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Abstract
A single‐wavelength liquid signature analyzer can only reveal a part of the characteristics of some liquids, because the same liquid has different absorption in the light signal with different wavelengths and different liquids have different absorption in the light signal with the same wavelength. So dual‐wavelength light signals from two LEDs are introduced into the liquid drop. In the processing circuit, two light signals are modulated with different high frequencies. The collected signal is separated by band‐pass filters and demodulated by a linear precision demodulation circuit. Bubbles make the drop shape and volume become unstable, so a seal cavity is specially designed. The drop sensor is separable, thus, the drop head can be cleaned thoroughly, which reduces the mutual interference among different tested liquids. The penetration depth of fibers into the liquid drop can be adjusted quantitatively. Furthermore fibers, diodes, and the preamplifier circuit are integrated into the liquid drop sensor to reduce the serious loss of light intensity in transmission and the interference on the weak output signal. The experimental graphs of dual‐wavelength light signals and liquid drop fingerprints of different liquids are presented. The influence of the fiber position on the liquid drop fingerprint is studied.