LVDTs (linear variable differential transformers) are electromechanical measuring devices that convert the position of a magnetic core into electrical signals. You generate these signals via excitation on the primary side. The results on the secondary side ―typically, two secondary windings―depend on the position of the core (Figure 1). The excitation typically ranges in amplitude from 1 to 10V and in fre-quency from 1 to 10 kHz, depending on the type of LVDT you employ. Traditionally, for one circuit to provide such variability in frequency and amplitude, you can use either an LC tank with adjustable components or a sine-wave generator under microcontroller control. It can be difficult to achieve precision over time and temperature with the LC-tank circuit because of variations in passive components. You also must manually perform calibration. You can more easily obtain precision over time and temperature through the use of a microcontroller-controlled sine-wave-generator chip, and calibration can be automatic, but the method incurs a greater expense than the LC-tank circuit. The circuit in Figure 2 presents an alternative.
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