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AI-TEK,
formerly Airpax Instruments, provides a complete line of;
tachometers, speed indicators, variable reluctance speed sensors,
magneto-resistive and Hall Effect Sensors to measure rotary
speed. |
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Here
to access detailed info on all products. |
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The internal construction of the typical AI-TEK variable
reluctance sensor is a magnet, pole piece and coil
(See Figure 1). A magnetic field (lines of flux) extends
from the magnet, through the pole piece and coil out
into the air space at the end of the sensor. The return
path of the magnetic field is from the air space to
the other end of the magnet. As a ferrous object approaches
the tip of the pole piece, the magnetic field increases
and then decreases as the object moves away from the
pole piece. The snap or the rapid change in the magnetic
field induces an AC voltage signal in the coil. With
an ideal target and matching sensor, the induced voltage
is in the shape of a sine wave. As can be seen, the
generated frequency signal is directly proportional
to the number of ferrous objects passing the pole
piece per unit time. The amplitude of the voltage
output is proportional to the speed of the ferrous
objects passing the pole piece. |
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Figure
1: Internal
configuration of typical sensors. |
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Figure
2: Common
terms used in defining gears. |
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Many applications
of AI-Tek magnetic sensors use gears as targets. Typical
sensor output wave forms with various targets are
illustrated in Figure 3. Testing sensors with gears
rather than other ferrous discontinuities such as
sprockets, keyways, boltheads, etc. is because the
output is predictable and repeatable. See Figure 2
for commonly used gear terminology. |
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The performance
of a sensor can be easily defined when using a gear
for a target; it also allows for estimated performance
with alternate targets. AI-Tek sensors are tested
with AGMA standard gears; the performance curves are
included in this catalog. AI-Tek Instruments differs
from most sensor manufacturers in the presentation
of performance curves and test parameters. Most existing
data is specified at a surface speed of 1000 in/sec
and 0.005 in. air gap; we feel that a 0.030 in. air
gap and 500 in/sec. surface speed (1800 RPM motor
with 5 to 6 in. dia. gear) are more realistic parameters
to specify performance. |
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Figure
3: Generated
voltage waveforms. |
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