Over - Honeywell C7915A Information

C7915A INFRARED FLAME DETECTOR
PILOT HOT REFRACTORY
Fig. 3. Using orifice plate to restrict detector field of view to intersection of pilot and main flame,
RESPONSE TO HOT REFRACTORY
Although the infrared amplifier will not respond to steady
radiation, as produced by hot refractory, be careful to protect
the infrared detector from hot refractory radiation because of
shimmer
two possible conditions,
a. Shimmer—Turbulent hot air, steam, smoke, or fuel
spray in the combustion chamber can reflect, bend,
or block the steady infrared radiation emitted by a hot
refractory. These conditions can change the steady
radiation from a hot refractory into a fluctuating radia-
tion. If these fluctuations occur at the same fre-
quency as that of a flickering flame, they will simulate
flame and will hold in the flame relay after the actual
burner flame has been extinguished.
b. Radiation saturation—Steady hot refractory radiation
can become strong enough to mask the fluctuating
radiation of the flame. This is similar to the effect of
holding up a candle in front of the sun—the light of
the sun is so strong that the candle light cannot be
seen. If radiation saturation is extreme, the flame
relay will drop out, and the system will shut down as
though a flame failure has occurred.
Both of these problems will be minimized by aiming the
detector at a portion of the refractory that is:
• as cool as possible.
• as far from the cell as possible.
• as reduced a field of view as possible, see Fig. 2 and 3.
Refractory temperatures in the combustion chamber will vary
with combustion chamber design, but generally the end wall of
the chamber will be the hottest point. It will normally be best to
aim the detector at the side wall of the refractory (Fig. 4), at a
point above the refractory (Fig. 5), or at the floor of the
combustion chamber (Fig. 6).
65-0292-06
WITHOUT ORIFICE PLATE
MAIN FLAME
or to small area of hot refractory.
radiation saturation
and
WITH ORIFICE PLATE
PILOT HOT REFRACTORY
SIGHTING SUMMARY
When sighting the detector, two important factors to consider
are: (1) proper sighting of the flame being detected (normally
the pilot/main flame junction), and (2) avoiding hot refractory
. sighting.
A typical sighting arrangement is shown in Fig. 4. The detector
is aimed at the intersection of the pilot and main flames, and at
a relatively cool side of the combustion chamber. The detector,
in this case, would be located as close as possible to the
burner to sight the maximum depth of the flame and reduce the
effect of variations in the main flame pattern.
The detector can also be sighted from a point below and close
to the burner with the line-of-sight above the refractory (Fig. 5).
The third method is to aim the detector from above the burner,
sighting a portion of the refractory floor (Fig. 6). This type of
application requires that the pilot flame be carefully sighted
from the side. The detector should not be sighted
shoulder
of the pilot because the chances increase of sighting
a pilot too small to satisfactorily light the main flame.
The actual area of hot refractory sighted should be as small as
possible and consistent with proper sighting of the flame. Refer
to Fig. 2 and 3 for methods of reducing the area of hot
refractory sighted.
6
MAIN FLAME
M3050B
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