The Transmission Type Probes

FIGURE 4-4 Industrial optic fiber probe for cell concentration measurement. 

FIGURE 4-5 Measured cell concentration in industrial glutamic acid fermentation. 

FIGURE 4-6 Representative configurations of reflection type optic fiber probes (Krohn, 1986). 

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Figure 11.17 Temperature probes for contact measurement, (a) The reflection-type probe, (b) the transmission-type probe.

Both the transmission-type probe and the reflection-type probe, need be calibrated for their measuring range in local solids concentration. The calibration of optic fiber probes is known to be a difficult problem. Calibration methods fall into two categories the first is to calibrate a probe against agitated or fluidized liquid—solid systems the second is to use particle free-fall in gas—solid systems or the traditional pressure drop method for fluidized solids the third is in a flow system with particle density deduced from mass flux of particles and measurement where phase velocities were nearly equal. 

Since dispersion of solids in a fluid-particle system is in a random state of movement, and the signals of light output from both the transmission-type and the reflection-type probes are dependent on diameter, morphology, chromaticness, distance and refractivity of the particles, the signals produced by particles in random movement can only be described by random data analysis. 

There are three types of electron microscopes commonly used for microanalysis. These are the scanning electron microscope (SEM) with X-ray detectors, the electron probe microanalyser (EPMA), which is essentially a purpose built analytical microscope of the SEM type, and transmission microscopes (TEM and STEM) fitted with X-ray detectors. In a TEM, compositional information may also be obtained by... 

Figure 21.4 Nonlinear transmission for the internal type [70, 77] samples Ag(0) i when probed at 532 nm.

The atom-probe field ion microscope is a device which combines an FIM, a probe-hole, and a mass spectrometer of single ion detection sensitivity. With this device, not only can the atomic structure of a surface be imaged with the same atomic resolution as with an FIM, but the chemical species of surface atoms of one s choice, chosen from the field ion image and the probe-hole, can also be identified one by one by mass spectrometry. In principle, any type of mass analyzer can be used as long as the overall detection efficiency of the mass analyzer, which includes the detection efficiency of the ion detector used and the transmission coefficient of the system, has to be close to unity. 

This type of electron microscope is completely different in principle and application from the conventional transmission-type electron microscope. In the scanning instrument, the surface of a solid sample is bombarded with a fine probe of electrons, generally less than 100 A in diameter. The sample emits secondary electrons that are generated by the action of the primary beam. These secondary electrons are collected and amplified by the instrument. Since the beam strikes only one point on the sample at a lime, the beam must be scanned over the sample surface in a raster pattern to generate a picture of the surface sample. The picture is displayed on a cathode ray tube from which it can be photographed. 

UV-Vis process analysers can be used in a noncontact mode as the source radiation can be passed though a window in a process pipe, for example, and the emitted radiation detected on the other side of the pipe. This means that the sample can be subjected to a measurement without its flow being impeded or its composition changed in any way. Optical fibres are used to transmit the radiation to and from the sample, which can be in a distant location, a hazardous area or in a harsh environment such as a high temperature reaction vessel. The most common forms of optical fibre probes used for UV-Vis measurements are of the transmission and ATR types (Figure 9.12). The petroleum and chemical industries use UV-Vis spectroscopy for monitoring many of their processes ... 

Hartge et al. (1988) developed a optic fiber probe of the minimum size for velocity and concentration measurements. This kind of probe which allows the transmission of incident and reflected lights in a single fiber, as already shown in Figure 4-9, falls into Type C in Figure 4-24. The authors detailed their measuring method and experimental results, and pointed out... 

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