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To achieve the aim of precise measurement of a target micro‐sphere, approximately 0.2 mm in diameter, a laser confocal probe was designed. To improve the output signal, a mathematical model of the photoelectric signal was proposed. The diameter of the pinhole was determined, and the optical path was adjusted; the oscillating units were designed. The performance of the probe was validated by experiments using gauge blocks combined with a micro‐motion measuring mount model. Besides, a more accurate signal processing method was suggested.

The liquid drop fingerprint (LDF) can be obtained from fiber‐capacitive drop analysis. LDF is unique and specific for a certain liquids. LDF makes the time‐based fiber drop trace independent from the speed of drop growth and the volatility of liquids. Identification and linear interpolation are used to normalize the fingerprint data, to make LDFs of different liquids comparable. A correlation comparison method is used to describe LDF quantitatively, by using the geometric correlation coefficient, the vector correlation coefficient, the scale correlation coefficient, and the distance correlation coefficient. The mathematical correlation functions are introduced in detail. Some experimental graphs and data results are presented.

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 ...

Fiber drop analysis reveals the variation regularity of the light signal passing through the liquid drop during the drop growth. The coupled light signal reflects mechanical and optical properties of the tested liquids, but it is not only dependent on the profile and volume of the drop, but it is also dependent on the liquid absorption. Thus, spectral drop analysis is introduced into the drop analyzer to study the liquid composition by studying the absorption spectrum of the multi‐wavelength light signal passing through the liquid. A three‐dimensional (3‐D) liquid drop fingerprint (LDF) can be obtained by merging the light intensity signal from the fiber drop sensor, the drop volume signal from the capacitive drop sensor or CCD image processing, and the absorption spectrum signal from the fast Fourier transform (FFT) infrared spectrum analyzer. The 3‐D LDF covers a more extensive range of physical and chemical properties of liquids, and it enhances the capability of drop analysis for fine discrim...

An instrument called the liquid signature analyzer (LSA) has been developed for liquid property studies. The LSA is based on fiber‐capacitive drop analysis and produces a liquid drop fingerprint (LDF) which shows the variation of the coupled light signal inside the drop along with the drop formation. The LDF reflects multiple properties of the tested liquids and it is unique under certain conditions. A fiber‐capacitive drop sensor is designed through which a satiated and uniform drop is formed. A micro‐flow feeding pump, actuated by a single stepper motor and controlled by the computer software, is devised to ensure that the drop is slowly delivered under quasi‐equilibrium conditions. Modulation and demodulation are used to exclude the possible influence of ambient light in the fiber signal processing circuit. Three methods are presented in capacitive signal measurement; they are frequency modulation, differential frequency method, and transformer bridge method. A computer interface for the LSA h...

A photoelectric multiple‐wavelength liquid drop sensor (PMWLDS) is introduced in this paper. Being employed in the liquid signature analyzer (LSA), the PMWLDS has improved much of LSAs characteristics, compared to the previous models. The PMWLDS is constructed of two integrated parts and can be separated during its cleaning. When separated, all the surfaces contacting liquid samples become open surfaces, by which the liquid head can be cleaned easily. A small chamber is designed for the elimination of the bubbles existing in the test liquid. Otherwise, the unique drop forming process will be destroyed and the LSAs test results will become meaningless. Due to a multiple‐wavelength light source integrated into the sensor, liquid drop traces can be obtained based on different light wavelengths. Being a newly developed drop sensor, PMWLDS shortens the length of the fiber sensor, makes an adjustable couple between liquid drop and fiber sensor, avoids the capacitor sensor's signature loss, etc. All the...

A new drop analysis method for liquid property study, called image drop analysis (IDA), with CCD, has been developed and its abilities to monitor the drop growth and to measure the drop volume by image acquisition and digital image processing technology are introduced. The remarkable advantage of IDA is that there is no need to determine the dielectric constant of the tested liquid and it can be used for measuring unknown liquids. Image drop analysis provides not only the volume, but also the shape information for the drop during its growth. By merging IDA and fiber drop analysis (FDA) into a fiber‐image drop analyzer (FIDA), a volume‐based fiber drop trace (VFDT) is obtained; it is independent of the speed of drop growth and the volatility of liquids. Graphic results are presented.