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FrequencyLinear Drive for Spectrographic RecorderW. E. Deeds Citation: Review of Scientific Instruments 27, 543 (1956); doi: 10.1063/1.1715629 View online: http://dx.doi.org/10.1063/1.1715629 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/27/7?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Low-Frequency Circuit for Driving a Galvanometer in Forced Linear Oscillation Am. J. Phys. 33, 468 (1965); 10.1119/1.1971698 An Apparatus for Recording Pressure on a Spectrographic Plate Rev. Sci. Instrum. 17, 213 (1946); 10.1063/1.1770469 A Recording Spectrograph for the Far InfraRed Rev. Sci. Instrum. 9, 404 (1938); 10.1063/1.1752377 A High Sensitivity Mass Spectrograph with an Automatic Recorder Rev. Sci. Instrum. 8, 51 (1937); 10.1063/1.1752235 A Recording Infrared Quartz Spectrograph Rev. Sci. Instrum. 4, 123 (1933); 10.1063/1.1749086
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NOTES 543
TABLE 1. Experimental values for needle diameter, lengths of needle and gUIde tube, and the rotation speed for needles 20 ~ 1 00 1',
Length Needle of Rotation
Diameter Length guide tube speed ------------
I' mm mm rpm 20 0.8 0.4 60 30 1.2 0.6 60 40 1.6 0.8 60 50 2.0 1.0 90 60 2.4 1.2 90 70 2.8 1.4 90 80 3.2 1.6 120 90 3.6 1.8 120
100 4.0 2.0 120
bearing, H the screw for adjusting pressure of S, S the spring to load the needle, I the screw for adjusting the location of the needle, and .T the work.
The needle A doing the boring is fixed by the sleeve B and is moved up and down without rotating in the cylinder C, and also is always pressed against the surface of the work by the spring S. The guide tube D is fitted at the top of the needle head. The function of D is to prevent the needle from bending or breaking due to pressure occurring with boring, and also to bore straight without eccentric motion. The long guide hole in D was made by drawing a minute metallic tube.
With the rotation of the needle in the guide tube, the needle often breaks as a result of excessive friction or the guide tube becomes worn, and therefore, it is desirable to hold the needle in the guide tube as far as possible without rotation. The spring Splays the role of loading the needle and also cushioning it to prevent breakage if it receives a shock.
The screw I is first rotated to the right drawing the needle into the guide tube. Next, the table is moved upward and the guide tube approaches the surface of the work. With rotation of the screw to the left after determining the position of the hole for boring, S pushes A out of the guide tube. Then, one drop of polishing and shaving oil is supplied to the needle and the boring is started by slow rotation of the needle as soon as the needle comes in contact with the surface of the work. To observe the position and the state of boring, an optical microscope was used. A mixture of petroleum, colza oil, and powder of agate (grain size 0.5~2 p.) was also used as polishing and shaving oiL
Table I shows the experimental values for the lengths of the needle and of the guide tube, the speed of rotation, etc., for needles 20~100 p. in diameter. In this experiment quenched carbon steel was used as the needle. The length of the needle should be 40 times its diameter. This length is capable of resisting the pressure added in the guide tube. Attention is paid to keeping half the length of the needle always in the guide tube. The gap between the needle and the guide tube should be as small as possible. The pressure on the needle should be 7~8 mg/p.2. When the pressure is greater than this, the needle is likely to break. Accordingly, in the cases of holes of 20 p. and 30 p., the pressure to be added to the needle was adjusted to the desired pressure by using the spring S' shown in Fig. 1. In contrast to the ordinary case, slower rotation of the main axis is desirable with the smaller needle diameters. In such a case, boring efficiency is lowered, but the needle is less likely to break and an excellent hole can be obtained. The present ap-
A B c D
FIG. 2. The holes ob,tained by this method. (A) 1> ~75 Jlo. /=1501'. (B) 1> =40 Jlo, t =100 Jlo. (C).1> ~25 Jlo. t ~100 1', and (D) 1> =20 p.. / =60 p.. X140.
paratus has a limit in that the greatest depth it can bore is about 5 times the diameter of the hole. In boring a deeper hole, the needle often breaks or twists off. The hole bored has an eccentric error of 1",2 1t,and is tapered by about 5",6 It when it is 75 It in diameter and 200 It in depth. Accordingly, to obtain a straight hole the error should be reduced to about 1~1.5 p. by passing a new needle through the hole once more. A burr often appears on the surface at the entrance and the exit of the needle. To prevent this, three s~eets are used and a specimen sheet is placed at the middle positIOn between them. After boring, the specimen sheet can be obtained with a good hole in a very plane surface. Figure 2 shows holes obtained by this method.
Using the abovementioned method, boring was performed on metal sheets such as Mo, Pt, Fe, Ni, Ag, eu and brass 0.2 mm thick. Very round straight holes, as small as 20 p. in diameter, as deep as 5 times the diameter of the hole, with a deviation of only 0,5~1 p. from roundness and a taper of only 1",1.5 p. could be obtained.
This method will be useful not only in boring the objective slit of an electron microscope, but also boring illumination systems for electron microscopes, electron diffraction cameras and vidicons.
The author wishes to express his thanks to Professor T. Hibi, Director of the Institute, for kind encouragement through the progress of the present work.
* Reported at the Second Symposium of Society of Electron Microscopy. Japan, 1954.
