CB780E/CB784E RELAY MODULES WITH VALVE PROVING
750-234
7
32-00150—03
c. High Fire Switch fails to close within four min-
utes, and fifteen seconds after firing rate motor
is commanded to drive to high fire position at
start of PREPURGE.
d. Low Fire Switch fails to close within four minutes,
and fifteen seconds after firing rate motor is
commanded to drive to low fire position at end of
PREPURGE.
e. Lockout Interlock does not close within 10 sec-
onds.
f.
Lockout Interlock opens during PREPURGE.
g. Ignition/pilot valve terminal is energized.
h. Main valve terminal is energized (except during
Value Proving testing).
i.
Internal system fault.
5.
PILOT FLAME ESTABLISHING Period (PFEP)
a. Low Fire Switch opens.
b. Lockout Interlock opens.
c. Ignition/pilot valve terminal is not energized.
d. Early Spark Termination terminal is energized
after five seconds.
e. No flame is present at end of PFEP.
6.
MAIN FLAME ESTABLISHING Period (MFEP)
a. Low Fire Switch opens.
b. Lockout Interlock opens.
c. Ignition/pilot valve terminal is not energized.
d. Main valve terminal is not energized.
e. No flame is present at end of MFEP.
7.
RUN Period
a. No flame is present.
b. Lockout Interlock opens.
c. Interrupted pilot valve terminal is energized.
d. Main valve terminal is not energized.
8.
POSTPURGE Period
a. Pre-Ignition Interlock does not close in five sec-
onds and opens after five-second time period
(except
during Value Proving testing).
b. Ignition/pilot valve terminal is energized.
c. Main valve terminal is energized (except during
Valve Proving testing)
SAFETY PROVISIONS
Internal Hardware Status
Monitoring
The CB780E/CB784E 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 blinks 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 CB780E/CB784E will lockout on safety
shutdown. The CB780E/CB784E 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
CB780E/CB784E 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 CB780E/CB784E if the
detection system fails.
Dynamic Input Check
All system input circuits are examined to verify that the
CB780E/CB784E 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 is
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, 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 while
at the same time the safety relay system tests the
microcomputer 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
preignition interlock check, an interlock check, and a
safety critical load check.
High Fire Purge and Low Fire Start
Switch Tests
High Fire Purge Switch Test
examines the Purge Position
Interlock Switch at the moment the firing rate motor is
commanded to the high fire position. If the switch is
bypassed, welded or otherwise closed prematurely, the
system will automatically add 30 seconds to allow
additional 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 Fire Switch
is closed. This switch will also cause a hold (four minutes,
fifteen seconds) condition when the switch is open before
