Product Overview

RM7890; RM7895 100 VAC 7800 SERIES RELAY MODULES
66-1195—01 6
Table 5. Sequence Timing for Normal Operation.
a
Standby and Run can be an infinite time period.
b
Purge is determined by the ST7800 Purge Timing Card selected (RM7895 only).
PRINCIPAL TECHNICAL
FEATURES
The RM7890 and RM7895 Relay Modules provide 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 Operations
section.
b. Configuration jumpers are changed after 200 hours
of operation.
c. Four minute INITIATE period has been exceeded.
d. Purge card is not installed or was removed
(RM7895 only).
e. Purge card is faulty.
2. STANDBY PERIOD
a. Flame signal is present after 240 seconds.
b. Ignition/intermittent pilot valve terminal is powered
when it should be off.
c. Internal system fault occurred.
d. Main valve terminal is powered when it should be
off.
e. Three-second flame failure response time (FFRT)
amplifier is installed and configuration jumper is
selected for relight (RM7890); see Table 8.
f. Purge card is not installed or was removed
(RM7895).
g. Purge card is faulty.
3. SAFE START CHECK
a. Ignition/intermittent pilot valve terminal is energized
when it should be off.
b. Internal system fault occurred.
c. Main valve terminal is energized.
4. PREPURGE PERIOD (RM7895 Only).
a. Airflow lockout feature is enabled and the airflow
switch does not close after ten seconds or within the
specified purge card timing.
b. Flame signal is detected after 30 seconds.
c. Ignition/pilot valve/intermittent pilot valve terminal is
energized when it should be off.
d. Main valve terminal is energized when it should be
off.
e. Internal system fault occurred.
f. Purge card is not installed or was removed.
g. Purge card is faulty.
5. PILOT FLAME ESTABLISHING PERIOD (PFEP).
a. Ignition/intermittent pilot valve terminal is not
energized.
b. Internal system fault occurred.
c. Main valve terminal is energized when it should be
off.
d. No flame present at end of PFEP.
e. Airflow lockout feature is enabled and the airflow
switch opens (RM7895).
f. Purge card is not installed or was removed
(RM7895 only).
g. Purge card is faulty (RM7895 only).
6. RUN PERIOD.
a. Ignition terminal is energized when it should be off.
b. Internal system fault occurred.
c. Main valve terminal is not energized when it should
be on.
d. No flame is present and configuration jumper is
selected for lockout.
e. Pilot valve terminal is not energized.
f. Airflow lockout feature is enabled and the airflow
switch opens (RM7895).
g. Purge card is not installed or was removed
(RM7895 only).
h. Purge card is faulty (RM7895 only).
SAFETY PROVISIONS
Internal Hardware Status Monitoring
The RM7890; RM7895 Relay Modules analyze the integrity of
the configuration jumpers and internal hardware. The RM7895
checks the purge card for correct parity to prevent purge
timing shifts and circuitry failures. 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— that is, the main valve terminal is powered during
STANDBY— the relay module locks out on safety shutdown.
The relay module 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 noises 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
TM
Circuitry
Dynamic AMPLI-CHECK
TM
circuitry tests the flame signal
amplifier during burner operation and shuts down the relay
module if the flame amplifier fails.
Device Initiate Standby
a
Purge
b
Pilot Flame Establishing Period Run
a
RM7890 10 sec. — N/A 4 or 10 sec. —
RM7895 10 sec. — — 4 or 10 sec. —