CB780E/CB784E RELAY MODULES WITH VALVE PROVING
750-234
27
32-00150—03
OPERATION
Sequence of Operation
The CB780E/CB784E has the following operating
sequences, see Fig. 8–10. The CB780E/CB784E LED
provide positive visual indication of the program
sequence: POWER, PILOT, FLAME, MAIN and ALARM.
Initiate
The CB780E/CB784E enters the INITIATE sequence when
the Relay Module is powered. The CB780E/CB784E can
also enter the INITIATE sequence if the Relay Module
verifies voltage fluctuations of +10/-15 percent or
frequency fluctuations of +/-10 percent during any part of
the operating sequence. The INITIATE sequence lasts for
ten seconds unless the voltage or frequency tolerances
are not met. When the tolerances are not met, a hold
condition is initiated and displayed on the VFD for at least
five seconds. When the tolerances are met, the INITIATE
sequence restarts. If the condition is not corrected and the
hold condition exists for four minutes, the
CB780E/CB784E locks out. Causes for hold conditions in
the INITIATE sequence:
a. AC line dropout is detected.
b. AC line noise prevents a sufficient reading of the
line voltage inputs.
c. Low line voltage brownouts occur.
The INITIATE sequence also delays the burner motor
starter from being energized and de-energized from an
intermittent AC line input or control input.
Standby
The CB780E/CB784E is ready to start an operating
sequence when the operating control determines a call for
heat is present. (Terminal 6, or Terminal 17 if Valve Proving
is required.) The burner switch, limits, operating control
and all microcomputer monitored circuits must be in the
correct state for the CB780E/CB784E to continue into the
PREPURGE sequence.
Pre-Purge
Purge timers provide Pre-Purge timings selectable from
30 seconds to 2 1/2 minutes:
a. The operating control (terminal 6, or terminal 17
for valve proving), Running Interlocks, Pre-Igni-
tion Interlocks, Burner Switch, Run/Test Switch,
Lockout Interlocks and all microcomputer moni-
tored circuits must be in the correct operating
state.
b. The blower motor output, terminal 5, is powered
to start the PREPURGE sequence. The firing rate
motor is driven to the high fire position. The PRE-
PURGE timing does not begin until the Lockout
Interlock String and High Fire Switch are both
closed.
c. If Before, Split or Both Valve Proving tests are
selected (and demand input T17 is used), the
CB780E/CB784E will sequence the main valves
to conduct the VP tests concurrently with Pre-
Purge (beginning at 10 seconds into the purge
time).
d. The Pre-Ignition Interlock input must remain
closed throughout PREPURGE (except during VP
testing); otherwise, safety shutdown occurs for
the CB780E/CB784E.
e. The Lockout Interlock inputs (interlock circuit
including Airflow Switch) must close by ten sec-
onds after demand; otherwise, a safety shutdown
for the CB780E/CB784E occurs.
f.
When PREPURGE timing is complete, the firing
rate motor drives to the low fire position.
g. When the firing rate motor reaches low fire posi-
tion, the Low Fire Switch, terminal 18, input must
be energized before entering the Ignition Trial
state.
Ignition Trials—Pilot Lighted System
(Except VP System with DSI)
1.
Pilot Flame Establishing Period (PFEP):
To get pilot lighted system on VP system, Jumper 2
must be removed. Default is direct spark ignition.
a. With the firing rate motor at the low fire position:
(1) With the demand on terminal 6, the pilot valve
and ignition transformer, terminals 8, 10 and
21, are energized. With the demand on termi-
nal 17 (operating as Valve Proving), the
CB780E/CB784E has a 15-second inter-
rupted pilot valve, terminal 21. The
CB780E/CB784E have a ten-second inter-
rupted pilot valve/ignition, terminal 8. Termi-
nal 21 is Main Valve 2 only.
(2) During PFEP, the Low Fire Switch must
remain closed. If it opens, a safety shutdown
occurs.
(3) The Pre-Ignition Interlock input is ignored
throughout the Ignition Trial state.
b. Flame must be proven by the end of the ten-sec-
ond PFEP (four if JR1 is clipped) to allow the
sequence to continue. If flame is not proven by
the end of PFEP, a safety shutdown occurs.
c. After five seconds, the ignition, terminal 10, is
de-energized for early spark termination.
2.
Main Flame Establishing Period (MFEP):
a. Terminal 9 (and 21 in VP mode) is energized
when the presence of flame is verified at the end
of a 10-second Pilot Flame Establishing Period
(PFEP) (four seconds if JR1 is clipped).
b. Terminal 8 is turned off 10 seconds after Termi-
nal 9 (and Terminal 21) is energized.
c. Terminal 21 action demand on Terminal 6 (with-
out Valve Proving Function) is de-energized 15
seconds after Terminal 9 is energized.
Ignition Trials—Valve Proving with DSI
System
1.
Demand connected to Terminal 17:
—
JR2 Intact on the CB780E/CB784E
a. Ignition, Main Valve 1 and Main Valve 2, Termi-
nals 10, 9, and 21 turn on together.
b. Flame must be proven at the end of the 4 second
Main Flame Establishing Time.
c. Ignition, Terminal 10 is turned off. System now in
Run.
d. If Flame is not proven, safety lockout occurs.
