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OPERATION
TYPICAL FURNACE INSTALLATION
In a typical system, a call for heat is initiated by closing the
thermostat contacts. This will energize the 50E47 control.
If the system is equipped with prepurge, the prepurge fan
or interfacing relay is also energized through the thermo-
stat contacts. In the prepurge mode, the 50E47 control will
delay 30 seconds before applying power to the 767A
silicon carbide ignitor. If prepurge is not an option, the
ignitor is powered within one second.
The ignitor is then allowed to warm up for 17 or 45 seconds
depending on the 50E47 control dash number being used
(see Timing Specifications table). Various ignitors on
the market must use the 45-second option to allow them
to fully attain ignition temperatures at low voltage condi-
tions. The W-R 15-second ignitor is especially designed
to heat up quickly at a low voltage condition without
overheating at a high voltage condition. Thus, the W-R 15-
second ignitor may also be used with a 45-second warm-
up time without detrimental effects.
At the end of the ignitor warm-up time, both valves in the
36E manifold gas valve are opened. The ignitor will
remain on for an additional one second (ignition activation
period). A four-second ignition activation period is also
available. Flame must be detected within four seconds (a
seven-second trial for ignition period is available as a
separate type). If flame is not detected, both valves are
de-energized, the ignitor is turned off, and the 50E47
control goes into lockout.
If the control is locked out, it may be reset by momentary
power interruption of
1
⁄20 second or longer. Either the
24 volt thermostat or line voltage may be interrupted.
The 50E47 control may also be equipped with a retry
option, depending on the dash number (see Timing
Specifications table). This provides a 60-second wait
following an unsuccessful ignition attempt (flame not
detected). If the prepurge option is used, the waiting time
becomes 90 seconds (30-second prepurge plus 60-sec-
ond wait).
After this wait, the ignition sequence is restarted. An
additional 10 seconds is added to the ignitor warm-up
time, so a module with a 17-second warm-up time will
have 27 seconds of ignitor warm-up or a module with a
45-second warm-up time will have 55 seconds of ignitor
warm-up. If this ignition attempt is unsuccessful, one
more retry will be made before lockout.
All 50E47 controls will repeat the ignition sequence for a
total of five recycles if flame is lost within the first 10
seconds of establishment.
If flame is established for more than 10 seconds after
ignition, the 50E47 controller will clear the ignition attempt
(retry) counter. If flame is lost after 10 seconds, it will
restart the ignition sequence. This can occur a maximum
of five times.
During burner operation, a momentary loss of power of 50
milliseconds or longer will de-energize the main gas
valve. When power is restored, the gas valve will remain
de-energized and a restart of the ignition sequence will
begin immediately.
A momentary loss of gas supply, flame blowout, or a
shorted or open condition in the flame probe circuit will be
sensed within 0.8 seconds. The gas valve will de-ener-
gize and the control will restart the ignition sequence after
waiting 60 seconds. Recycles will begin and the burner
will operate normally if the gas supply returns, or the fault
condition is corrected, before the last ignition attempt.
Otherwise, the control will go into system lockout.
If you need further information about this product, please write to
White-Rodgers Division, Emerson Electric Co.
9797 Reavis Road
St. Louis, MO 63123-5398
Attention: Technical Service Department