Product application & Design information Doc. version 1.0 14 February 2012
3
FC400CH Addressable carbon mo heat detector
2.3.2 HEAT
Refer to Fig. 3.
The negative temperature coefficient thermistor produces an analogue output
which is fed to an analogue input on the communications interface.
2.4
COMMON CIRCUIT
Refer to Fig. 3.
Communications between the controller and detector uses the Frequency Shift
Keying (FSK) method. The ‘Discrimination Circuit’ filters the FSK signal from the
+ve line voltage and converts it to a digital square wave input for the ‘Communica-
tions ASIC’.The ‘Communications ASIC’ decodes the signal and when its own ad-
dress is decoded, the analogue inputs received from the carbon monoxide and
heat sensing elements are converted to corresponding digital values. These digital
values are then passed to the ‘Tx Driver Circuit/Current Sink’ which converts them
to FSK signals and applies them to the +ve line for transmission to the controller.
The Common Circuit is also used to:
Ø
Control Sounder and Relay bases via the ‘Functional Base Interface Circuit’
from controller commands.
Ø
Control the operation of the Remote LED via the ‘Remote LED Circuit’ from con-
troller commands.
2.5
WIRING
Loop cabling is connected to base terminals L (-ve) and L1 (+ve). A drive is pro-
vided for a remote indicator connected between loop positive and terminal R. Ter-
minal L2 (FUNCTIONAL BASE output) is for use with functional sounder base.
3.
MECHANICAL CONSTRUCTION
The major components of the detector are:
Ø
Body Assembly
Ø
Printed Circuit
Ø
CO Cell
Ø
Screening Can
Ø
CO Closure
Ø
Thermistor
Ø
Light Pipe
Ø
Outer Cover
3.1
BODY ASSEMBLY
The body assembly consists of a plastic moulding which has four embedded de-
tector contacts which align with contacts in the base.The moulding incorporates
securing features to retain the detector in the base.
The CO cell is inserted onto the PCB followed by the screening can.
Four PCB mounted spring contacts provide electrical connection between the de-
tector contacts and the PCB.
The light pipe is slotted into the CO closure which is then clipped to the body. Fi-
nally, the outer cover is clipped to the body.
1.
INTRODUCTION
The FC400CH carbon monoxide plus heat detector forms part of the 400 Series Ad-
dressable Fire detectors.
The detector is intended to plug into the following:
Ø
5B 5” Universal Base.
Ø
FC450IB 5” Isolator Base.
Ø
FC430SB Low Power Sounder Base.
The detector is designed to transmit, to a remote FireClass fire controller, digital
signals which represent status of the carbon monoxide and heat elements of the
detector.
Software within the controller is used to interpret the returned carbon monoxide
and heat values to raise alarm or other appropriate response according to the type
of detector configured in FireClass Console.
The mode of the detector may be:
§
Heat only detector (A1R or A2S).
§
Carbon monoxide only detector (sensitivity: High, Normal or Low).
§
Compensated carbon monoxide detector (sensitivity: High, Normal or Low).
§
Compensated carbon monoxide (sensitivity: High or Normal) combined with
heat (A1R).
+
Note:
Ø
The heat detection grades are to EN54-5.
Ø
Normal and High sensitivity settings have been approved by the Loss Preven-
tion Council Board.
1.1
DAY/NIGHT SWITCHING
Two modes of detector operation are selectable from the list of possible modes as
follows:
Ø
‘Normal’ mode, ie night time operation in which the detector will be evaluated
most of the time.
Ø
‘Day’ mode in which the detector can be switched under certain circumstances,
eg during daytime when the building is occupied with people being able to de-
tect a fire manually. Switching to the ‘daytime’ mode can be done either by or
time driven.
1.3
SENSITIVITY SWITCHING
In addition to mode switching, the sensitivity can be changed within the actual
mode.This can be done either by PC programming or be time driven (eg,
day/night switching). Changing the sensitivity is done by shifting the sensitivity
up or down.
2.
OPERATING PRINCIPLE
2.1
CARBON MONOXIDE
2.1.1 SENSING CELL
The CO element of the detector uses an electrochemical cell to detect the build up
of carbon monoxide generated by fires. The cell operates by oxidising carbon
monoxide on a platinum sensing electrode. Whilst on a corresponding counter
electrode the reduction half of the reaction takes place. The Sensing Cell is repre-
sented diagrammatically in Fig. 2.
When this reaction takes place the potential across the cell tries to change and this
causes a current to flow within the circuit around the cell. The current is mirrored
into a current to voltage conversion circuit with the resulting output directly propor-
tional to the carbon monoxide concentration.
The cell itself has a diffusion limiting component to ensure that all carbon monox-
ide in the area proximate to the sensing electrode is continuously oxidised. This
means that the rate of transport of carbon monoxide to the cell is directly propor-
tional to the external concentration and independent of air-speed.
2.2
HEAT DETECTOR
The heat element of the detector uses a single thermistor to produce an output propor-
tional to temperature. Rate of change of temperature is determined by the controller by
using differences between consecutive temperature values returned to the controller.
2.3
CIRCUIT DESCRIPTIONS
2.3.1 CARBON MONOXIDE
Refer to Fig.3.
The current through the cell circuit is added to a fixed baseline voltage and mir-
rored by the current mirror. This is fed to a current to voltage converter amplifier
which buffers and scales the signal. The resultant voltage is fed to an analogue in-
put on the common circuit.
ENGLISH
FC400CH Addressable Carbon Mo Heat Detector
FIG.1
