Honeywell 7800 Series Product Data page 25

NOTE: If there is no flame for fifteen seconds with the
sequence stopped at this point, the RM7896
will lockout.
9. Repeat step 8 to verify the pilot gas pressure reading at
the exact point the FLAME LED light goes out.
10. Increase the pilot pressure immediately until the
FLAME LED comes on, and then turn it down slowly to
obtain a pressure reading just above the dropout point.
NOTE: Step 11 requires two people—one to open the
manual valve(s) and one to watch for ignition.
11. Set the Run/Test Switch in the RUN position and let the
sequence proceed. At ten seconds into the Ignition Trial
period, make sure the automatic 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 16.
12. 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.
13. Recycle the burner and stop the sequence in the PILOT
IGN period by using the Run/Test Switch.
14. Increase the pilot flame size by increasing its fuel flow
until a smooth main flame is accomplished.
15. Reposition the flame scanner sight tube or use orifices
until the pilot flame signal voltage is approximately 1.25 -
1.50 Vdc.
16. When the main burner lights reliably with the pilot at
turndown, disconnect the manometer (or pressure
gauge) and turn up the pilot gas flow to that
recommended by the equipment manufacturer.
17. If used, remove the bypass jumpers from the subbase
terminals, limits/controls or switches.
18. Run the system through another cycle to check for
normal operation.
19. 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, it will cause a safety shutdown. 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.
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. Be sure there is enough ground area.
2. Be sure the ignition electrode and the flame rod are on
opposite sides of the ground area.
7800 SERIES RM7896A,B,C,D RELAY MODULE
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
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 adjustments 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 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 heaviest fuel that is most likely to reflect,
bend or obscure the hot refractory steady infrared radiation.
When the maximum refractory temperature is reached,
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