When measuring electrical quantities in electrical engineering, we often encounter problems due to the presence of noise, which represents random and undesired disturbances in the signal. Even with highly engineered circuits and the use of quality components, complete elimination of noise is impossible. At the very least, thermal noise, which is caused by the thermal motion of charge carriers in materials, will always remain.
A Lock-in amplifier is a measurement instrument that uses the method of phase-sensitive detection (PSD) to isolate weak signals from dominant noise. Provided the frequency of the target signal is known, the system enables accurate measurements of signals that would otherwise be difficult to distinguish using conventional techniques.
The objective of this thesis was to build a cost-effective lock-in amplifier for use in laboratory practices at the Faculty and to present and evaluate its performance through testing.
The development process included designing the electrical schematic, based on a circuit presented in the paper [1], which was expanded to support differential voltage signal and current signal measurements. We have added the option to adjust the phase shift of the reference signal. After selecting the appropriate components and the enclosure, we designed the PCB layout, followed by soldering, testing, and performing measurements.
The functionality of the lock-in amplifier was verified through an experiment measuring a low resistance in the mΩ range. The measurement was performed using a voltage divider consisting of one known and one unknown resistance. A differential voltage measurement was used. The results showed a deviation from reference measurements within 2,5 %, which is acceptable for educational use.
Despite the final cost being higher than initially planned, we succeeded in building a functional, affordable, and user-friendly lock-in amplifier that meets the accuracy requirements of an educational setting.
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