HEIDENHAIN ND 231 B v.2 - Manual (Page 6)

6
Scale in
linear encoder
Distance-coded
reference marks
Position Encoders and Reference Marks
The ND 231 B display unit is intended for use with photo-
electrical linear encoders with sinusoidal signals: primarily
for HEIDENHAIN
MT length gauges with 11 µA
PP
.
These length gauges have
one reference mark. The scales of
other photoelectric linear encoders (see “Linear Encoders”) can
contain one reference mark or several
distance-coded refer-
ence marks.
If there is an interruption of power, the relationship between the
position of the length gauge and the displayed position value is
lost. The reference marks on the position encoders and the REF
reference mark evaluation feature enable the display unit to
quickly reestablish this relationship again when the power is
restored.
When a reference mark is crossed over, a signal is generated
which identifies that position as a reference point. At the same
time, the display unit restores the relationship between length
gauge position and display values which you last defined by
setting the datum.
If the linear encoders have
distance-coded reference marks,
you need only traverse a maximum of 20 mm to restore the
datum (for a signal period of 20 µm).
Reference mark
Reference marks on linear encoders
Position Encoders and Reference Marks