Characteristics And Function; Characteristics; Display Elements; Principle Of Operation - Balluff BML-S1A-Q/A-M-0-S184/KA Serie Manual De Instrucciones

BML-S1A_-Q/A_ _ _-M_ _ _-_0-S184/KA_ _
Linear Position Encoder
3

Characteristics and function

3.1

Characteristics

BML displacement sensors are
characterized by:
– High system accuracy of 10 or
20 µm
– High resolution of up to 1 µm
– High traverse speed of up to
20 m/s
– Position signal in real-time
– Very good non-linearity (up to
max. ±10 µm)
– Insensitive to shock, vibration,
and contamination such as dust
and oil
Wear- and maintenance-free
–
– Rugged
– Enclosure rating IP 67 per
IEC 60529
3.2

Display elements

The digital sensing head has an
LED fault indicator (at the front).
Flashing indicates that no signals
are being output, for example
because the distance between
sensor head and tape is outside the
tolerance.
3.3

Principle of operation

The sensing head is attached to the
machine member whose position is
to be determined, while the
magnetic tape is mounted along the
direction of travel. The tape
contains alternating magnetic north-
and south poles.
The two incremental sensors in the
sensing head measure the magnetic
alternating field.
As the tape is passed over without
contact, the entire underside of the
sensor head must always lie above
the tape. The two incremental
sensors in the sensor head pick up
the magnetic periods so that the
controller can determine the
distance traveled.
In order to be able to count knowing
the direction of travel, the two
incremental sensors are offset to
each other. The sinusoidal output
signals from the two incremental
sensors are phase-shifted by 90°
and 270° respectively and can be
interpreted as a sine and cosine
signal.
4
english
3.4

Interface signals

The sensing head can convert the
sinusoidal and cosinusoidal signals
either into A/B pulses and send
them to the controller (RS422), or
output the analog sine and cosine
signals directly. The signals are sent
as differential signals.
The digital A/B pulses are
interpolated in the sensing head,
whereas the analog signals must be
interpolated in the controller.
The two digital pulses A and B are
90° phase-shifted, with the sign
of the phase shift determined by the
direction of travel of the sensor
(Fig. 3-1).
Each edge change from A or B
represents a counting step for the
period counter (UP/DOWN counter).
Signal A
Signal B
Increment
Direction of motion
Example counter state
Fig. 3-1: Digitized sine and cosine signals with period counter
Output voltage
B (Cosine)
A (Sine)
Fig. 3-2: Signals from sine and cosine sensor with a magnetic period of 2 mm
(1 mm pole width)
When Signal A is ahead, the
counting state increases, and when
Signal B is ahead the count
decreases. The controller thus
always knows the increment-precise
position without having to
periodically poll the sensor (real-
time capability).
In the case of the analog sine and
cosine signals (sin+, sin–, cos+,
cos–) the controller evaluates the
difference in the signal amplitudes
and interpolates from the 4 signals
the exact position within one period
(Fig.. 3-2). If there is movement over
several periods, the controller also
counts the number of periods.
Note, for correct function the
A and B signals must be
evaluated direction-dependent.
Forwards Backwards
Travel µm