11 65-0120—1
RM7838B
SAFETY PROVISIONS
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 RM7838B if the detection system
fails.
DYNAMIC INPUT CHECK
All system input circuits are examined to ensure the
RM7838B is capable of recognizing the true status of
external controls, limits and interlocks. If any input fails
this test, a safety shutdown will occur and the fault will be
annunciated.
DYNAMIC SAFETY RELAY TEST
Checks the ability of the dynamic safety relay contacts to
open and close. It also verifies that the safety critical loads,
terminals 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 while
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 will occur 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, a preigni-
tion interlock check, an airflow switch check, and a safety
critical load check.
HIGH PURGE RATE AND LOW FIRE START
SWITCH TESTS
High Purge Rate Switch Test examines the Purge Position
Interlock Switch at the moment the firing rate motor is
commanded to the High Purge Rate position. If the switch is
bypassed, welded or otherwise closed prematurely, the sys-
tem will automatically add 30 second hold to allow addi-
tional drive time for the firing rate motor to reach or near the
open position before starting the purge timing; otherwise,
purge timing starts when the High Purge Rate Switch is
closed. Four minutes, 15 seconds is allowed for the closure
of the High Purge Rate Switch or a hold of four minutes,
15 seconds is initiated if the switch opens during purge. The
RM7838B will lockout and annunciate an alarm if the
switch fails to close within the hold time period.
Low Fire Start Switch Test examines the Low Fire Start
Switch at the moment PURGE is completed. If the switch is
bypassed, welded or otherwise prematurely closed, the sys-
tem automatically adds a 30 second hold to allow the firing
rate motor additional time to reach or be near the low fire start
position before ignition trials; otherwise, ignition trials start
after the Low Fire Switch closes. The test also is used to
prove that the firing rate motor is at low fire position through-
out the ignition trial period. This switch will also cause a hold
(four minutes 15 seconds) condition if the switch opens after
purging is complete. The RM7838B will lockout and an-
nunciate an alarm if the switch fails to close within the hold
time period.
OFF CYCLE (STANDBY OR PURGE) FLAME
SIGNAL CHECK
The flame detection subsystem (flame detector and amp-
lifier) monitors the shutter-check amplifier and self-check-
ing detector for the first 40 seconds during STANDBY and
the last two seconds of STANDBY before entering the
PURGE period. If a flame exists, a safety shutdown will
occur.
PREIGNITION OUTPUT CIRCUIT CHECK
At the end of PURGE, the Dynamic Safety Relay opera-
tion is checked. Also, all safety critical loads, terminals 8, 9
and 10, 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). If four seconds PFEP is selected, there is no Early
Spark Termination.
PILOT VALVE HOLD (TERMINAL NO. 16)
If closed on startup, the RM7838B will hold in pilot.
When initiated with an input to the RM7838B (terminal
no. 16) from the RUN condition, The RM7838B commands
the firing rate motor to the low fire position. The pilot valve
(terminal 8) is commanded on for 45 seconds while the
main valve (terminal no. 9) is held on. The main valve
(terminal 9) is then turned off and ignition (terminal 10) is
turned on for 10 seconds. Failure to light the pilot or
proving of the low fire switch will result in a safety shut--
down with the fault annunciated.
Safety shutdown will occur if Non Shutter Check Ampli-
fier/Detector is uded.
MANUAL OPEN VALVE (TERMINAL NO. 17)
The RM7838B will hold in PFEP indefinitely until the
Manual Open Valve Input (terminal 17) is powered. A ten
second MFEP is now initiated to light the main flame.
With Configuration Jumper JR3 clipped, the ten second
MFEP is started. Manual Open Valve Input (terminal 17)
must be closed in ten seconds or safety shutdown occurs.
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 to signify the RM7838B hardware
is running correctly.
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