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C7015A
INSTALLATION
is available to facilitate flame sighting after the
C7015A
is
pipe diameter is reduced, the effect is the same as adding an
mounted.
orifice plate to the pipe as discussed below.
FIELD OF VIEW
A lead sulfide photocell, like other photocells, views an
area rather than a point. It is unable to pinpoint pilot flame
locationaseasilyasaflamerod.Ifthedetectoristoproveonly
the
pilot
jlame,
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) length-
ening the sight pipe, (2) reducing the diameter of the sight
pipe, and (3) installing an orifice plate in front of the photo-
cell. Combinations of these methods can
be
used.
Fig. P-Methods of reducing
C7015A
Detector
field-of-view.
AREA
/M-
0
g/j___------
\
UNRESTRICTED VIEW
3
BY LENGTHENING
THE SIGHT PIPE
CHANGING PIPE LENGTH OR SIZE (DIAMETER)
Theeffectorchangingthelengthofthesightpipeisshown
in Tables 2 and 3.
Changing the diameter of the sight pipe is not as simple as
changing the
length,because
the
C7015A
mount and mount-
ing accessories are all sized for
3/4
in. pipe. When the sight
TABLE 2-DIAMETER OF AREA SIGHTED THROUGH VARIOUS LENGTHS OF
3/4
-IN. PIPE
WITHOUT ORIFICE, IN IN.
Length of
Distance From End of Pipe To Sighted Area-in.
Pip&.
6 12
1
18
1
24
1
30
1
36
I
42
I
48
I
54
I
60
1
66
1
72
7
1.5 2.3 3.1 3.9 4.7 5.5 6.3 7.1
1
8.0 8.7 9.6
10.4
8
1.4 2.1 2.8 3.5 4.2 4.9 5.6 6.3
1
7.1 7.7 8.5
9.1-
TABLE 3-DIAMETER OF AREA SIGHTED THROUGH VARIOUS LENGTHS OF
3/4
IN. PIPE
WITHOUT ORIFICE. IN MM
Length of Distance From End of Pipe To Sighted Area-mm
e
Pipe-mm
152.4
I
304.8
I
457.2
I
609.6
I
762.0
1
914.4
I
1066.8
11219.2
I
1371.6
I
1524.0
11676.4
11828.8
25.4 160.0
1
302.3
1
447.0
1
589.3
1
721.4 876.3
I
Over
1016.0
60-2306-5