Advanced Lock-in Amplifier for Detection of Phase Transitions in Liquid Crystals
نویسنده
چکیده
Lock-in amplifier (LIA) is the most important and essential instrument in signal recovery in the presence of large amount of noise. In this paper an indigenously designed microcontroller based advanced lock-in amplifier is proposed. The lock-in detection is done by quadrature sampling method. It is designed to work for the frequency range of 10Hz to 100kHz. The microcontroller based lock-in amplifier recovers signal of very small amplitude buried in large noise very efficiently. The designed lock-in amplifier is applied for a photoacoustic spectrometer (PAS) to detect the phase transitions in liquid crystal. In the present study N-(p-n-pentyloxybenzylidene)-p-n-hexylaniline (5O.6) liquid crystal compound is used as sample. The phase transitions of 5O.6 liquid crystal are detected by the system. The secondary transitions which are not observed in differential scanning calorimeter (DSC) are also observed in the proposed system. The amplitude and phase variations of the sample during the temperature scanning are measured and displayed on LCD module. The temperature scanning rate is kept at 0.3 o C/min. The measured amplitude, phase and temperature information is sent to the PC, via serial port, for further data processing/analysis.
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