Servomotor Type SQN 3...
dreizler A 3001 E - 18.12.2015 | A 2026 - 2.14 | EN - 11.11.2014
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The following drawings show the allocation of the switching cams of servomotor SQN 3... on the example
SQN 30.402 anti-clockwise rotation model in delivery condition ex works.
Tab. 17-1 Example: Setting the switching cams for SQN 30.402 anti-clockwise rotation
17.3 Description of the control process in burner operation
1) Pre-venting
The servomotor is controlled via the automatic gas control box. The burner runs with cam I to 'Air fully
opened' (90° opened), and provides throughput switching for the automatic gas control box.
2) End of pre-venting
The servomotor runs back and looks for the throughput impulse from cam III (e.g. at 40°). The cam has
been configured in such a way that it supplies a switching impulse when the servomotor is activated (or
cam II ends activation at 0° position).
3) Ignition phase
The servomotor has been moved by cam III into a position, in which the ignition transformer ignites.
The main gas solenoid valve is opened, gas is supplied.
4) Burner operation
During burner operation, the running angle of the servomotor is limited by cam I at full load and by cam
II at partial load. Depending on the position of these cams, the servomotor is set at a running angle in
between.
NOTICE:
Cam III can ignite the burner at a larger angle (e.g. 40°) than cam II (more gas at ignition). Cam III
should not be used where that is not desired (cam III must then be depressed - MIN load).
The switching roller of the servomotor and with it the air damper can be moved electrically, or uncoupled
from the gear box after depressing the locking bolt, and then moved or set manually.
Switching position cam I at MAX (full load)
Limit switch switches at MAX load 90° between 1
and 3 to throughput.
Switching position cam II at MIN (small load)
Limit switch switches at MAX load 30° between 2
and 4 to throughput.
Switching position cam III at ignition load
Limit switch switches at MAX load 40° between 8
and 9 to throughput.
