Honeywell 7800 Series Manual page 27

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 or infrared flame
detection system.
HOT REFRACTORY SATURATION TEST (All
Infrared Detectors)
Test to be sure 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 has 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 adjust-
ments until hot refractory saturation is eliminated.
HOT REFRACTORY HOLD-IN TEST
(Rectifying Photocell or All Infrared Detectors)
Test to be sure 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 hold-
in, 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 longer 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 infra-
red 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 refrac-
tory 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 refrac-
tory reaches its maximum temperature. If the installa-
tion has a multi-fuel burner, burn the heaviest fuel that
is most likely to reflect, bend or obscure the hot refrac-
tory steady infrared radiation. When the maximum
refractory temperature is 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 sens-
ing 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 (in-
stead of opening the master switch) will allow purg-
ing of 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 resighting
the detector, be aware that it must also properly sight the
flame. When using infrared detector, try lengthening the
sight pipe or decreasing the pipe size (diameter). For
details, refer to the detector Instructions and the equip-
ment Operating Manual. Continue adjustments until hot
refractory hold-in is eliminated.
ULTRAVIOLET SENSOR, IGNITION SPARK
RESPONSE TEST (All Ultraviolet Detectors)
Test to be sure 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 run through the PILOT IGN
period. Ignition spark should occur, but the flame signal
should not be more than 0.5 Vdc and the FLAME LED
should not turn on.
3. If the flame signal is higher than 0.5 Vdc and the
FLAME LED does come on, consult the equipment Oper-
ating Manual and resight the detector further 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 prop-
erly applied with the C7027, C7035 or C7044
Minipeeper Ultraviolet Flame Detectors. The Q624A is
only for use with gas pilots.
RESPONSE TO OTHER ULTRAVIOLET SOURCES
Under certain conditions, an ultraviolet detector will
respond to other ultraviolet sources as if it is sensing a flame.
These ultraviolet sources include artificial light, such as
incandescent or fluorescent bulbs, mercury and sodium
vapor lamps or daylight. To check for proper detector
operation, check the Flame Failure Response Time (FFRT)
and conduct Safety Shutdown tests under all operating
conditions.
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RM7895A,B,C,D
CHECKOUT
65-0086—2