Frequency-Linear Drive for Spectrographic Recorder W. E. DEEDS
The University of Tennessee, Knoxville, Tennessee (Received April 23, 1956)
A DRIVE system for a spectrographic recorder can easily be made which is accurately linear with frequency. If radiation
passing through the spectrometer is also passed through a FabryPerot interferometer, the transmitted radiation will exhibit intensity maxima, or fringes, at equal frequency intervals. If the transmitted radiation is detected and the ac signal is amplified it can drive the synchronous motor which drives the chart paper:
For normal incidence, the rate of appearance of fringes is 2d ti~es the spectrometer frequency-scan rate in em-l·seel, where d IS the plate separation in cm. For many applications, d can be chosen to give a satisfactory driving frequency.
If the spectrometer scanning rate is very slow, as it is for infrared grating spectroscopy, several methods can be used to in· crease the motor-driving frequency. The Fabry-Perot plates can have greater separation, within certain limits. The ac signal can be fed into anyone of several kinds of frequency multiplier. If a grating is being used, ultraviolet light in high order can be superimposed on the regular beam, since the frequency-scan rate is increased proportional to the order. A more highly dispersing element can be mounted on the regular dispersing element and used solely for the Fabry-Perot beam. Without changing the driving frequency, one can increase the power to the motor and decrease the gear ratio, within narrow limits, Or, one can dispense with the motor entirely and drive the chart paper in discrete steps with an electromagnetic stepping-ratchet. Finally, a separate oscillator, whose frequency is servo-controlled to maintain a constant rate of
FlG.1.
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544 NOTES
appearance of Fabry-Perot fringes, can be employed to drive the spectrometer, as shown in the block diagram of Fig. 1. This last method is probably less desirable than the others.
A scaling circuit can be used to provide a marker signal for the recorder every time N fringes have passed, N being presumably a large integer. This has two advantages over the practice of recording the direct output of the Fabry-Perot: the marking pips are sharper, and the spacing can easily be changed.
Electrical Contact for High Vacuum Systems* ROBERT GOMER
Institute for the Study of Metals and Department of Chemistry, University of Chicago, Chicago, Illinois
(Received April 9, 1956; revised version received May 7, 1956)
I T is frequently necessary to establish permanent electrical contact with internal glass surfaces that have been rendered
conducting by metallizing or other means, without impairing the vacuum properties of the apparatus. While there is no difficulty in making vacuum tight tungsten through Nonex seals, contacts between the tungsten and the conducting surface are often troublesome. Most spring contacts anneal after repeating baking, while platinum or silver connections as ordinarily made, by painting over the electrode area after the tungsten wire has been sealed in, tend to open by mechanical fissure or sintering. The wetting angle of glass on tungsten seems to exceed 90°, resulting in a gap, which appears to be bridged, rather than filled by the metallic film. Electrical contact thus rests on a slender and fragile bridge.
The present method seems to avoid these difficulties and provides a contact with resistances from 2 to 15 ohms suitable for ultrahigh vacuum work, that can be baked out repeatedly, and functions at 4.2 oK. Permanent electrical contact is made by collapsing a platinized Nonex sleeve onto a strip of thin platinum foil,
Tungsten
b
(a)
Electric Contact
(b)
FIG.!. Vacuum tight electrical lead-in. (a) Ready for sealing. Platinum coating extends to point b. (b) Finished seal. Sealing in is started at point a and continued until Nonex sleeve has collapsed to point c.
"-'1 mm wide and "-'5 mm long. The resulting seal is mechanically and electrically satisfactory, since it provides for a large contact area between the electrode and the film, without requiring the latter to "leave" the glass surface at any point. Vacuum tightness is obtained by collapsing an unplatinized section of the Nonex sleeve onto a beaded tungsten wire, to which one end of the platinum foil is spotwelded. The method of preparation and the finished seal are shown in Fig. 1. The Nonex sleeve may be platinized conveniently with Hanovia liquid platinum paint. In a variation of the method, suitable for small tungsten wires, the platinum foil is wrapped around the wire and secured by spotwelds. The Nonex sleeve is then collapsed onto the platinum covered tungsten wire, which may project into the interior of the apparatus.
* Supported in part by a grant from the Petroleum Research Fund of the American Chemical Society.
Kneecap Gauge Foot WILLIAM C. SHAW AND S. P. FURMAN
U. S. Naval Ordnance Test Station, China Lake, California (Received April 30, 1956)
T HE "Kneecap" gauge foot was designed for dimensional gauging of specimens of relatively soft or porous material
having a curved contour surface. It is also useful with hard materials, and the principle employed may be applied to the design of cam riders for use in computers. The device has two characteristic advantages over conventional gauge feet; namely, the foot automatically orients itself relative to the curvature of the specimen; and the contact surface is comparatively large, thus minimizing deformation of the specimen from contact pressure.
The purpose of a gauge foot is to accurately specify one coordinate dimension on a surface as a function of one or two other coordinates. Such measurements can sometimes be satisfactorily obtained with a very sharp point or edge serving as a gauge foot.
W J: ><! -' u.. o
'" t) o I(f)
o <l W I
CENTER OF HEMISPHERE CONTACTS VARIOUSLY ORIENTED CONTOUR2.
DI AL GAGE LEG
CENTER OF ,I FOOT SURFACE
MAGNETIC LEG EXTENSION WITH CONICAL CAVITY AT END ENGAGING FOOT
-------- - ...........
SURFACE OF SOFT MATERIAL BEING MACHINED TO A PRECISE CONTOUR
AXIS OF B!;VOLUTIO~L
FIG.!. Sketch showing operation of the kneecap gauge foot.
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