Schwank SET - SETU Owner's Manual page 57

CHANNEL MICRO 50N DSI: SEQUENCE OF OPERATION
The MICRO 50N is a three trial ignition control module with a 30 minute soft lockout/reset. It is
powered through a safety control circuit by a 24v transformer that is activated when the thermo-
stat calls for heat. On every call for heat the MICRO 50N will delay start-up with a 30 second
system pre-purge. After pre-purge an electronic generator powers the spark igniter and retrial/
safety lockout timing begins. At the same time, the gas control valve is opened allowing gas to
flow to the burner.
The MICRO 50N Control Module performs the following basic functions:

Provides a 30 second system pre-purge

Supplies power to the electronic pulse-generator circuit for the spark igniter (30,000 volts
open circuit).

Allows up to three 20 second trials for ignition before a 'soft' system safety lockout of 30
minutes occurs.

Three time trial for ignition and soft 30 minute lockout repeat

Senses the burner flame for flame maintenance

Shuts off the spark sequence after flame is established
Burner operation sequence:
1a. Line Voltage Thermostat: A call for heat by the line voltage Thermostat or an "ON/OFF"
switch, powers the blower and 120/24 volt Transformer simultaneously ... continue to 2.
1b. 24 Volt Thermostat: NOTE: Requires Optional Relay Kit JS-0568-KT - field installs in
burner for 24V thermostat control of a single heater. Multiple heaters per 24Vac thermostat
require optional Control Center JM-0303-KT (see previous page).
The 120 Vac supply to the burner simultaneously provides power to a 120/24V transformer
and the 120V terminal of a relay switch (open). When the 24 Vac thermostat calls for heat
the coil of the 24/120 volt relay switch is energized and closes 120Vac to the blower.
2. 24 Vac is provided to the proving air switch. The blower air supply creates a positive pres-
sure and closes the normally open proving air switch, closing 24 Vac to the normally closed
blocked flue switch.
3. Provided there is no blockage in the system (tube and vent), the blocked flue switch remains
in a normally closed position.
5. 24 Vac is supplied to the DSI control and the 30 second pre-purge cycle is initiated.
6. After completing the 30 second pre-purge cycle, the DSI control generates high voltage to
the spark igniter, and 24 Vac to energize the Gas Valve.
7. The burner ignites and establishes a steady flame.
8. Once the flame sensor (part of the spark igniter) determines there is a steady flame estab-
lished, with a minimum flame signal of 1.5 µA to the control, ignition spark is de-energized.
9. In the event ignition does not occur, the DSI control will retry the ignition sequence up to an
additional two trials. If ignition does not occur after the third ignition trial, the system will enter
a 30 minute 'soft' lock-out. This will reset the ignition module and the operating sequence will
restart at step #1 after the 30 minute soft lock-out period.
10. If there is a loss of flame during the run mode, the unit will energize the spark within 0.8 sec-
onds and perform a trial for ignition without the gas valve being closed first (Spark Restora-
tion). If a flame is not established during Spark Restoration the unit will repeat the process in
step number 9 (above).
57
SET(U)-F / ITT(U)-F Manual
IM091221
RD: FEB 2014
RL: 8B