Why LVDT called secondary transdsucer?

An LVDT (Linear Variable Differential Transformer) is called a secondary transducer because it converts a mechanical displacement into an electrical signal. While primary transducers convert physical quantities (like pressure or temperature) into mechanical movement, LVDTs specifically measure that movement and output a proportional electrical signal. This differentiates it from primary transducers, as it relies on the input from another system to generate its output.