriers should be used.
Check detector limits ATEX Approval Category

II 1 G

CENELEC / IEC Marking

EEx ia IIC T4

Apparatus Certificate Number BAS02ATEX1001 6 7