Honeywell 7800 Series Manual page 41

9. Energize the appropriate special function input (ter-
minal 17, 19, or 20) and let the sequence proceed. At ten
seconds into the Ignition Trial period, make sure the auto-
matic main fuel valve(s) open; then smoothly open the
manual main fuel shutoff valve(s) (or any other manually
opened safety shutoff valve(s), if used) and watch for main
burner ignition. If the main burner flame is established,
proceed to step 14.
NOTE: This step requires two people, one to open the manual
valve(s) and one to watch for ignition.
10. If the main burner flame is not established within five
seconds, or within the normal lightoff time specified by the
equipment manufacturer, close the manual main fuel shutoff
valve(s) and open the master switch. If the lightoff was
rough, the pilot flame size is too small.
11. Recycle the burner and stop the sequence in PILOT
IGN period.
12. Increase the pilot flame size by increasing its fuel
flow until a smooth main flame is accomplished.
13. Reposition the flame scanner sight tube or use ori-
fices until the pilot flame signal voltage is in the range of
1.25 to 1.50 Vdc.
14. 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 the recommendation of the
equipment manufacturer.
15. If used, remove the bypass jumpers from the subbase
terminals, limits/controls or switches.
16. Run the system through another cycle to check for
normal operation.
17. Return the system to normal operation.
IGNITION INTERFERENCE TEST
(ALL FLAME RODS)
Test to make certain 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, it will cause a safety shutdown. If it in-
creases the flame signal, it could cause the FLAME LED to
come on when the true flame signal is below the minimum
acceptable value.
Start the burner and measure the flame signal with both
ignition and pilot (or main burner) on, and then with only
the pilot (or main burner) on. Any significant difference
(greater than .5 Vdc) indicates ignition interference.
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. 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 refrac-
tory heats up indicates hot refractory saturation. If satura-
tion 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 REFRACTORY 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 condi-
tion 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 maxi-
mum temperature. Then terminate the firing cycle by low-
ering 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 flick-
ering 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 refrac-
tory 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
41
RM7888A
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