Honeywell 7800 Series Installation Instructions Manual page 37

a. 6000V systems—1/16 to 3/32 in. (1.6 to 2.4 mm).
b. 10,000V systems—1/8 in. (3.2 mm).
4. Make sure the leadwires from the flame rod and
ignition electrode are not too close together.
5. Replace any deteriorated leadwires.
6. If the problem cannot be eliminated, the system may
have to be changed to an ultraviolet flame detection
system.
Hot Refractory Saturation Test (All
Infrared Detectors)
Test to make certain that radiation from hot refractory
does not mask the flickering radiation of the flame itself.
Start the burner and monitor the flame signal during the
warmup period. A decrease in signal strength as the
refractory heats up indicates hot refractory saturation. If
saturation is extreme, the flame signal will drop below
1.25 Vdc and the system will shut down as though a flame
failure occurred.
If hot refractory saturation occurs, the condition must be
corrected. Add an orifice plate in front of the cell to restrict
the viewing area, try to lengthen the sight pipe or decrease
the pipe size (diameter). Continue adjustments until hot
refractory saturation is eliminated.
Hot Refactory Hold-in Test
(Rectifying Photocell or All Infrared
Detectors)
Test to make certain hot refractory will not delay the flame
detection system response to a flameout. This condition
can delay response to flame failure and also can prevent a
system restart as long as hot refractory is detected.
To check rectifying photocells for hot refractory holdin,
operate the burner until the refractory reaches its
maximum temperature. Then terminate the firing cycle by
lowering the set point of the operating controller, or
setting the Fuel Selector Switch to OFF. Do not open the
master switch. Visually observe when the burner flame or
FLAME LED goes out. If this takes more than .8 or 3
seconds (depending on the FFRT of the amplifier), the
photocell is sensing hot refractory. This condition must be
corrected as described in the last paragraph of this test.
Infrared (lead sulfide) detectors can respond to infrared
rays emitted by a hot refractory, even when the refractory
has visibly ceased to glow. Infrared radiation from a hot
refractory is steady, but radiation from a flame has a
flickering characteristic. The infrared detection system
responds only to flickering infrared radiation; it can reject
a steady signal from hot refractory. The refractory steady
signal can be made to fluctuate if it is reflected, bent or
blocked by smoke or fuel mist within the combustion
chamber. Be careful when applying an infrared system to
verify its response to flame only.
To check infrared (lead sulfide) detectors for hot refractory
hold-in, operate the burner until the refractory reaches its
maximum temperature. If the installation has a multifuel
burner, burn the heavier fuel that is most likely to reflect,
bend or obscure the hot refractory steady infrared
radiation. When the maximum refractory temperature is
RM7888A 7800 SERIES RELAY MODULE
reached, close all manual fuel shutoff valve(s), or open the
electrical circuits of all automatic fuel valve(s). Visually
observe when the burner flame or FLAME LED goes out. If
this takes more than three seconds, the infrared detector
is sensing hot refractory. Immediately terminate the firing
cycle. (Lower the set point to the operating controller, or
set the Fuel Selector Switch to OFF. Do not open the
master switch.)
NOTE: Some burners continue to purge oil lines between
the valve(s) and nozzle(s) even though the fuel
valve(s) is closed. Terminating the firing cycle
(instead of opening the master switch) will allow
purging the combustion chamber. This will
reduce a buildup of fuel vapors in the combustion
chamber caused by oil line purging.
If the detector is sensing hot refractory, the condition
must be corrected. Add an orifice plate in front of the cell
to restrict the viewing area of the detector. If this does not
correct the problem, resight the detector at a cooler, more
distant part of the combustion chamber. While re-sighting
the detector, be aware that it must also properly sight the
flame. For an infrared detector, try lengthening the sight
pipe or decreasing the pipe size (diameter). For details,
refer to the detector Instructions and the equipment
Operating Manual. Continue adjustments until hot
refractory holdin is eliminated.
Ultraviolet Sensor, Ignition Spark
Response Test (All Ultraviolet
Detectors)
Test to make certain that the ignition spark is not
actuating the FLAME LED:
1. Close the pilot and main burner manual fuel shutoff
valve(s).
2. Start the burner and energize Special Function 1
(terminal 6) only to stop the sequence in the PILOT
IGN period. Ignition spark should occur, but the
flame signal should not be more than 0.5 Vdc.
3. If the flame signal is higher than 0.5 Vdc and the
FLAME LED does come on, consult the equipment
operating manual and resight the detector farther
out from the spark, or away from possible reflection.
It may be necessary to construct a barrier to block
the ignition spark from the detector view. Continue
adjustments until the flame signal due to ignition
spark is less than 0.5 Vdc.
NOTE: The Honeywell Q624A Solid State Spark Genera-
tor will prevent detection of ignition spark when
properly applied with the C7027, C7035 or C7044
Minipeeper Ultraviolet Flame Detectors or the
C7061 Self check Ultraviolet Flame Detector. The
Q624A is only for use with gas pilots.
Response to Other Ultraviolet
Sources
Some sources of artificial light, such as incandescent or
fluorescent bulbs, mercury, sodium vapor lamps and
daylight, produce small amounts of ultraviolet radiation.
Under certain conditions, an ultraviolet detector will
respond to these sources as if it is sensing a flame. To
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