Honeywell 7800 Series Manual page 26

RM7885A
CHECKOUT
10. Restart the system and increase the pilot flame size
by increasing its fuel flow until a smooth main flame is
accomplished.
11. Observe the flame signal voltage. It should be ap-
proximately 1.25-1.50 Vdc. Reposition the flame scanner
sight tube or use orifices until the pilot flame signal voltage
is approximately 1.25-1.50 Vdc.
12. When the main burner lights reliably with the pilot at
turndown, disconnect the manometer (or pressure gauge)
and turn the pilot gas flow up to that recommended by the
equipment manufacturer.
13. If used, remove the bypass jumpers from the subbase
terminals, limits/control or switches.
14. Run the system through another cycle to check for
normal operation.
15. Return the system to normal operation.
IGNITION INTERFERENCE TEST
(ALL FLAME RODS)
Test to be sure that a false signal from a spark ignition
system is not superimposed on the flame signal.
Ignition interference can subtract from (decrease) or
add to (increase) the flame signal. If it decreases the flame
signal enough, the RM7885 will not recognize a flame. If
it increases the flame signal, it could cause the FLAME
LED to come on when the true flame signal is below the
minimum acceptable value.
Shut the manual main fuel valve. Press the Start Switch
and measure the flame signal with both ignition and pilot
on. Then release the Start Switch and measure the pilot
flame only. Any significant difference (greater than .5
Vdc) indicates ignition interference.
Open the manual main fuel valve when ignition inter-
ference is or has been reduced to less than .5 Vdc.
TO ELIMINATE IGNITION INTERFERENCE
1. Make sure there is enough ground area.
2. Be sure the ignition electrode and the flame rod are
on opposite sides of the ground area.
3. Check for correct spacing on the ignition electrode:
a. 6,000V 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 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
warm-up 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. You can also try to lengthen the
sight pipe or decrease the pipe size (diameter). Continue
adjustments until you eliminate hot refractory saturation.
HOT REFRACTORY HOLD-IN TEST (RECTIFY-
ING PHOTOCELL OR ALL INFRARED DETEC-
TORS)
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
pressing the Stop Switch. 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 (depend-
ing on the FFRT of the amplifier), the photocell is sensing
hot refractory. This condition must be corrected as de-
scribed 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 re-
fractory hold-in, operate the burner until the refractory
reaches its maximum temperature. If the installation has a
multi-fuel burner, burn the heaviest fuel that is most likely
to reflect, bend or obscure the hot refractory steady infra-
red radiation. When the maximum refractory temperature
is reached, press the Stop Switch. If the FLAME LED
takes longer than three seconds after the flame goes out,
the infrared detector is sensing hot refractory. Do not open
the master switch.
NOTE: Some burners continue to purge their 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 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 an infrared detector, you can also try
lengthening the sight pipe or decreasing the pipe size
(diameter). For details, refer to the detector Instructions
and the equipment Operating Manual. Continue adjust-
ments until hot refractory hold-in is eliminated.
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