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Sensing for the Color of the Perfect Tomato
Published in Denise Wilson, Sensing the Perfect Tomato, 2019
The performance of color-sensing technologies depends largely on their design approach. Spectrophotometers are designed to measure color at very high resolution at a single point. Thus, their accuracy and color resolution are high while their spatial resolution remains low. Colorimeters and color sensors behave essentially as spectrophotometers, measuring color at a single point, albeit at much lower color (wavelength) resolution. Cameras, on the other hand, are designed to measure images, capturing color at high spatial resolutions but limited wavelength resolutions (red, green, blue). Hyperspectral and multispectral imagers combine qualities of both cameras and spectrophotometers, providing high color resolution at spatial resolutions that far exceed conventional spectrophotometers. And, finally, fluorometers are specialized instruments designed to measure light emitted from fluorophores like chlorophyll that are found naturally inside plants and fruits. For monitoring color in tomatoes, where a fluorometer would rely on natural fluorophores, accuracy and resolution can be quite low because the fluorescence signal involved is small and subject to interference. Outside of a highly controlled environment, fluorometers can have a wide range of performance issues. And, fluorometers as well as spectrophotometers will, in many cases, require glass optical fibers to attain maximum accuracy. This limits their durability, as glass cracks easily, particularly in field use situations.
Molecular Fluorescence and Phosphorescence
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Ricardo Q. Aucelio, Sarzamin Khan, Andrea R. da Silva, Fernando M. Lanças, Emanuel Carrilho
Instruments in which wavelength selection is accomplished with filters (band filters or even high pass or low pass filters) are referred to as fluorometers. They are designed to perform detection at fixed wavelength band pass (selected by filters) in a very simple unit composed of a radiation source, filters (at least the one to select the wavelength of emission), sample compartments, a monochannel PMT-type detector, and simple output devices, as they are designed to be inexpensive and easy to operate. In ratiometric fluorometers, the ratio of the sample signal to a reference signal is used to compensate instrumental fluctuations. In double-beam filter fluorometers, the excitation radiation is divided in two (in an alternated way by means of a modulation disk chopper): one to excite the sample and another to serve as reference detected in a specific detector. Fluorometers are suitable for quantitative applications when neither spectral scanning nor high resolution is required. Filters allow a more intense transmission of radiation to reach the sample, thus improving detection limits.
Measurement and Analysis of Flow
Published in James L. Martin, Steven C. McCutcheon, Robert W. Schottman, Hydrodynamics and Transport for Water Quality Modeling, 2018
James L. Martin, Steven C. McCutcheon, Robert W. Schottman
A filter fluorometer is a spectometer that measures the relative intensity of light emitted by a fluorescent substance. A fluorometer consists of a light source, a primary filter, sample holder, secondary filter, sensing device, and a readout device (Figure 21). The light source will vary depending on the characteristics of the dye to be measured, as discussed below. Light from the source passes through a primary filter that limits the light reaching the sample to a narrow band centered about the wavelength of maximum excitation for the dye. For measurements, the filtered light is directed through a sample in a holder of known volume and optical properties. The light emitted from the sample passes through a secondary filter that limits the light reaching the photomultiplier to a narrow range fluoresced by the dye. A photomultiplier detects the incident radiation and produces an electronic signal. The signal intensity is converted to a readout to indicate the amount of dye present in the sample. The types of filters, sources, and photomultipliers vary with the instrument and dye used. Manufacturers' specifications, Wilson (1968), and McCutcheon (1989) are the best sources of information for the appropriate filters.
Influence of chlorophyll a quantification methods in ecological quality indices
Published in Inland Waters, 2019
Xavier Sòria-Perpinyà, Vicente Sancho-Tello, María José Rodriguez, Concha Durán, Juan Miguel Soria, Eduardo Vicente
Currently, the most widely used devices are field fluorometers, which produce real-time, continuous information, thus facilitating the collection of vertical profiles of chlorophyll with little effort, using minimum processing to obtain as much information as possible on profiles of interest. These fluorometers operate by means of LEDs that emit at specific wavelengths and excite the sample while a detector measures energy in response to excitation. The drawback is that the optical properties of phytoplankton depend on the size, shape, pigmentation, taxonomic composition, photoadaptation, and physiological status. For example, exposure to saturating light will immediately cause a fluorescence depression, but any change in the concentration of Chl-a happens much slower (over hours; Kiefer 1973, Cullen et al. 1988). Users must be aware of some general problems associated with the in situ and in vivo fluorescence measurements, such as effect of irradiance, lack of dark adaptation, and effects of nutrient limitation (Gregor et al. 2005). Therefore, the direct comparison of the fluorescence yield to other parameters of the phytoplankton biomass can be problematic (Falkowski and Kiefer 1985) because it might be contaminated by other fluorescent sources such as detrital pigments (Marra and Langdon 1993) and colored dissolved organic matter (Proctor and Roesler 2010, Röttgers and Koch 2012).
Review of the state-of-the-art for monitoring urban drainage water quality using rhodamine WT dye as a tracer
Published in ISH Journal of Hydraulic Engineering, 2023
Kuldeep Swarnkar, Vinay Nikam, Kapil Gupta, Jonathan M. Pearson
The use of fluorescent dyes as tracers was also described by Fyffe (2013). They explained the quantity of dye required, types of dye, and use of calibration to conduct tracer studies. The advantage of fluorescent tracing dyes (such as rhodamine WT) is that they emit a significant amount of absorbed energy and may be detected at extremely low concentrations. It was shown that the operation of a fluorometer may be affected by temperature, pH, sediment concentration, and NaCl concentration. So, the onsite calibration of the fluorometer has been important for ensuring that the temperature (the main significant factor) of the water resembles the onsite condition.