A Study of Linear Variable Differential Transformers in MATLAB

The purpose of this lab was to test Faraday’s Law using a Linear Variable Differential Transformer (LVDT). Basically, an LVDT consists of three coils (of 100 windings each) spaced evenly along an insulating rod. A voltage of around 6 V was applied across the inner coil, and a ferromagnetic rod was inserted into the solenoids. According to Faraday’s Law, a changing magnetic flux within the ferromagnetic core will induce an output voltage in the outer coils. Due to the winding reversal between the coils though, the induced voltage will be opposite. Thus, a zero point (where the induced voltages cancel out) can be found using MATLAB’s softscope oscilloscope function. Furthermore, as the core is moved linearly between the windings, a linear shift from a negative voltage to a positive voltage can be found. This linear fit is caused by changes in the exterior windings enclosing the core, and a linear function can be found to describe this phenomenon using MATLAB’s polyfit command, which generated a slope of 6.5 mV per cm. A voltage decrease at the LVDT’s ends can be attributed to the core partially leaving the inner coil. In conclusion our data agreed with the theory, but small changes-such as a longer core-could have generated less error and produced a stronger linear fit.