Linear Variable Differential Transformer Design and Verification Using MATLAB and Finite Element Analysis

The linear variable differential transformer is one of the most widely used transducers for measuring linear displacement. It offers many advantages over potentio-metric linear transducers such as frictionless measurement, infinite mechanical life, excellent resolution and good repeatability (Herceg, 1972). Its main disadvantages are its dynamic response and the effects of the exciting frequency. General guidelines regarding the selection of an LVDT for a certain application can be found in (Herceg, 2006). The LVDT is also used as a secondary transducer in various measurement systems. A primary transducer is used to convert the measurand into a displacement. The LVDT is then used to measure that displacement. Examples are: 1. Pressure measurement whereby the displacement of a diaphragm or Bourdon tube is detected by the LVDT (e.g., diaphragm type pressure transducer, (Daly et al., 1984)). 2. Acceleration measurement whereby the displacement of a mass is measured by the LVDT (e.g., LVDT used within an accelerometer, (Morris, 2001). 3. Force measurement whereby the displacement of an elastic element subjected to the force is measured by the LVDT (e.g., ring type load cell, (Daly et al., 1984)). The classical method of LVDT analysis and design is based on the use of approximate equations as shown in (Herceg, 1972) and (Popovic et al., 1999). These equations suffer from inaccuracy especially from end effects. More novel methods for design employ finite element methods (Syulski et al., 1992), artificial neural networks (Mishra et al., 2006) and (Mishra et al., 2005). The dynamic response of the LVDT is discussed in (Doebelin, 2003). The LVDT has also been integrated into linear actuators (Wu et al., 2008).