Automating Manufacturing Systems - Process Control and ...

discrete sensors - 4.24
metal
inductive coil
+V
oscillator
and level
detector
output
switching
Note: these work by setting up a high frequency field. If a target nears the field will
induce eddy currents. These currents consume power because of resistance, so
energy is in the field is lost, and the signal amplitude decreases. The detector examines
filed magnitude to determine when it has decreased enough to switch.
Figure 4.27
Inductive Proximity Sensor
The sensors can detect objects a few centimeters away from the end. But, the
direction to the object can be arbitrary as shown in Figure 4.28. The magnetic field of the
unshielded sensor covers a larger volume around the head of the coil. By adding a shield
(a metal jacket around the sides of the coil) the magnetic field becomes smaller, but also
more directed. Shields will often be available for inductive sensors to improve their directionality
and accuracy.