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代写英国硕士论文-HAROLD EDGERTON IN WORLD WAR II( The Structure of E(3)

时间:2012-05-23 14:02来源:未知 编辑:留学生作业 点击:
and focused on his interests from before the war and intensified his underwater endeavors. A close scrutiny of these three periods gives an effective and vivid picture of changes in Edgerton抯 work i

and focused on his interests from before the war and intensified his underwater endeavors. A
close scrutiny of these three periods gives an effective and vivid picture of changes in Edgerton抯
work in terms of his work environment, the scale and magnitude of his technology, and the
broadening of applications for his technology. Thus, an examination of Edgerton抯 pre-war,
wartime, and post-war efforts illuminates the influence that World War II had on his work.
PRE-WORLD WAR II
Between 1927 and 1939, Doc Edgerton moved from using the stroboscope purely as an
observational aid, to creating a new school of technology based on electronic control of sudden
power discharge into a flash tube. During this time, he built on his original work by improving
the accuracy and the robustness of the system and varying it in terms of speed, flashing
frequency and triggering mechanisms. In all cases and designs, the main goal was the same,
aiding the human eye in seeing something it could not otherwise. Capturing a snapshot of a
moment in time was the main goal of Edgerton's technology before World War II. During this
period all his designs contained a crucial ingredient, the basic strobe technology.
THE BASIC STROBE CIRCUIT
A great deal of Edgerton抯 work evolved from his innovation to the stroboscope. Invented in
1832, the early mechanical stroboscope was simply a disk with slits at regular intervals. As an
observer looked at a moving subject through the slits in the spinning disk, he could see
successive stages of the subject抯 motion. Edgerton抯 innovations in the stroboscope were in the
areas of electronic control and trigger mechanisms. His electronic stroboscopes could emit
flashes of extremely short duration and at a high rate under precise control. The control
mechanism defined the length of the flash. This was an important design parameter determined
by the speed of the subject such that the photograph could capture an instant of the motion
without blur. The trigger system was an accurate way of synchronizing the flashes with the
motion of the subject. The fundamental technical purpose of a high-speed flash system, whether
employed as a viewing device or a photographic tool, is to overcome the human eye抯 inherent
inability to 搒ee?and therefore study fast motions as they occur. These motions would normally
be a blur to the naked eye.
Pre-War WW II Post- World War II
1926 1939 1947 1963
7
Figure 5 shows a circuit representation of Edgerton's strobe system. This basic circuit was
adapted for all of his electronic flash applications. The charging resistor RC limits the current
flowing through the capacitors during charging. The trigger switch is initially open, and the trip
capacitor C1 is charged to a voltage Vs. Vs is determined by the voltage divider composed of R1
and R2 and E, the voltage of the power source:
1 2
2
s
R R
R
V E
+
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When the switch closes, the energy in C1 is pulsed into the spark coil, and a voltage is applied to
the trigger electrode wrapped externally around the flash lamp. This excites the noble gas in the
tube (typically xenon) and decreases the breakdown voltage of the gas. When the voltage across
capacitor C is greater than the gas' breakdown voltage, the gas in the tube will ionize and create a
brief flash of light.
Characteristics of the flash such as intensity, duration, and recharge time can be controlled by
changing the values of the components in the circuit and the resistance of the tube (by using a
different gas). The flash duration is approximately given by 椒R稢, where R is the resistance of
the tube. Flash duration for Edgerton抯 electronic flash 搑anged from 1/3,000 to 3/10,000,000 of
a second.? The extremely short flash duration made possible by the electronic strobe is ideal for
high-speed photography. The flash duration of the stroboscope allows the photographer to
achieve exposure times much shorter that those permitted by a mechanical shutter, since the film
is exposed only when the flash illuminates the scene. However, the light output of the flash has
to be high enough to provide adequate light on the subject, and the subject has to be illuminated
long and intensely enough so that the image will be well-exposed on the film. The desired flash
duration should also be as short as possible to avoid blurring. These strobe parameters can be
tailored to the applications for which the strobe is used. For example, the bullet photographs
