Noncontacting measurements

The noncontact measurement principle, usually called optical or radiation temperature measurement, is based on detecting electromagnetic radiation emitted from an object. In ventilation applications this method of measurement is used to determine surface temperatures in the infrared region. The advantage is that the measurement can be carried out from a distance, without contact with the surface, which possibly influences the heat balance and the temperatures. The disadvantages are that neither air (or other fluid) temperature nor internal temperature of a material can be measured. Also the temper-... 

The measurement range is dependent on the instrument but can cover the range -50 to +500 °C. The accuracy is not as high as the best contact thermometers. One reason for this is that the emissivity of the surface has an effect on the measurement result, and an emissivity correction is necessary for most instruments. The positive features are noncontact measurement and very fast dynamics, which enable a rapid scan of surface temperatures from a distance this is convenient when carrying out, for example, thermal comfort measurements. 

This aspect is not included here, but is related to optical flow diagnostics. It is based again on the principle of the optical Doppler effect. Multifunctional equipment is available for noncontact measurements of flow-induced vibration on surfaces of structural elements, for acoustic measurements, and for calibration of accelerometers and vibration transducers. 

Yamanaka, K. (1995). New approaches in acoustic microscopy for noncontact measurement and ultra high resolution. In Advances in acoustic microscopy, Vol. 1 (ed. G. A. D. Briggs), pp. 301-42. Plenum Press, New York. [226,292]... 

Holistic measurement of the entire workpiece obtaining dense volumetric data Fast inspection and reverse engineering of complex geometrical features Noncontact measurement, without probing and clamping stresses to the part Inspection of complex and internal features produced by additive manufacturing In-depth realistic visualization of the object s details... 

Obviously, ellipsometry is a noncontact measurement method. By applying windows, measurements can be carried out with the specimen in process or in a vacuum. 

Intermittent contact AFM is similar to the noncontact AFM mode except that the vibrating cantilever is brought closer to the sample so that at the maximum amplitude it makes slight contact with the surface (i.e., taps the surface). The intermittent contact region is shown on Fig. 2. As with noncontact measurement, the change in cantilever oscillation amplitude is in response to variation in tip-to-sample spacing. 

The two-dimensional quantitative approach has been in existence since the early 1930s when the need to better understand the manufacturing process necessitated the desire to characterize the surface. More recently, with the advances in computing and data storage, three-dimensional quantitative analysis has gained popularity. Three-dimensional measurement is more suited for noncontact measurement techniques due to the speed of data acquisition. 

Tissues such as skin have also been studied using photothermal methods, especially IR radiometry, which is capable of noncontact measurement, and is robust to alignment instabilities. In addition to the thermal and optical depth profiling of the various layers of the skin, photothermal spectroscopy has been used to study the time-dependent penetration of topically applied cosmetics and sunscreens below the skin surface. Photothermal studies have been used to monitor the time for which a topically applied film exists as a discrete phase on the outer surface of the skin. 

Dimensional Measurements. Many commercial laser interferometers are available for purchase and can be used for measurements of length, distance, and angle. Industries that require noncontact measurements of complex parts use laser interferometers to test whether a part is good or to maintain precise positioning of parts during febrication. Laser interferometers are widely used for these purposes in the automotive, semiconductor, machine tool, and medical- and scientific-parts industries. 

The acceleration at selected locations on the sample can also be measin-ed using a laser Doppler vibrometer (LDV) (187). The advantage of the LDV is that it is a noncontact measurement and does not disturb the vibration of the sample. Reference 187 describes a measurement setup that operates in the freqnency range 500-2500 Hz, temperature range 0-40°C, and at pressnres up to 500 psi. 

Liquid-level measurements are relatively straightforward, and the transducers fall into the categories of contactor noncontact. Measurements maybe continuous, in which the liquid level is monitored continuously throughout its operating range, or point, in which the liquid level is determined to be above or below some predetermined level. 

Figure 4.1.14. The Bruker Matrix-E, a Fourier transform near-infrared (FT-NIR) spectrometer (Bruker Optics Inc., 19 Fortune Drive, Manning Park, BiUerica, MA 01821-3991) (A) illustrating the noncontact measuring concept and (B) mounted for analyzing sugarcane pulp passing underneath.

Certain industrial monitoring requires more than a single noncontact measurement. In order to characterize paper, for example, up to three optical heads can be directed at one measurement point, measuring in parallel the transmission, the specular reflectance (gloss), and the diffuse reflectance... 

Sanchez, D. Johnson, N. Li, C. Novak, P. Rheinlaender, J. Zhang, Y. Anand, U. Anand, P. Gorelik, J. Frolenkov, G. I., Noncontact measurement of the local mechanical properties of living cells using pressure applied via a pipette. Biophysical Journal 2008, 95, 3017-3027. 

Optical caHper measurement Due to the deficiencies of the air bearing sensor and the need for a precise noncontacting caHper measurement, most sensor manufacturers currently push the development of optical noncontacting measurement methods. They consist of three sensors ... 

The experiments were performed at frequencies between 10 and 10 Hz using a test design that made it possible to measure the microwave absorption of the system to be measured in one beam by comparison with a parallel beam. The design chosen permitted noncontact measurement of both the electric and magnetic contributions to the total electromagnetic response. An effective medium analysis permits extraction of the metallic components from the total DF of the heterogeneous system. 

Although conventional methods of temperature measurement using thermometers and thermocouples are still commonly used for many applications, IR sensors have become less expensive, more reliable, and electrically interchangeable with conventional thermistors and thermocouples. For this reason, noncontact measure-... 

Qin, J. and Lu, R, (2006) Hyperspectral diffuse reflectance imaging for rapid, noncontact measurement of the optical properties of turbid materials, Appl... 

H. Kobatake, H. Fukuyama, 1. Minato, T. Tsukada, and S. Awaji, 2007, Noncontact measurement of thermal conductivity of liquid silicon in a static magnetic field , Appl. Phys. Lett. 90, 094102 1-3. 

PAS applications in chemical analysis have been widely reported, because of its unique features such as nondestructive, noncontact measurement, simple sample prepa-... 

The electrical conductivity of the i-stacked polymer was investigated by the flash-photolysis time-resolved microwave conductivity (FP-TRMC) method [57-68]. We could observe the charge mobility in 22e through the stacked r-electron systems in a single polymer chain using this noncontact measurement technique [30], Polymer 22e was dispersed in a polystyrene film without any dopants, and the cast film on quartz was excited by a laser pulse at 355 nm. The kinetic traces of microwave... 

Obtain dimensional data. Step 2 utilizes dimensional metrology equipment to obtain all the relevant dimensional data necessary to create a design drawing or CAD model of the part. The use of digitizing or scanning may be needed. The dimensions of the part can be measured by various instruments (a) noncontact measurement,... 

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