Study of a Modified LVDT Type Displacement Transducer With Unlimited Range

The conventional LVDT is generally used as displacement transducer but has some limitations such as small linear range, measurement errors due to stray capacitance effect, electromagnetic interference effect, and core loss effect. In this paper, a modified LVDT type displacement transducer has been proposed in order to overcome these limitations of conventional LVDT. The proposed LVDT will consist of only two identical coils instead of three coils of conventional LVDT. This design does not require any excitation coil. In this design, two identical coils wound on a former made of ferromagnetic material act as displacement sensing inductive coils with specially designed movable core. The design has been analyzed under three cases. It has been shown that the range of the displacement transducer is about 50% of the overall length of the sensor under two cases like conventional LVDT and is about 100% of the overall length of the sensor under the third case. So in this paper, a displacement transducer has been designed and tested experimentally considering only the third case with unlimited range equal to the entire length of the sensor. The transducer consists of an op-amp-based differential inductance measuring circuit and an output instrumentation amplifier. The performance equations of this sensor under three cases and of the transducer under third case are derived in the paper. The experimental results reported in the paper are found to follow the derived equations with very good linearity and repeatability.