11
Caution!
The microswitches used in the individual units do not allow two voltages of different values or phases to be applied to
contacts of the same microswitch. Thus, they can be used as a switch, cut-out or change-over switch for a singlecircuit only.
For control of the actuator at the site of installation, deblocking device consisting of deblocking switch and local
control switch can be fitted, if required.
Block of local control consists of two change-over switches. One is used to switch between remote and local control,
the second is used to open or close the valve when the first switch is set to local control. Both change-over switches are
part of the terminal box. Change-over switch local / remote control can be locked with a padlock against unauthorized
manipulation (padlock is included in the delivery).
Description and functions of control units
a) The torque-limit switching unit (Fig. 3)
-
forms an independent assembly group consisting of the base plate 19 which carries microswitches 20, while at
the same time providing for bearings of the torque control shaft 22 and the locking shaft 29.
The torque control shaft transmits movements of the floating worm from the power transmission gear to the CLOSE
torque-limit microswitch
(MZ)
or the OPEN torque-limit microswitch
(MO)
by means of segments 23 or 24 and levers 45 or
46. The amount of limit-switching torque and thus indirectly even the axial force on the actuator pull-rod can be adjusted
by the segments being turned with respect to the tripping levers. For readjusting the amount of the tripping torque outside
the factory, the segments 23 are provided with a scale on which the points of adjusting the maximum and minimum
torques have been marked red individually for each actuator, the adjusted torque being indicated by slots in the segments
27 and 28. However, the numbers on the scale provide no direct indication of the tripping torque adjustment, but the scale
divisions serve only for a more accurate division of the band between the points of maximum and minimum tripping
torques and thus for more accurate adjustment of the torque outside the factory in a location where no test stand is avai-
lable. The segment 23 is designed for the CLOSE direction, whereas the segment 24 is designed for the OPEN direction.
The torque control unit is also fitted with a locking mechanism. On operation of the torque-limiting switch, thismechanism
locks this switch and thereby precludes the switch from being reclosed unprompted and thus prevents the actuator from pul-
sing. Moreover, the locking mechanism prevents the torque-limit switch from opening after reversal of the actuator.
The locking mechanism acts in either direction of the output shaft motion of the actuator in the end positions as well as in the
intermediate position for the duration of 1 to 2 revolutions of the output shaft after reversal thereof. With the output shaft of the
actuator loaded at a reversed torque, the torque control shaft 22 and thus the segments 23 and 24 turn by a slight amount.
From the segments, this displacement is transmitted to the tripping lever 45 or 46. When the torque on the output shaft of the
actuator reaches the value to which the torque-limit switching unit has been adjusted, the tripping lever depresses the button
of the corresponding microswitch so that the electric motor is disconnected from the mains, thus stopping the actuator.
Adjusting procedure of the torque-limit switching unit
To adjust a different tripping torque from that adjusted at the factory, the procedure is the following: Loosen the lock
nut 44
(see Fig. 3)
and then the lock screw 25
(for the CLOSE direction)
or 26
(for the OPEN direction).
Place
a screwdriver in the slot of the upper segment 23 or 24 and turn the segment till the slot in the segment 27 or 28 tallies
with the respective scale graduation line. This scale division line can be determined so that the difference
(in Nm)
between the maximum and the minimum adjustable torques is divided by the number of divisions between the marks of
19
20
29
21
23
25
27
45
22
44
24
26
28
46
12
10
13
11
Fig.3 -
Torque-limit switching unit
Diagram
of microswitches
Legend:
19 – Base plate
20 – CLOSE and OPEN
torque–limit switches
(MZ, MO)
21 – Shifter
22 – Torque control shaft
23 – Upper CLOSE segment
24 – Upper OPEN segment
25 – CLOSE lock screw
26 – OPEN lock screw
27 – Lower CLOSE segment with slot
28 – Lower OPEN segment with slot
29 – Locking shaft
44 – Lock nut
45 – OPEN tripping lever
46 – CLOSE tripping lever
The encircled numbers correspond
to the numbers of terminals
on the terminal board of the actuator.
The microswitches can be used
as one-circuit devices only.
