7
EN1C-0015SZ20 R0602
IMPORTANT
When installing the detector, make sure it does
not respond to ignition spark.
Single burner requirements
The detector must have an unobstructed view of the flame it
is supervising under all firing conditions. This implies a pro-
per sighting angle and the minimization of screening effects.
Sighting angle
The first 30 percent of a flame (the root) radiates the most
intense ultraviolet energy. The low angle sighting permits the
detector to view a greater depth of the flame root, thus
reducing the effects of irregularities in the flame pattern. The
best sighting angle is nearly parallel to the axis of the flame,
as shown in Figure 3.
NOTE: When possible, it is desirable to tilt the detector and
sight pipe downwards to prefent the build up of soot
in the pipe or on the viewing lens.
In most installations, the detector will need to respond to
the, pilot flame alone, then to the pilot and main burner flame
together and finally to the main burner flame alone. The
detector must meet all sighting requirements which apply:
1. Pilot flame alone - the smallest pilot flame that can be
detected must be capable of reliable ignition the main
burner.
2. Pilot and main burner flame together - the detector must
sight the junction of both flames.
3. Main burner flame alone - the detector must sight the most
stable part of the flame for all firing rates
Screening effects
Smoke, fuel mist, dirt and dust are masking agents that
absorb ultraviolet radiation from the flame. They create a
screen that reduces the amount of ultraviolet radiation
reaching the detector and may cause flame signal
deterioration resulting in a shutdown. The adverse affects of
Screening may be minimized by proper burner adjustment,
increasing the detector viewing area (shorten sight pipe and/
or increase its diameter).
Multifuel requirements
In addition to meeting the requirements for a single burner, a
multiburner installation also requires flame discrimination.
Flame discrimination may be defined as the location of all
flame detectors such that each detector responds only to
the flame(s) produced by the burner it is supervising.
Multiburner requirements
In multiple burner systems, not every detector can be
positioned so its line of sight does not intercept flames from
other burners. This situation occurs in front-fired boiler
furnaces having more than one row of burners, or in multilevel
opposed-fired furnaces where the burners face each other.
When planning such an installation, locate each flame
detector so that it has the best possible view of the root of
the flame(s) it is supervising and the worse possible view of
all other flames.
Figure 4. illustrates a critical detector application Problem
requiring flame discrimination. Flame discrimination is
accomplished by detector 1 by reducing its sensitivity until
the flame relay (in the flame safeguard control) does not
respond to flame 2. Note that detector 1 is aimed at the root
of Flame 1 where UV (ultraviolet) energy is most intensive.
Although it sights flame 2 is not aimed at the root of flame 2.
The sensitivity of detector 1 is reduced to a point that ensures
maximum sensitivity to flame 1 while rejecting flame 2.
similarly, detector 2 is adjusted to ensure maximum sensitivity
to flame 2 while rejecting flame 1.
If the sensitivity control on a detector is set at its minimum
position and flame discrimination cannot be achieved, insert
an orifice plate in the sight pipe. An orifice of the proper
diameter will reduce the ultraviolet radiation reaching the
detector so that the sensitivity can be adjusted to effect flame
discrimination.
Parallel flame detectors
Two C7061A/F detectors can be connected in parallel to the
same flame signal amplifier and still provide independent
sensitivity adjustment. This capability is particular useful for
multiburner, multifuel applications.
Shifting flame patterns, commonly encountered on burners
with wide turndown ratios, may require parallel detectors to
prove the flame at the highest and lowest firing rates. In this
case, one detector supervises the pilot (interrupted) and both
detectors supervise the main burner flame. During the main
burner “run” period, either detector is capable of maintaining
system operation.
In addition to assuring more reliable flame detection, parallel
detectors facilitate maintenance during burner operation.
Each detector can be removed in turn without shutting down
the supervised burner. However, a flame simulating failure
occurring in the flame signal amplifier or in either detector
will cause a shutdown.
Fig. 3. Sighting angle
Fig. 4. Critical detector application problem
Содержание C7061A
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