CAE of Sensors and Actuators
Project 3
Magnetic Field: Linear Variable Differential Transformer (LVDT)
Show First Results: January 22, 2009,
Presentation of Results: Februrary 5, 2009.
Problem Description
A linear variable differential transformer (LVDT) is used to measure displacements. It
consists of a moveable core with coating and three coaxial windings (see Figure 1): The
center winding is the primary and the other two are the secondaries. When the the core and
ferromagnetic coating move, while an AC current excitation is applied to the primary coil,
the coupling between the primary and each of the two secondaries changes. As a result,
the output voltage magnitude changes when compared to the initial position.
Figure 1: Magnetic Linear Differential Transformer
Modeling and Analysis
In the setup above, the core is made of plastic. The surrounding coating layer is made of
iron. For the excitation coil, we have 100 windings, whereas the measurement coils have
each 50 turns. The material of the coils can be assumed to be of non-conductive copper to
suppress the creation of parasitic eddy currents.
• Setup the axi-symmetric assembly. Choose an appropriate distance to the outer
boundary of the calculation region (the sensor operates in air).
• Perform a static analysis with an excitation of 10 µA for the primary coil and calculate
the inductance L as can be seen from the connector ports 1 and 2.
• Now we consider a harmonic current with 1 kHz. Calculate the induced voltage U12
in the upper coil, for different positions z of the core.
CAE of Sensors and Actuators
Project 3
• Repeat the simulation from above, but now consider the two coils connected at ports
2 and 3 and calculate the induced voltage U14 .
• Calculate for both cases from above the sensitivity and the range zmin and zmax for
which the linearity error is smaller than 5%.
• Perform some variations on the setup: Change the thickness of the coating to 0.5 mm
and change the length of it to 6 mm. How does the sensitivity change?
Presentation
• Prepare for a 10 to 15 minute presentation (format: PDF (preferred) or MS PowerPoint)