Page 456 - Sensors and Control Systems in Manufacturing

Sensors in Flexible Manufacturing Systems

FIGURE 8.31 Plot of LVDT operational characteristics. 409

When the primary coil is energized by an external AC source, volt-
ages are induced in the two secondary coils. These are connected
series-opposing so that the two voltages are of opposite polarity.
Therefore, the net output of the sensor is the difference between these
voltages, which is zero when the core is at the center or null position.
When the core is moved from the null position, the induced voltage
in the coil toward which the core is moved increases, while the
induced voltage in the opposite coil decreases. This action induces a
differential voltage output that varies linearly with core position. The
phase of this output voltage changes abruptly by 180° as the core is
moved from one side of the null to the other.

8.10.1 Extreme Environments
With increasingly sophisticated technology, more and more instru-
mentation applications have arisen for sensors capable of operating
in such hostile environments as extremely cold temperatures, very high
temperatures, and/or intense nuclear radiation. The LVDT has been
developed with materials that can tolerate extreme environmental