Safety Provisions - Honeywell 7800 Series Manual

INTERNAL HARDWARE STATUS MONITORING
The RM7895 checks the purge card for correct parity to
prevent purge timing shifts and circuitry failures. It also
analyzes the integrity of the configuration jumpers and
internal hardware. The POWER LED will blink every four
seconds, signifying an internal hardware check.
CLOSED LOOP LOGIC TEST
The test verifies the integrity of all safety critical loads,
terminals 8, 9, 10 and 21. If the loads are not energized
properly; i.e., the main valve terminal is powered during
PREPURGE, the RM7895 will lockout on safety shut-
down. The RM7895 must react to input changes but avoid
the occurrence of nuisance shutdown events. Signal condi-
tioning is applied to line voltage inputs to verify proper
operation in the presence of normal electrical line noise
such as transient high voltage spikes or short periods of line
dropout. Signal conditioning is tolerant of synchronous
noise (line noise events that occur at the same time during
each line cycle).
DYNAMIC AMPLI-CHECK™
Dynamic AMPLI-CHECK™ circuitry tests the flame
signal amplifier during burner operation and shuts down the
RM7895 if the flame amplifier fails.
DYNAMIC FLAME AMPLIFIER AND SHUTTER
CHECK
Self-checking circuitry tests all electronic components
in the flame detection system and amplifier 10 to 12 times
per minute and shuts down the RM7895 if the detection
system fails.
DYNAMIC INPUT CHECK
All system input circuits are examined to assure that the
RM7895 is capable of recognizing the true status of external
controls, limits and interlocks. If any input fails this test, a
safety shutdown occurs and the fault will be annunciated.
DYNAMIC SAFETY RELAY TEST
Checks the ability of the dynamic safety relay contact to
open and close. Verifies that the safety critical loads, termi-
nals 8, 9, 10 and 21, can be de-energized, as required, by the
Dynamic Self-Check logic.
DYNAMIC SELF-CHECK SAFETY CIRCUIT
The microcomputer tests itself and related hardware, and
at the same time, the safety relay system tests the microcom-
puter operation. If a microcomputer or safety relay failure
occurs and does not allow proper execution of the self-check
routine, safety shutdown occurs and all safety critical loads
will be de-energized.

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, an airflow switch
check and a safety critical load check.
OFF CYCLE (Standby or Prepurge) FLAME
SIGNAL CHECK
The flame detection subsystem (flame detector and ampli-
fier) is monitored during STANDBY. If a flame simulating
condition or an actual flame exists, a system hold occurs and
start-up is prevented. If the flame signal exists at any time
after the first 40 seconds of STANDBY, a safety shutdown
occurs and is annunciated. A shutter-check amplifier and
self-checking detector are energized for the first 40 sec-
onds during STANDBY and the last two seconds before
exiting STANDBY. If a flame exists, a safety shutdown
occurs. An AMPLI-CHECK™ Amplifier is energized con-
tinually through STANDBY and PREPURGE to detect any
possibility of a runaway detector or a flame. If a flame
exists, a safety shutdown occurs. A standard amplifier is
energized continually through STANDBY and PREPURGE;
if a flame exists, a safety shutdown occurs.
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 assure early spark
termination (ten seconds ignition and pilot and ten seconds
pilot and main 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 RM7895
hardware is running correctly.
Optional multi-function Keyboard Display Module
shows elapsed time during PREPURGE, PILOT IGN and
MAIN IGN. As an additional troubleshooting aid, it pro-
vides sequence timing, diagnostic information, historical
information and expanded annunciator 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. The system distinguishes 43 modes
of failure and detects and annunciates difficult-to-find inter-
mittent failures.
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RM7895A,B,C,D
SAFETY PROVISIONS
65-0086—2