Honeywell 7800 SERIES Manual page 23
7800 series rm7890a,b,c relay module
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NOTE: If there is not flame present for the selected Flame
Failure Response Test (FFRT), the RM7890 will lock-
out.
a. If the Flame Failure Action jumper (see Table 3,
JR2) is not clipped: allow the RM7890A,B to
recycle to PILOT IGNITION. If the Flame Failure
Action jumper is clipped: push the reset pushbutton
and allow the RM7890A,B to recycle to PILOT
IGNITION.
b. As the control attempts to relight the pilot, 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 approxi-
mately 1.25 Vdc. This step must be completed
within four or ten seconds, depending on the se-
lected PFEP, or lockout will occur.
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 that 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.
Then return to step 6a. If the burner flame is
established in the normal lightoff period, proceed to
step 10.
7. Recycle the burner and let the sequence advance to the
PILOT IGN period.
8. Increase the pilot flame size by increasing its fuel flow
until a smooth main flame is accomplished.
9. Reposition the flame scanner sight tube or use orifices
until the pilot flame signal voltage is approximately 1.25 -
1.50 Vdc.
10. 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.
11. If used, remove the bypass jumpers from the subbase
terminals, limits/control or switches.
12. Run the system through another cycle to check for
normal operation.
13. 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.
RM7890A,B,C
CHECKOUT
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. 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 detec-
tion 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 refrac-
tory 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 refrac-
tory 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 goes out. If the
FLAME LED is on 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
Page 23
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