Honeywell 7800 Series Manual page 9

PREIGNITION OUTPUT CIRCUIT CHECK
At the end of PREPURGE, the Dynamic Safety Relay
operation is checked. Also, all safety critical loads termi-
nals 8, 9, 10 and 21, are checked to verify the terminals are
not powered. If the Dynamic Safety Relay operation is
faulty, or if any of the safety critical loads are powered,
safety shutdown occurs and is annunciated.
TAMPER RESISTANT TIMING AND LOGIC
Safety and logic timings are inaccessible and cannot be
altered or defeated.
VERIFIED SPARK TERMINATION
The ignition terminal is monitored to verify early spark
termination (five seconds ignition and pilot and five
seconds pilot only).
FIRST-OUT ANNUNCIATION AND
SELF-DIAGNOSTICS
Sequence Status Lights (LEDs) provide positive visual
indication of the program sequence: POWER, PILOT,
FLAME, MAIN and ALARM. The green POWER LED
blinks every four seconds, signifying that the RM7840
hardware is running correctly.
Optional multi-function Keyboard Display Module
shows elapsed time during PREPURGE, PILOT IGN,
MAIN IGN, and POSTPURGE. As an additional trouble-
shooting aid, it provides sequence timing, diagnostic
information, historical information and expanded annun-
ciator information when a safety shutdown or hold or
normal operation occurs.
First-out Annunciation reports the cause of a safety
shutdown or identifies the cause of a failure to start or
continue the burner control sequence with an English text
and numbered code via the optional Keyboard Display
Module. It monitors all field input circuits, including the
flame signal amplifier and firing rate position switches.
The system distinguishes 118 modes of failure and detects
and annunciates difficult-to-find intermittent failures.
Self-Diagnostics adds to the First-out Annunciation
by allowing the RM7840 to distinguish between field
(external device) and internal (system related) prob-
lems. Faults associated within the flame detection sub-
system, RM7840 or Plug-in Purge Card, are isolated
and reported by the optional Keyboard Display Mod-
ule, see the 7800 SERIES System Annunciation Diag-
nostics and Troubleshooting, form 65-0118.
INTERLOCK REQUIREMENTS
The following interlock inputs are provided:
Low Fire Interlock (RM7840 ALL)
This interlock verifies the firing rate motor is in the low
fire position before and during ignition trials.
High Fire Interlock (RM7840E,L)
This interlock verifies the firing rate motor is in the
high fire position before and during PREPURGE. If the
High Fire Switch is jumpered on the RM7840E, the
Energy Saving function will not be performed.
Running Interlock (RM7840G,M)
This interlock (ILK) input signifies a Running Inter-
lock. If a Running Interlock is open at the beginning of
PREPURGE, a 30 second hold condition is initiated. If 30
seconds elapse and the Running Interlock still has not
closed, a lockout will occur. After entering PREPURGE,
if the Running Interlock opens during the first ten seconds,
the purge timer will be reset. This provides a continuous
PURGE to occur without interruption before the Pilot
Flame Establishing Period. If the Running Interlock opens
after ten seconds into PREPURGE, it will recycle back to
the beginning of PREPURGE. If it opens anytime during
the Ignition Trials or Run, it will proceed to POSTPURGE.
A typical Running Interlock string contains an Airflow
Switch (see Fig. 9 and 11). The Interlock Check is a site
configurable option (see Table 6). If this feature is en-
abled, the RM7840 will lockout after 120 seconds when-
ever control terminal 6 is energized, and the Running
Interlock string (including Airflow Switch) is closed dur-
ing STANDBY.
Lockout Interlock (RM7840E,L)
This interlock (ILK) input signifies a Lockout Inter-
lock. If the Lockout Interlock is open for more than ten
seconds into PREPURGE, the RM7800E,L will lockout.
After entering PREPURGE, if the Lockout Interlock opens
during the first ten seconds, the purge timer will be reset.
This provides a continuous PURGE to occur without
interruption before the Pilot Flame Establishing Period. If
a Lockout Interlock opens anytime after ten seconds into
PURGE, during the Ignition Trials or Run, it causes a
lockout.
A typical Lockout Interlock string contains an Airflow
Switch (see Figs. 8 and 10). The Interlock Check is a site
configurable option (see Table 6). If this feature is en-
abled, the RM7840 will lockout after 120 seconds when-
ever control terminal 6 is energized, and the Lockout
Interlock string (including Airflow Switch) is closed dur-
ing STANDBY.
NOTE: For the RM7840E, the ten second time frame does
not begin until the blower motor is recognized.
Preignition Interlock (RM7840 ALL)
The Preignition Interlock input is typically connected
to a proof-of-closure switch for a fuel valve(s). The
Preignition Interlock must be energized throughout
PREPURGE. If the Preignition Interlock opens during
STANDBY, it causes a hold (30 seconds). The RM7840
will lockout if the interlock does not close within 30
seconds during STANDBY. If the Preignition Interlock
opens during PREPURGE, it will recycle to STANDBY
(RM7840G,M) or will lockout (RM7840E,L). If the Pre-
ignition Interlock is open after five seconds into
POSTPURGE, the RM7840 will lockout. The Preignition
Interlock is ignored during the ignition trials state and
during RUN.
9
RM7840E,G,L,M
SAFETY PROVISIONS
65-0087—2