Instruments, measuring micrometer

Fein-messen, n. precision measurement, -mes-ser, m. micrometer vernier, -messgerat, n. precision measuring instrument, -messlehre, /. micrometer caliper or gage, -mess-... 

In the contacting measurement techniques, the micrometer caliper is a common instrument. The micrometer, however, can only be used for pot measurements and this is done manually. A spring-loaded dial gauge can be moved over the extrudate if the thickness variations are small. Thus, the dial gauge can be used to monitor the variation of thickness with time, i. e., in the extrusion direction. If an accurate traversing mechanism is constructed, the dial gauge can also measure the thickness variation perpendicular to the extrusion direction. At the point of measurement, the opposite side of the extrudate has to be firmly supported to avoid measurement errors. 

Basically, the optical method uses equipment such as alignment telescopes, jig transits, and sight levels. Instruments with built-in optical micrometers for measuring displacements from a referenced line of sight enable an accurate determination of target movements, which are mounted on the machine. 

The nanometer- to micrometer-scale dimensions of supramolecular assemblies present many challenges to rigorous compositional and structural characterization. Development of adequate structure-property relationships for these complex hierarchical systems will require improved measurement methods and techniques. The following areas constitute critical thrusts in instrument development. 

Infrared (IR) spectroscopy, especially when measured by means of the Fourier transform method (FTIR), is another powerful technique for the physical characterization of pharmaceutical solids [17]. In the IR method, the vibrational modes of a molecule are used to deduce structural information. When studied in the solid, these same vibrations normally are affected by the nature of the structural details of the analyte, thus yielding information useful to the formulation scientist. The FTIR spectra are often used to evaluate the type of polymorphism existing in a drug substance, and they can be very useful in studies of the water contained within a hydrate species. With modem instrumentation, it is straightforward to obtain FTIR spectra of micrometer-sized particles through the use of a microscope fitted with suitable optics. 

Micrometer - An instrument by which highly accurate minute measurements of length, depth, or thickness may be made. 

Chemical Composition Aerosol composition measurements have most frequently been made with little or no size resolution, most often by analysis of filter samples of the aggregate aerosol. Sample fractionation into coarse and fine fractions is achieved with a variety of dichotomous samplers. These instruments spread the collected sample over a relatively large area on a filter that can be analyzed directly or after extraction Time resolution is determined by the sample flow rate and the detection limits of the analytical techniques, but sampling times less than 1 h are rarely used even when the analytical techniques would permit them. These longer times are the result of experiment design rather than feasibility. Measurements of the distribution of chemical composition with respect to particle size have, until recently, been limited to particles larger than a few tenths of a micrometer in diameter and relatively low time resolution. One of the primary tools for composition-size distribution measurements is the cascade impactor. 

The infrared spectrophotometer is the principal instrument used by scientists for ihcse measurements. Most laboratory spectrophotometers are of a dispersive design, i.e.. a prism or grating is used to separate the spectral components in the source radiation. Modern infrared spectrophotometers base it wide wavelength range from 2 to 50 micrometers. They lind use in research, quality control, and analytical service laboratories. 

There is no inherent sample size restriction, large or small, but is fixed by the optical components used in the instrument. The diffraction limit of light, roughly a few cubic micrometers depending on the numerical aperture of the optics used and the laser s wavelength, sets the lower bound.7 In a process application, the type of fiber optics used also affects sample volume examined. Macroscopic to microscopic samples can be measured with the appropriate selections of laser wavelength, laser power, and optics. 

Standard Reference Material 1470 is a 23 micrometer thick polyester film whose gas transmission characteristics with respect to helium, carbon dioxide, oxygen, and nitrogen have been carefully measured. A completely computerized manometric permeation measuring facility developed at NBS was used for the measurements. The steps taken to characterize the gas transmission rate of this material over the range of pressures from 67.5 kPa to 135 kPa and over the range of temperatures from 18 °C to 31 °C are described. The results obtained in these measurements are compared with those in the literature. The role of Standard Reference Material 1470 in improving the repeatability and reproducibility of gas transmission measurements employing other instrumentation is discussed. 

Particle Size Analysis. Particle size distribution measurements of the dry resin were made using a Micromeritics Sedigraph 5000D particle size analyzer. This instrument employs a gravity settling technique and uses Stokes law to determine the particle size. The PSD was run over the size range of 0.36 to 100 micrometers. All measurements were made in dibutyl sebacate as the suspending medium. 

The very hard materials can be checked using the standard pressure settings. For softer materials, this will cause undue distortions. The micrometer or vernier calipers need to be gently passed over the item. The faces of the instrument must just touch the surface. This can be felt through the instrument as a very mild resistance. The measurements will represent the high points on the surface. 

Apparatus. The diameters of gel disks were measured with a Cambridge Instruments Stereoscope with a micrometer reticle. An Ohaus GA200D balance was used to weigh swollen gel disks. The volume was calculated from the weight assuming a density of 1.00. An Orion Research pH meter (Model EA920) and electrode were used to monitor pH. A BioRad electrophoresis chamber was used to form the gel slab. 

Aside from meter sticks, there are other instruments used for linear measurement such as the caliper and micrometer. Their designs and mechanisms for use are very different, but both meet specific needs and have specific capabilities. 

---