Photoelectric beam device

Photoelectric Beam Another type of presencesensing device uses light beams and photoelectric sensors (Figure 13-12). An array of beams forms a horizontal, vertical, or combined pattern. If someone inserts something into the array and it interrupts one or more of the beams, the machine stops or will not operate. Because the array is not easily seen, one must depend on a display to know if it is functioning correctly. 

Other Transducers. Ultrasound also has been used for the measurement of force, vibration, acceleration, interface location, position changes, differentiation between the composition of differing materials, grain size in metals, and evaluation of stress and strain and elasticity in materials. Sonic devices can used to detect gas leaks, and to count discrete parts by means of an interrupted sound beam. Frequently, an ultrasonic device can be applied where photoelectric derices are used. Particularly tn situations where light-sensitive materials are being processed (hence presence of light must be avoided), ultrasonic devices may be the detectors of choice. 

Tyndall Meter—The Tyndall meter is a device developed by Tolman and Vliet (1919) for measuring the intensity of a Tyndall beam. The apparatus is shown in Figure 54 and consists of a central cell which contains the suspension to be measured. This is illuminated by a light beam whose intensity has been standardized. This beam of light passes through the cell. The intensity of the resulting Tyndall beam in the cell is measured by means of a photoelectric meter, or an illuminometer. Several variations of the Tyndall meter are possible, as follows ... 

We have seen that the shape and size of the unit cell of a crystalline substance may be determined from the positions of the reflected beams. The number of atoms in the cell follows directly from, the size of the cell and the density of the substance for information concerning the positions of atoms, however, it is necessary to rely almost entirely on the relative intensities of the beams. There are a number of photoelectric devices known for measuring the degree of blackness on a clear film or the degree of whiteness on a black film a good measurement of the intensity of beams is obtained by using a movable Geiger counter instead of a film, for the intensity of ionization within the spectrometer chamber is proportional to the number of photons received. Reflections from some planes may be completely absent. 

In its simplest form, colorimetry consists of visual matching of the color of the sample with that of a series of standards. A colored compound is first formed by suitably reacting the constituent to be determined, then the colored solutions are racked side-by-side in Nessler tubes for viewing from the top. The approximate concentration of the unknown is estimated by finding which standard most closely matches the unknown in color. Visual colorimetry suffers from poor precision since the eye is not as sensitive to small differences in absorbance as is a photoelectric device. The use of a Duboscq colorimeter constitutes a more refined method of analysis for color comparison. This is equipped with an eyepiece with a split field that permits the ready comparison of beams passing through sample and standard. 

Tetracyanoquinodimethane (TCNQ) and related compounds [10], have been extensively investigated in the last decades. When combined with tetrathiafulvalene (TTF) and some metals such as Ag and Cu, it may show very useful properties such as electrical and optical bistability. However, to apply these organic thin films in electronic or photoelectric devices, it is of great importance that the films should exhibit few impurities and defects and it is also desired that the films crystallinity can be controlled. For these reasons, we explore an ionized cluster beam deposition method to fabricate organic crystalline thin films. 

The radicfrequency (capacitance) presence-sensing device uses a radio beam as part of the machine control circuit. When the capacitance field is broken, the machine stops or will not activate. Like the photoelectric device, this device is only to be used on machines that can be stopped before the worker can reach the danger area. This requires the machine to have a friction clutch or other reliable means for stopping. This device allows freer movement for the operator but does not protect against mechanical failure. In addition, antennae sensitivity must be properly adjusted this adjustment must be maintained properly. 

Spectrometric methods are a large group of analytical methods that arc based on atomic and molecular spectroscopy. Spectroscopy is a general term for the science that deals with the interactions of various types of radiation with matter. Historically, the interactions of interest were between electromagnetic radiation and matter, but now spectroscopy has been broadened to include interactions between matter and other forms of energy. Examples include acoustic waves and beams of particles such as ions and electrons. Spectrometry and spectrometric methods refer to the measurement of the intensity of radiation with a photoelectric transducer or other type of electronic device. 

Photosensors. These are the most commonly used sensing and scanning devices. A photoelectric control consists of a light source, photoreceiver, amplifier, and output. A beam of light from the hght source activates the photosensitive elements of the photoreceiver which produces an electric signal, which drives a relay to activate the diverting mechanism. When used as a sensor, photoelectric controls can be used to ... 

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