Siemens Flame Detector, Three Infrared Sensors, ASAtechnology, IP67 FDF241-9

Overview

Smoke and heat detectors wait for a fire to grow. A flame detector looks for the flame itself, which matters where a fire can start fast and burn clean, such as with flammable liquids or gas.

This Siemens unit watches for flames across a space rather than at a single point. It can report as an individually addressed device or on a collective detector line, so it suits both types of fire alarm system.

How it works

• Sensor A: a pyroelectric sensor that reads the infrared radiation of hot CO 2, the signature of a flame, between 4.0 and 4.8 µm.
• Sensor B: a second pyroelectric sensor tuned to hot objects, so a warm surface is not taken for a flame.
• Sensor C: a silicon photo diode that watches sunlight, so the detector can allow for it.
• Fuzzy logic and wavelet analysis: the detector compares the three signals at the same time to judge whether a real fire is present. An additional emergency activation channel guards against a possible decision emergency.

Where to use it

It is suited to spaces where sunlight or hot motors could confuse a simpler detector. Typical sites include power plants, transformer stations, print shops, wood storage and motor test beds.

Larger spaces suit it too: atriums, malls, hangars for military and civil aircrafts and subway tunnels. With DNV GL (marine) approval, it also suits ferries, cargo vessels and marine machine rooms.

What the figures mean in practice

• DC 12…33 V addressed: the voltage range on an FDnet/C-NET line. On a collective line the range is DC 14…28 V.
• 0.7 mA in quiet state: the detector's standing draw when addressed, 0.5 mA when collective. Add it to the line calculation with every other device.
• -35…+70 °C: the operating range, wide enough for unheated stores and outdoor plant.
• IP67: dust tight and protected against temporary immersion in water.

Installing it

• Fixing: mount the base on a stable, vibration-free surface. Fit the detector only once the installation has been checked, just before commissioning.
• Aiming: the MV1 bracket holds the detector at 45° for room monitoring, and the MWV1 ball and socket joint aligns it accurately to an area.
• Cable entry: six M20 threads take cable glands, and an M20 x 1.5 metal cable gland has its own order number. Fire-resistant cable is the usual choice for fire alarm circuits.
• Outdoors: plan a rain hood for exposed positions. One is plastic (ABS) and one stainless steel.

Planning your system

Each detector needs an FDFB291 base, plus a bracket or rain hood where the position calls for one.

Flame detection usually sits alongside smoke and heat detectors in a wider fire alarm system, each covering the risks it suits. The commercial fire alarm guide explains how an addressable system differs from a conventional one.

As a rule, have a competent person design and commission any change to a fire alarm system.

Standards and ratings explained

• EN 54-10: the European standard for flame detectors.
• EN 54-17: the standard for short-circuit isolators. The detector includes one, so a fault on the line can be isolated between two devices.
• LPCB and VdS: independent certification bodies for fire products.