Field Of View; Basic Requirements - Honeywell C7915A Information

C7915A INFRARED FLAME DETECTOR
CAUTION
Electrical Shock Hazard.
Disconnect power supply before beginning installation
to prevent electrical shock and equipment damage;
there may be more than one disconnect.
All wiring must be NEC Class 1 (line voltage).
Use the C7915A only with Honeywell lead sulfide
photocells (part no. 32007255-001) and flame signal
amplifiers specified (see Table 6).
NOTICE
Per industry standards, a conduit seal or a cable type that is
sealed is required to be installed in a device that can result in
flammable gas or flammable liquid flow through a conduit or
cable to an electrical ignition source in the event of a seal
leakage or diaphragm failure.
Proper flame detector installation is the basis of a reliable
flame safeguard installation. Refer to the burner manufacturer
instructions and instructions below. Carefully follow instructions
for the best possible flame detector application.

BASIC REQUIREMENTS

Because all flames produce infrared radiation, a C7915A
Infrared (lead sulfide) Flame Detector can be used to prove the
presence of a flame in a combustion chamber. The detector is
mounted outside the combustion chamber. Screw the
mounting collar to one end of a sight pipe inserted through the
wall of the combustion chamber. The lead sulfide photocell in
the detector sights the flame through the sight pipe.
When a flame is present, the lead sulfide photocell detects the
infrared radiation generated. The C7915A produces an electric
signal that is sent to the amplifier in the flame safeguard
control. The amplified signal pulls in the flame relay in the
flame safeguard control to allow proper operation.
Because it is necessary for the detector to actually see the
flame, it is best to locate the detector as close to the flame as
physical arrangement, temperature, and other restrictions
permit. These restrictions are described in detail below.
DETERMINE THE LOCATION
Before beginning the actual installation, determine the best
location for mounting the flame detector. Carefully consider the
factors discussed in this section before establishing the
location.
TEMPERATURE
The sensitivity of the lead sulfide cell decreases as its
temperature increases. Up to 125°F (52°C), the loss in
sensitivity is negligible, but temperatures above this point
be avoided
. Under normal temperature conditions (below
125°F (52°C), the life of the lead sulfide cell should be
unlimited. The quickest check for excessive temperature is
simply to grasp the detector—it should not be too hot to hold
comfortably in your bare hand.
Several methods are available for cooling the lead sulfide
photocell including ventilating the sight pipe and installing a
pipe nipple, seal-off adapter, and/or heat block between the
sight pipe and the detector. Refer to Installing Accessories,
page 7.
65-0292-06
SIGHTING
The infrared detector must continually sight a stable portion of
the flame being detected. The detector is commonly applied to
detect both the gas pilot and main gas flame, or the gas pilot
and main oil flame.
carefully aimed at the intersection of the pilot and main flame
A Swivel Mount (Honeywell part no. 118367A) is available to
facilitate flame sighting after the C7915A is mounted.

FIELD OF VIEW

A lead sulfide photocell, like other photocells, views an area
rather than a point. It is unable to pinpoint pilot flame location
as easily as a flame rod.
flame, it must view only a part of the flame so it can detect the
pilot only when it is large enough to successfully light the main
burner
. The viewing area must not be so large that a weak and
wavering pilot flame could energize the photocell and cause
the flame relay to pull in.
The area viewed by the photocell depends on:
1. Diameter of the opening in front of the cell.
2. Distance from the cell to the opening.
3. Distance from the opening to the area to be viewed.
Fig. 2 shows three ways of reducing the field of view, assuming
that the distance from the viewing opening to the flame or
refractory cannot be changed. These are (1) lengthening the
sight pipe, (2) reducing the diameter of the sight pipe, and (3)
installing an orifice plate in front of the photocell. Combinations
of these methods can be used.
CHANGING PIPE LENGTH OR SIZE
(DIAMETER)
The effect or changing the length of the sight pipe is shown in
Table 2 and 3.
Changing the diameter of the sight pipe is not as simple as
changing the length, because the C7915A mount and
mounting accessories are all sized for 3/4 in. pipe. When the
sight pipe diameter is reduced, the effect is the same as adding
an orifice plate to the pipe as discussed below.
must
Fig. 2. Methods of reducing C7915A Detector field-of-view.
4
In either case, the detector must be
If the detector is to prove only the pilot
REFRACTORY
DESIRED VIEWING
AREA
UNRESTRICTED VIEW
(1)
BY LENGTHENING
THE SIGHTING PIPE
(2)
BY DECREASING THE
PIPE SIZE (DIAMETER)
(3) BY INSTALLING
AN ORIFICE PLATE
.
M3049C