Servomotor Type SQN 7...
dreizler A 3001 E - 18.12.2015 | A 2025 - 2.14 | EN - 11.11.2014
52
The following drawings show the assignments of the switching cams of servomotor SQN 7... on the exam-
ple SQN 70.664 A 23 anti-clockwise rotation model in delivery condition ex works.
Tab. 16-1 Example: Setting the switching cams for SQN 70.664 A23 anti-clockwise rotation
16.3 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°). This cam is
set to provide a switching impulse when the servomotor is activated (or cam II ends motor activation at
O° 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.
Switching position cam I at MAX (full load)
Limit switch switches at MAX load 90° between 1
and 5 to throughput.
Switching position cam II at MIN (small load)
Limit switch switches at MIN load approx. 30°
between 2 and 5 to throughput.
Switching position cam III at ignition load
Limit switch switches at ignition load at 40°
between 4 and 5 to throughput.