RM7890A,B,C/EC7890A,B 7800 SERIES RELAY MODULES
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PRINCIPAL TECHNICAL FEATURES
The RM/EC7890 provides all customary flame safeguard
functions as well as significant advancements in safety,
annunciation, and system diagnostics.
Safety Shutdown (Lockout) Occurs if:
1.
INITIATE PERIOD
a. AC line power errors occurred, see Operation.
b. Configuration jumpers have been changed (after
200 hours).
c. Four minute INITIATE period has been exceeded.
2.
STANDBY PERIOD
a. Flame signal is present after 240 seconds.
b. Ignition/intermittent pilot valve terminal is energized.
c. Internal system fault occurred.
d. Main valve terminal is energized.
e. Three second (two seconds for EC7890A1037,
RM7890A1064 and RM7890B1055) Flame Failure
Response Time (FFRT) Amplifier is installed and
configuration jumper is selected for relight (see
Table 3).
3.
SAFE START CHECK (EXCEPT RM7890C)
a. Ignition/intermittent pilot valve terminal is energized.
b. Internal system fault occurred.
c. Main valve terminal is energized.
4.
PILOT FLAME ESTABLISHING PERIOD (PFEP)
a. Ignition/intermittent pilot valve terminal is not
energized.
b. Internal system fault occurred.
c. Main valve terminal is energized.
d. No flame present at end of PFEP.
5.
RUN PERIOD
a. Ignition terminal is energized.
b. Internal system fault occurred.
c. Main valve terminal is not energized.
d. No flame present and configuration jumper is
selected for lockout.
e. Pilot valve terminal is not energized.
OPERATION
Sequence of Operation
The RM/EC7890 has the operating sequences listed below;
see Fig. 2. The RM/EC7890 LED provide positive visual
indication of the program sequence: POWER, PILOT, FLAME,
MAIN and ALARM.
Initiate
The RM/EC7890 enters the INITIATE sequence when the
relay module is powered. The RM/EC7890 can also enter 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 is initiated and is displayed on the
optional KDM 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
RM/EC7890 locks out. Causes for hold conditions in the
INITIATE sequence:
a. AC line dropout detection.
b. AC line noise that can prevent a sufficient reading of
the line voltage inputs.
c. Brownouts caused by a low line voltage.
NOTE: If a 3.0 second flame failure response amplifier is
installed and configuration jumper JR2 is intact, the
RM/EC7890 locks out. JR2 must be clipped.
Standby
The RM/EC7890 is ready to start an operating sequence
when the operating control input (terminal 6) recognizes a call
for heat. The burner switch, limits, operating limit control and
all microcomputer monitored circuits must be in the correct
state for the RM/EC7890 to continue into the Safe Start
Check.
Normal Start-Up Safe Start Check
(Except RM7890C)
The RM/EC7890 verifies that a flame or flame simulating
condition does not exist and proceeds into the Ignition Trial. If
a flame or flame simulating condition is present, the
RM/EC7890 remains in the STANDBY period. RM7890C
checks its internal components for flame simulating
conditions.
Ignition Trials
a. Pilot Flame Establishing Period (PFEP):
(1) The pilot valve and ignition transformer, termi-
nals 8 and 10, are energized. The RM/EC7890
has an intermittent pilot valve, terminal 8.
RM7890C closes internal relay contact in the “F”
lead.
(2) Flame must be proven by the end of the four- or
ten-second PFEP (30 seconds for
RM7890A1031) or a safety shutdown occurs.
(3) Once flame is proven, the ignition, terminal 10, is
de-energized and the main valve, terminal 9, is
energized.
(a)The RM7890B1030 finishes the 4- or 10-sec-
ond PFEP before the main valve is energized.
(b)The RM7890A1064, RM7890B1055/
EC7890A1037 with JR1 intact completes 10
second PFEP, shutting off ignition (Terminal
10) at 6 seconds. When the JR1 clipped these
devices complete a 4 second PFEP, shutting
off ignition (terminal 10) at 2 seconds.
Run
The RM/EC7890 is now in RUN and remains in RUN until the
controller input, terminal 6, opens, indicating that the demand
is satisfied or a limit has opened.
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