7800 SERIES EC7890A,B/RM7890A,B RELAY MODULE
65-0204–1
17
OPERATION
Sequence of Operation
The 7890 has the following operating sequences, see Fig. 14
and 16.
Initiate
The 7890 enters the INITIATE sequence if the Relay Module
verifies voltage fluctuations of +10/-15% or frequency
fluctuations of +/- 10% 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 will be initiated
and will be displayed on the optional VFD for at least five
seconds. When the tolerances are met, the INITIATE
sequence will restart. If the condition is not corrected and the
hold condition exists for four minutes, the 7890 will lockout.
Causes for hold conditions in the INITIATE sequence are:
•
AC line dropout detected.
•
AC line frequency error caused by using a 60 Hz device
on a 50 Hz line or vice versa.
•
AC line noise can prevent a sufficient reading of line
voltage inputs.
•
Brownouts caused by low line voltage.
Standby
The 7890 is ready to start an operating sequence when the
operating control input determines a
call for heat is present.
The burner switch, limits, operating limit control and all
microcomputer monitored circuits must be in the correct state
for the 7890 to continue into the Safe-Start Check.
Normal Start-Up Safe-Start Check
The 7890 verifies that a flame does not exist and proceeds
into the Ignition Trial. If a flame is present, the 7890 will
recycle to the STANDBY period. If the critical loads are not in
the correct state, a safety shutdown occurs.
Ignition Trials
1
Pilot Flame Establishing Period (PFEP):
a.
The pilot valve and ignition transformer, terminals
8 and 10, are energized. The 7890A,B has an
intermittent pilot valve, terminal 8.
b.
Flame must be proven by the end of the 4 or 10
second PFEP to allow the sequence to continue.
If flame is not proven by the end of PFEP, a
safety shutdown occurs.
c.
With flame proven, the ignition, terminal 10, is
de-energized and the main valve, terminal 9, is
energized.
Run
The 7890 is now in RUN and will remain in RUN until the
controller input, terminal 6, opens, indicating that the demand
is satisfied or a limit has opened.
Selectable Site-Configurable Jumpers
The 7890 has two site-configurable jumper options, see
Fig. 17 and Table 3. The site-configurable jumpers should be
clipped with side cutters and the resistors removed from the
Relay Module.
Fig. 14. 7890A,B sequence.
POWER
00
LED
DISPLAY
OPERATING
CONTROLLER
AND LIMITS
BURNER
START
FLAME
SIGNAL
INITIATE
ALARM
POWER
STANDBY
POWER
POWER
PILOT
FLAME
MAIN
PFEP
4 OR 10 SEC
PILOT
FLAME
MAIN
POWER
RUN
STANDBY
4/10
IGNITION
INTERMITTENT PILOT
MAIN VALVE
LIMITS AND BURNER CONTROL CLOSED
9
8
10
3
6
TO
M11191
00
POWER
SAFE-
START
MAIN FUEL VALVE WILL BE ENERGIZED DURING PFEP IF FLAME IS PROVEN.
1
1
ALARM
S S C
SAFE START CHECK
FLAME PROVING
