7800 SERIES EC7885A/RM7885A RELAY MODULE
65-0203
25
9. If the main flame is not established within five seconds or
the normal lightoff period specified by the burner manu-
facturer, close the manual main fuel shutoff valve(s) and
open the master switch. If the burner flame is established
in the normal lightoff period, proceed to step 11.
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
approximately 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 up the pilot gas flow 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 (in-
crease) the flame signal. If it decreases the flame signal enough,
the 7885A does 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 interference is
or was 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 (Rectifying
Photocell or All Infrared Detectors)
Test to be sure hot refractory is not delaying 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 (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 stopped glowing. 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, 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) allows
purging of the combustion chamber. This reduces
fuel vapor buildup 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 adjustments until hot refractory hold-in is
eliminated.
