CB780/CB784 RELAY MODULES
33
32-00207—01
Hot Refractory Hold-in Test (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.
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 multi-fuel
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
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 Burner 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) are 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 resighting
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 hold-in 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 shut-off
valve(s).
2.
Start the burner and use the Run/Test Switch 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.
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
check for proper detector operation, check the Flame
Failure Response Time (FFRT) and conduct Safety
Shutdown Tests under all operating conditions.
Flame Signal With Hot Combustion
Chamber (All Installations)
With all initial start-up tests and burner adjustments
completed, operate the burner until the combustion
chamber is at the maximum expected temperature.
Observe the equipment manufacturer warm-up
instructions. Recycle the burner under these hot
conditions and measure the flame signal. Check the pilot
alone, the main burner flame alone, and both together
(unless monitoring only the main burner flame when
using DSI). Check the signal at both High and Low Firing
Rate positions and while modulating, if applicable.
If the flame signal is too low or unsteady, check the flame
detector temperature. Relocate the detector if the
temperature is too high. If necessary, realign the sighting
to obtain the proper signal and response time. If the
response time is still too slow, replace the Plug-in Flame
Signal Amplifier. If the detector is relocated or resighted, or
the amplifier is replaced, repeat all required Checkout
tests.Check the FFRT of the Flame Amplifier. Lower the set
point of the operating controller and observe the time it
takes for the burner flame to go out. This should be within
3 seconds maximum.
Safety Shutdown Tests (All
Installations)
Perform these tests at the end of Checkout, after all other
tests have been completed. If used, the external alarm
should turn on. Press the CB780/CB784 reset pushbutton
to restart the system.