C7076A,D ADJUSTABLE SENSITIVITY ULTRAVIOLET FLAME DETECTORS
• the surface represents a significant percentage of the
detector field of view.
If the temperature or a radiant surface causes the flame relay
(in the flame safeguard control) to pull in, re-aim the sight pipe
so the detector views a cooler area, or decreases the
sensitivity of the detector.
Ignition spark is a rich source of ultraviolet radiation. When
installing the detector, make sure it does not respond to
Single Burner Requirements
The detector must have an unobstructed view of the flame it is
supervising under all firing conditions. This implies a proper
sighting angle and the minimization of screening effects.
The first 30 percent of a flame (the root) radiates the most
intense ultraviolet energy. 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 Fig. 3.
DETECTOR IN GOOD
(LOW ANGLE SIGHTING)
Fig. 3. 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 lens.
In most installations, the detector will need to respond to the
pilot flame alone, then to the pilot flame 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 reliably lighting the main
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.
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
DETECTOR IN POOR
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), and optimizing detector
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.
In multiple burner systems, not every detector can be
positioned so that 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 first 30
percent closest to the burner nozzle (the flame root) it is
supervising, and the worst possible view of all other flames.
Fig. 4 illustrates a critical detector application problem that
requires flame discrimination. Flame discrimination is
accomplished for Detector A by repositioning it until the flame
relay (in the flame safeguard control) does not respond to
Flame B. Note that Detector A is aimed at the first 30 percent
of Flame A where the ultraviolet radiation is most intense. It
sights the tip of Flame B, but it is not aimed at the first 30
percent of Flame B where ultraviolet radiation is intense.
Detector A is repositioned to assure maximum response to
Flame A while rejecting Flame B. Similarly, Detector B is
positioned to assure maximum response to Flame B while
rejecting Flame A.
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
Fig. 4. Example of flame discrimination problem