IRIS S550, Applications Manual, Page: 7 / 19

The cable wiring on the other end going to the
signal processor is easier to do. The cable should
be prepared in a similar way to the plug end
particu larly the shield from the WHT wire. Make
sure the shield doesn't touch the other terminals.
SIGHT ING OF VIEW ING HEAD
The sighting of the viewing head should be
parallel to the cen terline of the burner in the
direction of the flame. The sight pipe should be
mounted as close to the cen terline as possible; the
idea is to sight along the flame rather than across
the flame. This will help prevent drop outs of the
flame under changing load condi tions.
Utilizing a sighting or the sight pipe aimed at the
root of the flame (where the turbulent combustion
air mixes with the flame) is a good starting point
for optimizing the sighting. Using a swivel mount
to “zero-in” on the highest signal will assure
maximum performance. Make sure the diameter
of this sight pipe is large enough to allow a
reasonable field of view. The S550’s has two
angles of view, one for the IR detector, which is
1.0
°
and one for the UV detector which is about
3.0
°;
this trans lates into a circle of view that
varies with the viewing distance as shown in the
following table.
Dis tance Dis tance
Di ame ter of
IR view
Di ame ter of
UV view
ft inches inches inches
2 24 .64 1.3
3 36 .73 1.9
6 72 1.45 3.8
12 144 2.90 7.6
18 216 4.35 11.4
Detecting flame in a sulfur recovery unit can
present problems for flicker type flame monitors
such as the IR detector in the S550 viewing head.
The IR detector will detect natural gas used for the
warm-up of the reactor. Usually the combustion
air is turbulent enough to cause a good flicker
signal. When the sour gas is intro duced and the
natural gas shut down the flame signal may drop
off or drop out entirely. The reason for this is that
there is a complete change in the flicker content
for the existing viewing head sighting. If this is the
case, then one should try and optimize the flame
signal for the sour gas by “zeroing-in” on this
flame, not the warm-up burner.
After optimizing the sighting for the sour gas one
may find that the signal level is too low on the
natural gas. One should then try the UV detector
for this appli cation. It may be necessary to use two
sets of set points for flame ON and flame OFF, one
set for proving and detecting the natural gas flame
and the other for proving and detecting the sour
gas flame. The switch-over from Channel A to
Channel B should be done when removing the
natural gas burner. This can be imple mented from
the burner control system. This switch-over and
the use of Channels A and B with their
independent settings is explained in the section
ASSIGNING DIFFERENT S550 SETTINGS TO
CHANNEL A and B
on page 9.
IR DETECTOR
The IR detector responds to the flicker content in
the flame. Flame flicker is caused by the
combustion, or forced air injected into the flame.
This combustion air can be mixed with the fuel
(pulverized coal) or can be intro duced separately.
In either case, forced air at high velocity is intro
-
duced in such a way as to aid the combustion
process. This air is usually made turbulent by
causing it to swirl with spin vanes located in the
burner barrel.
Flame flicker is created when this turbulent air
mixes with the flame. It is composed of random
frequencies from zero Hz to over 2,000 Hz. The
amount of high frequency flicker (above 200 Hz)
is dependent on the fuel and burner. The amplitude
of the flicker frequencies always follows an
exponential curve with zero frequency having the
highest amplitude and the higher frequencies the
lowest. The amplitude level of the higher
frequencies is usually 40dB down (factor of 100)
from zero Hz or DC.
PAGE 7
IRIS MODEL S550 APPLICATION MANUAL