7 Harold Edgerton, Electronic Flash, Strobe (Cambridge: The MIT Press, 1983), 7.
8 Edgerton, Stopping Time, 44.
Figure 5: Basic Electronic Strobe Circuit7
8
require flash duration of 1/1,000,000 of a second, whereas hummingbird photos can be taken at
1/100,000 of a second. As a young researcher at MIT, Edgerton invested a lot of time in refining
his electronic flash and utilizing it in a variety of applications.
PRE-WAR APPLICATIONS OF THE STROBOSCOPE AND EDGERTON扴 WORK AT MIT
Edgerton抯 research and his technological focus were influenced by
changes that were taking shape at MIT. The head of the Electrical
Engineering Department at MIT, Dugald Jackson promoted new
research areas that branched off from the department抯 main focus,
power systems.10 The stroboscope was an example of the type of
research that Jackson had in mind. Thus, Edgerton continued working
at MIT following his graduation in 1931 to further his work on
stroboscopes.
Edgerton抯 plan to stay at MIT coincided with the 1929 Great
Depression, which negatively impacted the entire nation. In the early
1920抯, Karl Compton, who later served as president of MIT from
1930-1948, began promoting his vision for the Institute to become the hotbed of scientific and
technological developments, rather than being an industry-focused technical university. The
association with industry was very strong at this time. For example, the advisory committee in
charge of the engineering department抯 curriculum was composed of leaders in the industry from
companies including GE, Edison Illuminating Co. of Boston, American Telephone and
Telegraph Co. of Boston, and Westinghouse. These corporations benefited from this relationship
since they had direct access to MIT抯 people and wealth of knowledge, which they could channel
to their projects.11 Although Compton wanted to change the Institute's relationship to industry,
the Depression halted his plans. MIT maintained its close ties with American industries to
sustain its financial situation and provide resources for growth. President Compton stressed
concern about MIT抯 dependence on corporate America:
9 Karl L. Wildes and Nilo A. Lindgren Wildes, A Century of Electrical Engineering and Computer Science at MIT,
1882-1982, (Cambridge: The MIT Press, 1985), 70.
10Ibid 70.
11Ibid, 43.
Figure 6: Karl Compton9
9
MIT抯 over-dependence on industry, and more specifically on
medium size corporations in technologically stable industries, had
led to a strong emphasis on practicality and immediate utility in
engineering education. It had transformed the Institute into a
trouble-shooting agency for industry and thwarted its autonomy.13
Despite Compton抯 concern, during the Depression years MIT had
no choice but to promote consulting for industry in order to survive.
This influence of corporate America on MIT research was reflected
in Edgerton抯 consulting work with companies that wanted to utilize
his stroboscope. Thus, his ingenuity in applying his technology to
numerous applications was fostered by MIT and its role during the
Great Depression.
In 1931, with jobs scarce due to the Depression, MIT graduate
Kenneth Germeshausen came to Edgerton seeking a research position. Edgerton convinced
department head Jackson to hire Germeshausen as an assistant without pay and assigned the
former student to projects involving use of the strobe to find problems in industrial machinery.
Herbert Grier joined Edgerton in a similar fashion in 1933.15 Together, they established an
informal partnership over the years. One of their first consulting
jobs was with a paper mill company in which the machinery
moved too fast to observe the cause of the defects. Using the
stroboscope and high-speed motion pictures, they were able to
observe the motion of the machine and see where the defects were
forming.16 The stroboscope was also useful to engineers who
sought to observe fast machinery while in operation. With
Edgerton and his colleagues?help, companies such as the Russell
Box Company and the Foster Winding Machine Company utilized
Edgerton抯 stroboscope to record high-speed motion of their
machinery in action. Figure 7 shows a thread machine captured in
action by the stroboscope. For this type of work Edgerton
licensed his patent to General Radio Company in 1935 to build the
hand-held Strobotac (Figure 8). This 12-pound strobe unit could
flash up to 14,400 times a minute.
In addition to industrial clients, Edgerton also cooperated with other departments within MIT.
Figure 9 shows his work for the Mechanical Engineering department in which he examined the
movement of air through the blades of a fan. In one of his reports to the Electrical Engineering
department, Edgerton listed the 揅lass of Customers?he had for his stroboscope units and work



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