Issue
132 Jult 2001
Inductive Sensors
by
George Novacek
Start
•
LVDT Revisited • The
Works • Electrical
Interfaces • Mechanical
Interfaces • The
Future • Sources &
PDF
MECHANICAL
INTERFACES
The pickup coils
need to see moving teeth or slots to detect motion and
determine position and speed. The coils’ geometry
is optimized for 0.040² (1 mm) teeth or slot width and
1-mm pitch between them. This will provide a 50% pulse
duty cycle. The sensor does not need to touch the target
and will work well with a 0.020² to 0.035² (0.5 to 0.9
mm) gap.
As you expect,
sensing a wheel’s teeth isn’t the only way to
use the sensor. You can, for example, use it to detect
presence (or absence) of a metallic target or movement
of a slot into a predetermined position. In such applications,
the CSEM sensor wouldn’t be much different from proximity
sensors. And proximity sensors are widely used as limit
switches or position detectors. Such switches detect position
of the thrust reverser transcowls in jet engines or down-and-locked
position of a landing gear, where even the best sealed
mechanical switch has a limited life.
Another interesting
way of detecting position is shown in Photo 3, which is
a demonstrator kit available from CSEM. Instead of having
teeth on the circumference of the wheel, the wheel has
been threaded. So, in effect the sensor sees only one
tooth moving across its sensing window as the wheel turns
and makes one revolution. This provides you with absolute
position measurement of the rotational angle. The interpolation
breaks up the 360° of rotation to 256 chunks of 1.4° of
angular movement. With standard bandwidth the sensor will
work up to 9,000 rpm.
 |
| Photo
3—The
CSEM demonstrator kit has a thread instead of teeth. |
