Kaman KD-5100 - Manual (Page 6)

6
2. THEORY OF OPERATION
2-1. The KD-5100 Differential Measuring System uses advanced inductive measurement
technology to detect the aligned or centered position of a conductive target. Two matched
sensors are positioned relative to the target so that as it moves away from one sensor it moves
toward the other an equal amount.
2-2. The transducer operates on the principle of impedance variation caused by eddy currents
induced in a conductive target located within range of each sensor. The coil in the sensor is
energized with an AC current, causing a magnetic coupling between the sensor coil and the
target. The strength of this coupling depends upon the gap between them and changes in gap
cause an impedance variation in the coil.
2-3. In the KD-5100, the coils of a pair of sensors form the opposite legs of a balanced bridge
circuit (Figure 1).
VOLTAGE
REGULATOR
+15 Vdc
COMMON
-15 Vdc
Figure 1 Block Diagram: Differential Measuring System
2-4. When the target is electrically centered between the two sensors at the nominal null gap for
each, the system output is zero. As the target moves away from one sensor and toward another,
the coupling between each sensor and target is no longer equal causing an impedance imbalance
between the sensors. The bridge detects this imbalance and its output is amplified, demodulated,
and presented as a linear analog signal directly proportional to the targets position. This is a
bipolar signal that provides both magnitude and direction of misalignment. Only the differential
output is available.