|
|
|
LVTs are kinds of
speed sensors which are usually used to measure the speed of small
motions.
|
Linear
Velocity Transducers use inductive technology. Moving a magnet
through a coil of wire will induce
a voltage in the coil according to Faraday's and Lenz' Laws.
This voltage is proportional to the magnet's velocity and
field strength. LVTs use this principle of magnetic induction,
with a permanent magnet and a fixed geometry coil, so the
output voltage of the coil is directly proportional to the
magnet's relative velocity over its working range.
During operation in the working range of the transducer, both
ends of the magnet are inside the coil. With a single coil this
would give zero output because the voltage generated by one pole
of the magnet would cancel the voltage generated by the other
pole. To avoid this, the coil is divided into two sections, so
the N (North) pole of the magnet will induce a voltage in one
coil and the S (South) pole will induce a voltage in the other
coil. These two coils are then connected in series-aiding, to
obtain a DC voltage output proportional to the magnet's
velocity.
|
Coils in Series
For series
operation, the blue and green leads are tied together
and the output is taken from the black and red leads.
With the coils wired in series, the output is summed,
producing the maximum sensitivity. Besides a high
sensitivity, the transducer exhibits excellent noise
immunity, attributed to the coils being wound in series
opposition. Noise generated on one coil will be equal in
magnitude but opposite in polarity to the other coil.
|
|
|
Coils in Parallel
Parallel
operation is achieved by tying the black and blue leads
together, and the green and red leads together. The two
connections create the terminals for the output. This
configuration cuts the sensitivity in half, and reduces
the source impedance by a factor of 4. The benefits of
this arrangement are: lower output, for use in high
speed applications; lower output impedance, for
compatibility with electronics with a low input
impedance, and higher frequency response for a given
load impedance. |
|
|
Major manufacturers of LVTs are
Trans-Tek Inc. and GE Company.
The working displacement ranges are
from 0.5 in. to 24 in., and typical sensitivities are from 40 mV/ips
(inches per second) to 600 mV/ips.
The series100 LVTs are the most popular ones; produced by Trans-Tek .The Series 100 Linear
Velocity Transducers are inductive, instantaneous velocity
transducers. By moving a magnet through a pair of series opposed coils,
the transducer will output a DC voltage proportional to the
instantaneous velocity. No excitation voltage is required. Available
ranges are from 0.5" to 24.0".
You can review Series100's data sheet
here.
Main Features of series100 :
Measurement Ranges
: 0.5 to 24 inches
Maximum Non-Linearity
: 2.5% Full Scale
Housing Outer Diameter
: varies
Operating Temperature Range : -65°F to
+140°F
Sensitivity
: Up to 500 mV/inch/second
Excitation Voltage
: None required
Two other models of LVTs, produced by GE company are models 9200 and
74712.For information in details, review them on their
data sheet.
Some of other manufacturers are Robinson-Halpern
Products and Macro sensors.
|
