C7061M MINIATURE DYNAMIC SELF-CHECK ULTRAVIOLET FLAME DETECTOR
65-0304—05
4
Because it is necessary for the UV sensing tube 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 in the
following paragraphs.
Determine Location
Before beginning the actual installation, determine the best
location for mounting the detector. Carefully consider the
factors discussed in this section before deciding on the
location.
Temperature
Install the C7061 where the ambient temperature (outside the
case) stays within the ambient operating temperature ratings.
To keep the C7061 below its maximum rating, it may be
necessary to add additional insulation between the wall of the
combustion chamber and the detector. A shield or screen can
be added to reflect radiated heat away from the detector. If the
detector continues to get too hot, cooling is necessary. Refer to
the Sight Pipe Ventilation section.
Vibration
The detector withstands normal burner vibration. If the C7061
is subject to excessive vibration, use a special 123539
Antivibration Mount. If you use this mount, install it before you
position and sight the detector.
Clearance
Make sure there is enough room to easily mount the sight pipe,
detector, and all required fittings, and to remove the detector
for troubleshooting and servicing.
Radiation Sources (Other than
Flame)
Examples of radiation sources (other than flame) that could
actuate the detection system:
1.
Ultraviolet Sources:
a. Hot refractory above 2500°F (1371°C).
b. Spark:
c. Ignition transformers.
d. Welding arcs.
e. Lightning.
f. Gas lasers.
g. Sun lamps.
h. Germicidal lamps.
2.
Gamma Ray and X-ray Sources:
a. Diffraction analyzers.
b. Electron microscopes.
c. Radiographic X-ray machines.
d. High voltage vacuum switches.
e. High voltage condensers.
f. Radioisotopes.
Except under unusual circumstances, none of these sources
except hot refractory and ignition spark would be present in or
near the combustion chamber.
The detector can respond to hot refractory above 2300°F
(1260°C) if the refractory surface represents a significant
percentage of the detector field of view. If the temperature of
the hot refractory causes the flame relay (in the flame
safeguard control) to pull in, re-aim the sight pipe so the
detector views a cooler area of the refractory.
Ignition spark is an intense source of ultraviolet radiation.
When installing the detector, make sure it does not respond to
ignition spark by following the Ignition Spark Response Test
listed on page 9.
Single Burner Requirements
The detector must have an unobstructed view of a steady part
of the flame it is supervising. This requires a proper sighting
angle and minimized ultraviolet radiation attenuation effects.
However, when supervising only one burner, sighting
requirements are simplified.
Sighting Angle
The first 30 percent of a flame closest to the burner nozzle (the
flame root) emits the most ultraviolet energy. Also, if the
detector sights the flame at an angle instead of
perpendicularly, it views more flame depth. Therefore, the best
sighting angle is nearly parallel to the axis of the flame,
permitting the detector to view a large portion of the first 30
percent of the flame closest to the burner nozzle, as illustrated
Low angle sighting permits the detector to view a greater depth
of flame, thus reducing the effects of instabilities in the flame
pattern. Also, the environment near the burner nozzle is
usually cleaner than at any other part of the combustion
chamber. This provides a clearer line of sight and can keep the
viewing window cleaner, thus reducing the maintenance
required.
Fig. 2. Detector sighting angle.
NOTE: When possible, it is desirable to tilt the detector
and sight pipe downward to prevent the buildup
of soot in the pipe or on the viewing window.
In most installations, the detector needs to respond to the pilot
flame alone, then the pilot and main burner flame together, and
finally the main burner flame alone. The detector must meet all
sighting requirements that apply:
• Pilot flame alone—the smallest pilot flame that can be
detected must be capable of reliably igniting the main
burner.
• Pilot and main burner flame together—the detector must
sight the junction of both flames.
• Main burner flame alone—the detector must sight the most
stable part of the flame for all firing rates.
M29115A
UNBURNT FUEL
GOOD
DEPTH OF FLAME IS LONG WHEN THE
MONITORING DIRECTION INTERSECTS
THE FLAME AXIS AT ACUTE ANGLE
BURNER
BAD
DEPTH OF FLAME IS SHORT
