7800 SERIES EC7885A/RM7885A RELAY MODULE
65-0203
19
OPERATION
Sequence of Operation
The operating sequence for the 7885A follows, see Figs. 17,
18, and Table 3.
NOTE:
The alarm will sound until a flame is sensed.
Initiate
The 7885A enters the INITIATE sequence when the Relay
Module is powered. The 7885A can also enter the INITIATE
sequence when the Relay Module verifies voltage fluctuations
of +10/-15% or frequency fluctuations of +/-10% during start-
up or run sequences. 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 is displayed on the optional 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 7885A locks out.
Causes for hold conditions in the INITIATE sequence are:
•
AC line dropout is detected.
•
Brownouts caused by a low line voltage.
•
AC line noise that can prevent a sufficient reading of the
line voltage inputs.
Standby
The 7885A will be in the STANDBY mode after it has
completed the INITIATE startup or the Stop Switch has been
pressed. The POWER LED will blink every four seconds,
signifying an internal hardware check has been completed.
The ALARM LED will also be lit and an external alarm will be
activated.
Normal Start-Up
When the Start Switch is pressed, the Ignition Transformer is
energized and power is applied to terminal 10 of the 7885A. If
all microcomputer monitored circuits are in the correct state,
the 7885 will initiate a Safe-Start Check and Ignition Trials.
Safe Start Check (Two Seconds)
The 7885A conducts a two-second Safe-Start Check as it
verifies that critical loads are in the proper state prior to start-
up and that no flame is present in the combustion chamber.
Ignition Trials
After completing a successful Safe-Start Check, the 7885 will
provide power to the Intermittent Pilot Valve, terminal 8 and
turn on the PILOT LED.
When flame is proven, the FLAME LED lights, the ALARM
LED shuts off and the RM7885 brings on the Main Valve and
turn on the MAIN LED.
The Start Switch can now be released, which shuts off the
Ignition Transformer.
NOTE:
THE PILOT VALVE Follows the Start Switch until the
flame is proven. Then it is in control of the 7885 (for
example, pushing and releasing the Start Switch
brings on and shuts off the Ignition Transformer and
the Pilot Valve until the flame is proven.)
Run
The 7885A is now in RUN and remains in RUN until the Stop
Switch is pressed or a Limit opens terminal 6.
INITIATE
POWER
PILOT
FLAME
MAIN
ALARM
ALARM
ALARM
STANDBY
POWER
POWER
PILOT
FLAME
MAIN
RUN
STANDBY
BURNER
START
START SWITCH
MAIN VALVE
LIMITS, STOP STATION AND ALARM SLICENING SWITCH CLOSED
INTERMITTENT PILOT
SAFE START CHECK
FLAME PROVING
LED
DISPLAY
POWER
PILOT
FLAME
MAIN
PFEP
POWER
SAFE-
START
POWER
POWER
LIMITS, STOP
STATION AND
SILENCING SWITCH
FLAME
SIGNAL
1
1
7885
MAIN FUEL VALVE IS ENERGIZED DURING PFEP IF FLAME IS PROVEN.
M11183
00
00
15 MINUTES
L1 TO
6
9
8
10
Fig. 17. 7885 sequence.
