KROHNE BM 26 A EN - Manual (Page 33)

Installation and Operating Instructions BM 26 A 33
3.6 Fine adjustments to the limit switch trigger point
3.6.1 General
notes
Due to the way the reed switch switches from one state to another and the geometry of magnets
integrated into the float, different switching points are obtained when the float moves up or down.
This must be taken into account when positioning the limit switch.
The assembler must equally remember that as with the local display, limit switch position must take
into account the fact that indicated level is lower than true level.
By default, indicated level is lower than true level by “b” mm. This should be adjusted during
commissioning (see section 1.6.4). When the float moves up, the switch is triggered with the float
offset by “d” mm. When the float moves down, the switch is triggered with the float offset by “e” mm
(see section 3.6.3).
Hysteresis: see section 7.3.
3.6.2 Fine adjustments to the limit switch trigger point
Step Action
1
Choose the true level at which the limit switch should signal “limit reached“.
2 Adjust the switch position using the procedure in Section 1.6.4 to take into account the
difference between true liquid level and indicated level (magnet position). Move switch down
measuring tube by “b” mm.
3 Refer to the table in section 3.6.3: “Switching point offsets“. Find the limit switch offset based
on the limit switch type and the direction in which the float is moving for the switch to be
triggered. Example: if the switch has to trigger when the float moves upwards then a MS
15/STD switch needs to be moved down the measuring tube by 5mm or 0.2 ”.
4 Loosen the collar holding the limit switch onto the measuring tube.
5 Now re-position again to take into account the switch trigger points -Move the switch up or
down the measuring tube by the amount required for the offset as indicated in the table and
drawing in section 3.6.3.
6 Retighten the collar holding the limit switch onto the indicator tube.