Siemens SIDOOR AT40 System Manual page 237

4. Tension the toothed belt with the aid of the tensioning device.
Check the belt tension by pressing the toothed belt inwards in the center.
You will recognize the correct belt tension by how far the belt is pressed in (B). The depth
(B) the belt is pressed in depends on the distance between the drive pinion and deflector
pulley (A).
The following depths of the pressed-in belt (B) apply as a function of the distance
between the drive pinion and deflector pulley (A).
AT40, ATD400V, ATD400K, ATD4xxW, ATD400S, ATE250S, ATD400T
System Manual, 06/2016, A2B00096162-AN
A (cm) 50
B (cm) 1.5
100 150
3 4.5
Geared motors
7.2 Installation
200
6
237