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BTL6-P510-M _ _ _ _ -E2/E28-KA _ _ /LA _ _
Magnetostrictive Linear Position Sensor – Rod Style
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Construction and function (continued)
3.2
Function
The BTL contains the waveguide which is protected by an
outer stainless steel tube (rod). A magnet is moved along
the waveguide. This magnet is connected to the system
part whose position is to be determined. The magnet
defines the position to be measured on the waveguide.
An externally generated INIT pulse interacts with the
magnetic field of the magnet to generate a torsional wave
in the waveguide which propagates at ultrasonic velocity.
The component of the torsional wave which arrives at the
end of the waveguide is absorbed in the damping zone to
prevent reflection. The component of the torsional wave
which arrives at the beginning of the waveguide is
converted by a coil into an electrical signal. The travel time
of the wave is used to calculate the position. The position
value corresponds to the travel time of the torsional wave
and is output as digital time information between the start
and stop pulses.
The evaluation may relate to the rising or falling edge. This
is done with a high level of precision and reproducibility
within the measuring range indicated as the nominal
length.
INIT
Start
Stop
T
T
Fig. 3-2:
Time/distance measuring principle
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3.3
Principle
The P interface is a universal impulse interface and unifies
the functions of the falling and rising edges. The position
measuring system control is done via Init and start/stop
signals. Here, the "start pulse" is the reference point for the
travel time measurement.
Reliable signal transmission, even with cable lengths of up
to 50 m between the evaluation unit and BTL is ensured by
the particularly fail-safe RS485 differential driver and
receiver. Interfering signals are effectively suppressed.
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