Honeywell 7800 SERIES EC7895A Product Data page 24

7800 SERIES EC7895A, RM7895A RELAY MODULE
c. Turn the pilot back down slightly but not enough
to cause the FLAME LED to go out. (Keep the
pilot gas pressure just above the reading noted in
step 6 above.)
NOTE: Step d requires two people, one to open the manual
main fuel valve(s) and one to watch for ignition.
d. With the sequence in the normal burner run
mode, make sure the automatic main fuel
valve(s) is open. Smoothly open the manual main
fuel shutoff valve(s) and watch for main burner
lightoff.
e. If the main flame is not established within five
seconds or the normal lightoff period specified by
the burner manufacturer, close the manual main
fuel shutoff valve(s) and open the master switch.
Return to step 6. If the burner flame is
established in the normal lightoff period, proceed
to step 16.
7. 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.
8. If used, remove the bypass jumpers from the subbase
terminals, limits/controls or switches.
9. Run the system through another cycle to check for
normal operation.
10. 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 causes 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 accep-table 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.
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.
65-0205
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 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 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
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, 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 Fuel Selector 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) 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.
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