7800 SERIES EC7890A,B/RM7890A,B RELAY MODULE
65-0204–1
24
6
After the sequence has entered the normal burner run
period, turn down the pilot gas pressure very slowly,
reading the manometer (or gauge) as the pressure
drops. Stop immediately when the FLAME LED goes
out. Note the pressure at this point.
NOTE:
If there is no flame present for the selected
Flame Failure Response Test (FFRT), the
7890 will lock out.
a.
If the Flame Failure Action jumper (see Table 3,
JR2)
is not clipped, allow the 7890A,B to recycle
to PILOT IGNITION. If the Flame Failure Action
jumper
is clipped, push the reset pushbutton and
allow the 7890A,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 approximately 1.25 Vdc. This step must be
completed within four or ten seconds, depending
on the selected 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
to 1.50 Vdc.
J
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.
K
If used, remove the bypass jumpers from the subbase
terminals, limits/control or switches.
L
Run the system through another cycle to check for
normal operation.
M
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
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; 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
