Honeywell 7800 Series Manual page 10

RM7888A
SAFETY PROVISIONS
EXPANDED SAFE-START CHECK
The conventional safe-start check, which prevents burner
start-up if flame is indicated at start-up, is expanded to
include a flame signal check during STANDBY, a safety
critical load check, a Limits Complete check, and an @Low
Fire check.
OFF CYCLE (STANDBY) FLAME
SIGNAL CHECK
The flame detection subsystem (flame detector and am-
plifier) is monitored during STANDBY. If a flame simulat-
ing condition or an actual flame exists for 40 seconds in
STANDBY, a safety shutdown occurs and startup is pre-
vented. If the flame signal exists at any time after 40 sec-
onds during STANDBY, a safety shutdown occurs and is
annunciated.
• A shutter-check amplifier and self-checking detector
are energized continuously during STANDBY and
the last two seconds of STANDBY. If a flame exists,
a safety shutdown will occur.
• An Amplicheck™ Amplifier is energized continu-
ally through STANDBY to detect any possibility of a
runaway detector or a flame. If either situation hap-
pens, a safety shutdown will occur.
• A standard amplifier is energized continually through
STANDBY to detect any possibility of a runaway det-
ector or a flame. If either situation happens, a safety
shutdown will occur.
TAMPER RESISTANT TIMING AND LOGIC
Safety and logic timings are inaccessible and cannot be
altered or defeated.
ALARM OPERATION
This output will supply power to the system master and/
or an external alarm indicator such as a bell or buzzer. The
alarm is turned on anytime a lockout has occurred and the
lockout condition has not been cleared. The alarm output is
also turned on when the reset button is pressed and held for
more than four seconds. The status of this output is not
monitored by the relay module.
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 RM7888A
hardware is running correctly.
Optional Multi-function Keyboard Display Module shows
elapsed time during PILOT IGNITION and MAIN IGNI-
TION. As an additional troubleshooting aid, it provides
65-0175
sequence timing, diagnostic information, historical infor-
mation and expanded annunciator information when a safety
shutdown or hold or normal operation occurs.
First-out Annunciation reports the cause of a safety shut-
down or identifies the cause of a failure to start or continue
the burner control sequence with an English text and num-
bered code via the Keyboard Display Module. It monitors
all field input circuits, including the flame signal amplifier
and output circuits. The system distinguishes modes of
failure and detects and annunciates difficult-to-find inter-
mittent failures.
Self-diagnostics add to the First-out Annunciation by
allowing the RM7888A to distinguish between field (exter-
nal device) and internal (system related) problems. Faults
associated within the flame detection subsystem or the
RM7888A are isolated and reported by the optional Key-
board Display Module. See Table 15, Hold and Fault
Message Summary, or the 7800 SERIES System Annun-
ciation Diagnostics and Troubleshooting, form 65-0118.
INTERLOCK REQUIREMENTS
The following interlock inputs are provided.
Limits Complete (Terminal 7)
This input provides an indication of the status of an
interlock string. If this input is energized, it is permissible to
operate through a burner sequence. The burner sequence
does not leave the Standby state if the Limits Complete
signal is de-energized. If this input becomes de-energized
after leaving the Standby state, one or more interlocks are
open and the burner sequence is either recycled or a lockout
occurs as defined for the particular burner state.
@Low Fire (Terminal 18)
This input will provide an indication of the low firing
rate position. If this input is energized, the motor position is
assumed by the relay module to be at the Low Fire position;
otherwise, the motor position cannot be determined if this
input is de-energized.
This signal is readable in any burner operating state
without regard to the status of the special function signals
or the Limits Complete signal. The RM7888 does not per-
form a test to assure that the Low Fire input signal becomes
energized when the High Fire motor control is commanded.
For example, the RM7888 will not detect a Low Fire input
that is jumpered or continuously energized without regard
to the actual motor position.
The High Fire position is not confirmed by a separate
high fire input at the RM7888. The system master control is
responsible for the High Fire proving and purging of the
combustion unit.
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