LINEPULS & LINECOD catalogue 2016 in English

LINEPULS • LINECOD
Technical information
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Linear sensors are equipped with high-flex cables especially suited for use in cable drag
chains and tested for more than 1 million cycles. Furthermore they are expressly designed for
high speeds up to 10 m/s and accelerations up to 6 m/s 2 . They are halogen free and resistant
to oil, hydrolysis and abrasion. For more details please refer to page 118.
When choosing an encoder model, please consider the noise and the cable length that could
affect the system and reduce its performances. Longer cable lengths are more susceptible to
noise. It is crucial to use proper cable lengths to ensure that the system operates correctly.
We recommend shielded, twisted-pair cables to be used. For more information on the cable
lengths recommended for each interface please refer to the specific sections.
Cables
The magnetic tape is magnetized in order to have a sequence of North and South poles
along the path. The poles allow the magnetic sensor passing along the tape to detect the
changes in the magnetic field, that is to sense each small shift in the position and so to
output a signal in response to motion.
The pole pitch is the distance between two consecutive poles and is expressed in millimetres.
Pole pitch
In an incremental measuring system the tape has a systematic sequence of North and
South poles. The pole pitch depends on the magnetization process and tapes with a variety
of pole pitches can be supplied. MT10 magnetic tape, for instance, provides 1.0-mm pole
pitches, while MTS25 magnetic tape provides 2.5-mm pole pitches. The smaller the pole
pitch, the higher the resolution and the quality of the positional information.
The incremental pole pitches can be 1, 2, 2.5, 3.2, 4 and 5 mm long, according to models.
In an absolute measuring system, the absolute coding pole pitch depends on the physical
characteristics of the sensor array deployed in the sensing head. The smaller is the distance
between the sensors in the array, the smaller is the pole pitch. In an absolute measuring
system the tape has a sequence of alternating magnetic fields, but they have different dimensions
(more than one either North or South pole could follow in the sequence).
You must always pair the encoder with the right pole pitch tape.
For instance, the SME1 linear encoder must be compulsorily paired with the MT10 tape.
If otherwise, the sensor cannot work.
The resolution can be defined in several
ways. It is the ability to provide the information
over a defined space; otherwise
it is the spacing between two consecutive
discrete points, i.e. the sequence of
information. The more discrete points are
used and the smaller the distance between
these points, the higher will be the resolution
of the measurement system and the
quality of its information.
When referring to an incremental linear
encoder, the resolution (otherwise referred
to as “measuring step” or “measuring
increment”) is the distance between two
following edges of A and B channels. It results
from the pole pitch of the magnetic
tape and the interpolation factor. It is indicated
by using a metric length such as
millimetres (mm) or microns (μm). Digital
linear incremental encoders interpolate the
analogue sine/cosine signals by an interpolation factor in order to sub-divide the tape period,
so providing a higher measurement resolution. The output of the interpolation process
results in quadrature squarewaves – the distance between the edges of the A and B channels
being the resolution of the encoder. Unlike what is stated in rotary encoders, the resolution
indicated in this catalogue for the linear incremental encoders is always to be intended
after quadruplication, as shown in the Figure.
Resolution
In an absolute encoder the resolution can be defined as the smallest change in the underlying
physical quantity that produces a response in the measurement, the response being
the absolute information that is provided to output.
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