Resumen de Low-Cost, High-Performance Lock-in Amplifier for Pedagogical and Practical Applications
Xicheng Xu, Yoshinori Suganuma, Al-Amin Dhirani
Lock-in amplifiers (LIAs) are commonly used in chemistry laboratories to improve noise-to-signal ratios. Constructing and testing a suitably designed LIA provide undergraduate students with an excellent opportunity to learn about theory, construction, and applications of LIA. In particular, students can learn about time-dependent behavior and various components, from resistors (R) and capacitors (C) to packaged microchips such as demodulators and phase shifters. We provide here design and performance characteristics of a two- (Vx, Vy) channel LIA based on balanced modulator/demodulators (AD630). The LIA includes configurable resistor–capacitor (RC) high-pass and low-pass filters, various op-amp circuits, and a phase-shifter. Various configurations of resistors/capacitors, as well as salt solutions and isopropanol/pentane mixtures, are used as samples to measure conductance or capacitance to test both Vx and Vy channels of the LIA. The results are consistent with behaviors expected theoretically. The LIAs yield excellent noise/signal ratios with peak-to-peak values that are <0.2% and that compare favorably with commercial LIA performance.
