INSTRUMENTATION

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INSTRUMENTATION A servo development apparatus of great flexibility and variety is described and illustrated, with a discussion of some useful components and accessories by

ΤΉΟΜ time to time it has been possible to describe in this column an instrument that has direct and useful analyti­ cal application. Experience has shown that mention or de­ scription of it is welcomed even if it has been advertised or described elsewhere. If the analytical use is immediate and self-evident, it is more than likely that the theory and funda­ mental principles have been known for many years. There is rarely any lack of competent and progressive chemists to apply a new instrument to specific analytical problems, but curiously enough, the process continues to be called instru­ mentation or instrumental analysis long after it has passed into the hands of button-pushing technicians.

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Analytical Research We have long insisted that research in analytical instru­ mentation of the "useless" variety is urgently needed and that its proper place is in the university. Not that this will be con­ ceded in academic surroundings, because there one hears the constant complaint that there are already so many instru­ ments that it is not possible to tell the students about them. This attitude cannot halt the march of progress, but it helps immeasurably. Even where research is being attempted, the approach seems to be from the specific to the general, to illus­ trate and work with all the instruments which the budget will allow and shrug helplessly for that which must be left undone.

Figure 1

Ralph

H.

Müller

The industrial attitude is similar in emphasizing the specific rather than the general. One can name his own price if he guarantees the instrumental solution of a specific headache. We know the answer to the alternative suggestion—but we still keep trying! For those who believe that the best in­ terests of science are served by patient data gathering we acid parenthetically that an automatically recording instrument is the data-gatherer par excellance. Murphy's recent editorial plea for the support of analytical research will undoubtedly elicit the response that it deserves, but as long as even modern analysis continues to be regarded as an insurance policy for the protection of more vital enter­ prises, one cannot hope for any extravagance in the more ex­ citing and visionary pursuits of the analyst. Servomechanisms We reiterate this biased preference for that portion of the instrument which is usually hidden in a black box, by describ­ ing some very useful components and accessories that will interest many of our readers. An increasing number of analy­ tical instruments are being developed or redesigned to take advantage of the servomechanism principle. As stated by Hazen, "A servomechanism is a power-amplifying device in which the amplifying element driving the output is activated by the difference between the input and the output." Within such systems one may require potentiometers, selsyns, rotatable transformers, driving motors, and intermediate gear trains. The electronics expert can usually assemble a com­ plex circuit on a homemade or commercial "breadboard" in a short time and rapidly confirm or modify his original circuit specifications. I t has always been difficult, time-consuming, and expensive to set up an experimental mechanical system of comparable precision and reliability. Among many services in the entire field, Servomechanisms, Inc., 142 Mineola Blvd., Mineola, Ν. Υ., has made available a servo development apparatus of great flexibility and variety. As shown in Figure 1, an aluminum foundation plate 8 X 8 X 3 /s inch full of 3/Ί6 inch holes spaced 1/4 inch apart can be mounted on legs to support it above a table, to separate it from similar plates, or to mount a plate at right angles. Pre­ cision-machined blocks for holding accessories and bearing blocks to hold shafts in ball bearings can be bolted to the base plate in any desired location. A wide range of parts is avail­ able, including stainless steel centerless ground s / 1 6 inch shaft­ ing in various lengths, box collets used to avoid shaft axial drift, and a wide assortment of stainless steel gears. The mechanical portion of an entire servo system so shown can be set up in a few minutes and is readily dismounted for another problem. Some of the details are more evident in Figure 2. All mounting blocks are provided with 8-32 nuts captured in a T slot and 8-32 screws are used from beneath the foundation 21 A

ANALYTICAL

22 A

plate to secure the blocks. These screws are provided with large knurled heads for finger-tight adjustment. For more permanent setups Allen cap screws are recommended. All blocks are dimensioned to hold motors, etc., exactly 1.5 inches off base. The blocks are precision-bored to accept the flange mounting of standard commercial units such as Kearfott motors, Bendix Autosyn, Fairchild potentiometers, etc. The gear clamps are ingeniously devised to eliminate the errors of the usual shaft set screw. An example is seen between the end of the motor shaft and the mounting block. A small tapered and slit collet fits into a tapered recess in the gear. A large cap screw threads onto the hub of the gear and as this is drawn up (finger-tight) the collet is shrunk tightly and concentrically to the shaft.

Kleet . . . .

Photometers Kleet

CHEMISTRY

Summerson Photoelectric Glass Cell

Colorimeter No. 900-3

The Klett Flourimeter

No. 2070

Figure 2

Designed for the rapid and accurate d e t e r m i n a t i o n of thiamin, riboflavin, and other substances which fluoresce in solution. The sensitivity and sta­ bility are such t h a t it has been found particu­ larly useful in determining very small a m o u n t s of these substances.

Servomechanisms, Inc., furnishes a complete kit containing a liberal assortment of these components and additional items can be ordered from an extensive stock. The company is also prepared to supply packaged servo units and laboratory servo testing apparatus and is engaged in development work in this field. Information regarding these products can be obtained from the Control Systems Company, G.P.O. Box 334, New York, Ν . Υ. We have often attempted the solution of an instrument problem by wholly electronic means, even where it was evident that an intermediate mechanical element would be preferable. No doubt many other's have done the same in an effort to avoid the delay and expense required by precise machine work. The servo development apparatus should be very useful in the research laboratory for this and many other problems.

KLETT SCIENTIFIC PRODUCTS

Book on Electronic Instruments ~We have made frequent reference to the Μ.Ι.Τ. Radiation Laboratory Series of monographs published by McGraw-Hill. These are appearing now in rapid succession and we wish to record our particular enthusiasm for Volume 21, on electronic instruments, by Greenwood, Holdam, and-Macrae. More than 700 pages deal with five general topics: Part I, Elec­ tronic Analog Computers; Part I I , Instrument Servomecha­ nisms; Part I I I , Voltage and Current Regulators; Part IV, Pulse Test Equipment; Part V, Design and Construction of Electronic Apparatus. With the possible exception of Part IV, there is hardly a page in this stimulating and authoritative work which does not hold some promise and utility for solving the instrument problems of the analyst.

ELECTROPHORESIS APPARATUS · BIO-COLORIMETERS G L A S S ABSORPTION CELLS · COLORIMETER NEPHELOMETERS · G L A S S STANDARDS · KLETT REAGENTS

Klett

Manufacturing

Co.

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