Honeywell 7800 Series Manual page 29

IMPORTANT: You have eight seconds or three seconds,
depending on PFEP selected, to position the Run/Test
Switch in the TEST position to stop the sequence after
the start of the PILOT IGN period.
7. Turn the pilot pressure down very slowly, reading the
manometer (or pressure gauge) as it drops. Stop instantly
when the FLAME LED goes out. Note the pressure at the
RM7840 flame relay dropout point. The pilot is at the
minimum turndown position. Immediately turn up the pilot
pressure until the FLAME LED comes on again.
NOTE: If there is no flame for fifteen seconds with the
sequence stopped at this point, the RM7840 will lockout.
8. Repeat step 7 to verify the pilot gas pressure reading at
the exact point the FLAME LED light goes out.
9. 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 or until
the flame signal increases to 1.25 Vdc.
10. 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 18.
NOTE: This step requires two people, one to open the manual
valve(s) and one to watch for ignition.
11. 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.
12. Recycle the burner and stop the sequence in the
PILOT IGN period by using the Run/Test Switch.
13. Increase the pilot flame size by increasing its fuel
flow until a smooth main flame is accomplished.
14. Reposition the flame scanner sight tube or use
orifices until the pilot flame signal voltage is in the range
of 1.25 - 1.50 Vdc.
15. 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.
16. If used, remove the bypass jumpers from the sub-
base terminals, limits/controls or switches.
17. Run the system through another cycle to check for
normal operation.
18. 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 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. 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 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 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 refrac-
tory 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 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 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 refrac-
29
RM7840E,G,L,M
CHECKOUT
65-0087—2