Principle Technical Features; Safety Provisions - Honeywell 7800 SERIES Manual

RM7890A,B,C
PRINCIPAL TECHNICAL FEATURES • SAFETY PROVISIONS
The RM7890 provides all customary flame safeguard
functions while providing significant advancements in the
areas of 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 40 seconds.
b. Ignition/intermittent pilot valve terminal is ener
gized.
c. Internal system fault occurred.
d. Main valve terminal is energized.
e. Three second Flame Failure Response Time
(FFRT) Amplifier is installed and configuration
jumper is selected for relight (see Table 3).
INTERNAL HARDWARE STATUS MONITORING
The RM7890 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 and 10. If the loads are not energized properly;
i.e., the main valve terminal is powered during STANDBY,
the RM7890 will lockout on safety shutdown. The RM7890
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
RM7890 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 12 times per minute
and shuts down the RM7890 if the detection system fails.
DYNAMIC INPUT CHECK
All system input circuits are examined to assure that the
RM7890 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.
65-0126—2
Principal Technical Features
3. SAFE START CHECK (EXCEPT RM7890C)
a. Ignition/intermittent pilot valve terminal is ener-
gized.
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 en-
ergized.
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 se-
lected for lockout.
e. Pilot valve terminal is not energized.
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 and 10, 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
(EXCEPT RM7890C)
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 and a safety critical
load check.
OFF CYCLE (STANDBY) FLAME SIGNAL CHECK
(EXCEPT RM7890C)
The flame detection subsystem (flame detector and ampli-
fier) is monitored during STANDBY. If a flame simulating
condition or an actual flame exists for 40 seconds in
STANDBY, a system hold occurs and start-up is prevented.
If the flame signal exists at any time after the 40 seconds
during STANDBY, a safety shutdown occurs and is annun-
ciated. 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 after the first 40 seconds of STANDBY, the shutter-
check amplifier and self-checking detector are energized
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Safety Provisions