Optical measurements instrumentation

Optical Measuring Instruments. Their Construction, Theory, and Use. By L. C. Martin, F.R.A.S., D.Sc., A.R.C.S., D.I.C., Lecturer in the Optical Engineering Department, Imperial College of Science and Technology, South Kensington. With 172 figures. 17s. 6d. net. 

Because light emitted from inductively coupled plasma torches is characteristic of the elements present, the torches were originally introduced for instruments that optically measured the frequencies and intensities of the emitted light and used them, rather than ions, to estimate the amounts and types of elements present (inductively coupled plasma atomic emission spectroscopy. 

Optical measurements permit the quantification of visibility degradation under different conditions. Several instruments are capable of measuring visual air quality, e.g., cameras, photometers, telephotometers, transmis-someters, and scattering instruments. 

An ICP-OES instrument consists of a sample introduction system, a plasma torch, a plasma power supply and impedance matcher, and an optical measurement system (Figure 1). The sample must be introduced into the plasma in a form that can be effectively vaporized and atomized (small droplets of solution, small particles of solid or vapor). The plasma torch confines the plasma to a diameter of about 18 mm. Atoms and ions produced in the plasma are excited and emit light. The intensity of light emitted at wavelengths characteristic of the particular elements of interest is measured and related to the concentration of each element via calibration curves. 

Optical particle counter An optical-electronic instrument for measuring the numbei" of airborne particles in different size ranges. 

Independent arrays of telescopes have been discussed for decades but have generally not been successful, except for radio telescopes, where interferometry is a key virtue, aided by the fact that the individual telescope signals can be amplihed and combined while preserving phase information. This is not practical in the optical, thus there are significant inefficiencies in sensitivity by coherently combining the light from an array of optical telescopes. Instrumentation for an array of telescopes has also been a cause of difficulty. Perhaps the best known successful array has been the VLT with four 8-m telescopes, each with its own suite of science instruments, and the capacity to combine all telescopes together for Interferometric measurements. 

However, these analogues are actually hypothetical. The reason for this is that it is nearly impossible to obtain optical measurement components, such as the source and the detector, whose response to light across the visible spectrum is flat (or nearly so). However, this is not an impossible task and we find that an excellent match can be obtained to the transmission functions of 7.8.21., i.e.-those of the Standard Observer. This is typical for commercially available instruments. Now, we have an instrument, called a Colorimeter, capable of measuring reflective color. 

Based on these capabilities, the RRS detection method has already found commercial application in the nutritional supplement industry (BioPhotonic Scanner , Pharmanex LLC, Provo, and Utah), which has placed thousands of portable instruments with their customers for rapid optical measurements of dermal carotenoid levels, and which has further developed the instrumentation for rugged field use (Bergeson et al. 2008). 

One other, very descriptive classification of flow-through sensors is based on the location of the active microzone and its relationship to the detector. Thus, the microzone can be connected (Figs 2.6. A and 2.6.B) or integrated (Fig. 2.6.C) with the measuring instrument. Sensors of the former type use optical or electric connections and are in fact probe sensors incorporated into flow-cells of continuous analytical systems they can be of two types depending on whether the active microzone is located at the probe end (e.g. see [17]) or is built into the flow-cell (e.g. see [18]) — in this latter case. 

The BioView sensor (DELTA Light Optics, Denmark) was developed especially for industrial applications. It is capable of completely automatic optical measurement for monitoring and control of different bioprocesses. The instrument is conceived to withstand harsh industrial environments (e.g., high temperature, moisture) and electromagnetic interference. For data transfer a single-fiber asynchronous modem is used, which allows a distance between the computer and spectrometer of up to several hundred meters. 

Figure 2.20 The sensor signal from two MISiC-FET sensors (upper curves) and the optical reference instrument (lower curve) during engine test rig measurements to simulate standard drive, (from [52]. 2004 IEEE. Reprinted with permission.)...

Substances that can rotate the orientation of plane-polarized light are said to have optical activity. Measurement of this change in polarization orientation is called polarimetry, and the measuring instrument is called a polarimeter. 

Fig. 1 Chemical interaction mechanisms, basic components of the optical sensor instrumentation and their operation. Mechanisms direct measurement of chemical compounds that exhibit spectroscopic properties (1 A) and measurement of light originating from a chemical or a biological reaction in chemiluminescent or bioluminescent phenomena (IB) 2 optodes based on the interaction of indicators and labels with light, which are immobilized in a support and sensors that modify the intrinsic physical or chemical properties of a waveguide (refractive index, phase, etc.) as a result of the presence of the analyte (3A), a recognition element (35), an intermediate analyte (3C) or an indicator (3D)...

The success of an optical measurement will be controlled by the quality of the optical components that make up the instrument, and the accuracy of their alignment. For this reason, Chapter 9 is devoted to the selection of specific components to accomplish a required task. Since such a decision is influenced by the construction of an element, the underlying physics and design criteria used in the manufacture of optical components are presented. This discussion is combined with alignment protocols that the author and his students have found useful in their own laboratory. 

An imaging measuring instrument for the optical analysis of roughness (MicroGlider, Germany) was used as a complementary method because of its large-scale verti-... 

Power measurements require the measurement of the torque and the rotational speed. The torque can be measured using a torsion shaft with strain gauges, electrically with eddy-current torque transducers, or mechanically with a swiveling motor. The speed of rotation can be measured using mechanical, electrical (photocell), or optical (stroboscope) instruments. 

Turbidity reflects the amount of suspended matter in water (e.g., clay, silt, organic and inorganic matter, and plankton). The standard measure of turbidity is the turbidity unity (TU), which is based on the optical property of a water sample, causing transmitted light to be limited. As the number of particles increases, turbidity increases. The measuring instrument is called a nephelometer, and the readings are expressed as nephelometric turbidity units (NTU). 

---