Honeywell 7800 Series Product Data page 8

7800 SERIES RM7896A,B,C,D RELAY MODULE
5. Main Flame Establishing Period (MFEP) (RM7896C,D)
a. Airflow lockout feature is enabled and the airflow
switch opens.
b. Ignition terminal is energized.
c. Ignition/pilot valve terminal is not energized.
d. Main valve terminal is not energized.
e. Delayed main valve terminal is energized.
f. No flame present at end of MFEP.
g. Internal system fault occurred.
h. Purge card is removed.
i. Purge card is bad.
6. RUN Period
a. No flame present.
b. Airflow lockout feature is enabled and the airflow
switch opens.
c. Interrupted pilot valve terminal is energized
(RM7896C,D).
d. Main valve terminal is not energized.
e. Delayed main valve terminal is not energized
(RM7896C,D).
f. Internal system fault occurred.
g. Purge card is removed.
h. Purge card is bad.
7. POST PURGE Period
a. Ignition terminal is energized.
b. Ignition/pilot valve terminal is energized.
c. Main valve terminal is energized.
d. Delayed main valve terminal is energized
(RM7896C,D).
e. Internal system fault occurred.
f. Purge card is removed.
g. Purge card is bad.
SAFETY PROVISIONS
Internal Hardware Status Monitoring
The RM7896 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 RM7896 will lockout on safety shutdown.
The RM7896 must react to input changes but avoid the
occurrence of nuisance shutdown events. Signal conditioning
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
RM7896 if the flame amplifier fails.
65-0193
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 RM7896 if the detection system fails.
Dynamic Input Check
All system input circuits are examined to assure that the
RM7896 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, terminals 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.
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 amplifier)
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 seconds during
STANDBY and the last two seconds before exiting STANDBY.
If a flame exists, a safety shutdown occurs. An Ampli-Check
Amplifier is energized continually 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).
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