Photo-cell detector

Rubidium oscillators ate the lowest priced members of the atomic oscillator family. They operate at 6,834,682,608 Hz, the resonance frequency of the mbid-ium atom ( Rb), and use the rubidium frequency to control the frequency of a quartz oscillator. A microwave signal derived from the ciystal oscillator is applied to the Rb vapor within a cell, forcing the atoms into a particn-lar energy state. An optical beam is then pnmped into the cell and is absorbed by the atoms as it forces them into a separate energy state. A photo cell detector measnres how much of the beam is absorbed and times a quartz oscillator to a frequency that maximizes the amount of light absorption. The qnartz oscillator is then locked to the resonance freqnency of rabidinm, and standard frequencies are derived and provided as outputs (Fig. 8). 

The photo cell senses light of all wavelengths that is generated by fluorescence but the wavelength of the excitation light can only be changed by use of an alternative lamp. This simple type of fluorescence detector was the first to be developed, is relatively inexpensive, and for certain compounds can be extremely sensitive. Typical specifications for a fluorescence detector are as follows ... 

A diagram of their detector is shown in figure 21. The UV adsorption system consists of a low pressure mercury lamp emitting light at 254 nm and a solid state photo cell with quartz windows allowing the photo cell to respond to light in the UV region. 

In the laboratories of BASF (Badische Anilin- and Soda-Fabrik) at Ludwigshafen, the importance of infrared spectroscopy for industrial purposes was realized as early as the 1930 s. The first IR instrument with a modulated beam was built by Lehrer in 1937 and modified to a double beam instrument with optical compensation in 1942. Luft described the first non-dispersive infrared analyzer in 1943. He used the gas to be analyzed as absorber in a photo-acoustic detector cell. Thus, the instrument was sensitive only to this gas. He also provided a survey of early industrial applications of infrared spectroscopy (Luft, 1947). 

It is seen that the ultimate resolving power of the diode array detector will depend on the semiconductor manufacturer and on how narrow the individual photo cells can be commercially fabricated. 

An example of the use of a simple fluorescence detector is afforded by the separation of the mixture of priority pollutants shown in figure 2. The separation was actually monitored by the fluorescence sensor of the TriDet detector the design of which will be discussed later. The excitation light was approximately monochromatic at 254 nm and all the fluorescent light was focused on the photo cell. It is seen that an excellent sensitivity is obtained. 

Fig. 46. Optical diagram of the Polytec MIR 160 Fourier spectrometer (No. 5b in Tables 2, 3, 4). M 1, M 2, M 5, M 6, M 7 plane mirrors M 3, M 4 paraboloid mirrors MS spherical mirror MT toroid mirrors G Globar source S high pressure Hg-lamp L He-Ne-laser IS Interferometer scanner BS beampslitter PC photo-cell D pyroelectric detector WL white light source...

A diagram of the optical system of the Perkin-Elmer LC 95 dispersive, variable wavelength detector is shown in Figure 7. Light from a UV source, a deuterium lamp, falls onto a concave mirror that collimates the beam onto a diffraction grating. The dispersed beam is then focussed by means of another concave mirror, through an aperture in a plane mirror, onto another plane mirror, through the sample cell and then onto a photo cell. 

A few methods can be used to detect your adhesive on the parts. One standard method is to incorporate a fluorescent agent into the adhesive and use a fluorescence detector to monitor its presence. Photo cells or a camera system can also be effective. If you use a three-dimensional camera system, you can measure the width, height and position of the bead of adhesive. 

Photo- decomposition High intensity sources may cause sample decomposition, which depends on the residence time of the sa le in the detector cell. 

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