Volume 17, Issue 10, October 1946
Index of content:
17(1946); http://dx.doi.org/10.1063/1.1770396View Description Hide Description
A high voltage meter employing a capacity divider can be used even for d.c. measurements if it is combined with a special automatic grounding device. The construction of an instrument covering the range 2–100 kv is described. Applications and further improvements are discussed.
17(1946); http://dx.doi.org/10.1063/1.1770397View Description Hide Description
The use of potentiometers in automatic electrical computing devices has necessitated a great improvement in commercial wire wound potentiometers in order to meet exacting requirements. For example, the use of ``end resistors'' has made it necessary to hold both the over‐all resistance and the resistance gradient to close tolerances. The accuracy must not only be of a high order, but it must be sustained throughout a long operating life. Methods used to improve performance, including the use of noble metal alloy contact materials, are discussed in this article.
17(1946); http://dx.doi.org/10.1063/1.1770398View Description Hide Description
The instrument described was developed to integrate and record the Massachusetts Institute of Technology Cyclotron beam current, for both the probe and the external target. Probe target currents are found by use of voltages developed by a thermopile which measures the temperature rise of the target cooling water; external target currents are measured directly by the voltage drop across a 10‐ohm resistor, in parallel with the 10‐ohm input impedance of the integrator itself, connected between the external target and ground. The instrument is essentially a stable, high sensitivity, linear a.c. amplifier, with a low impedance input, and a mechanical inverter for the d.c. input signal. Integration is accomplished by a standard a.c. watthour meter, and recording by means of a 5‐ma, d.c. pen recorder. The amplified signal is also used to operate a warning system to indicate audibly a change in the beam current.
17(1946); http://dx.doi.org/10.1063/1.1770399View Description Hide Description
An instrument is described which is capable of measuring one part of helium in 400,000 parts of other gases. The instrument is built around a 180° type mass spectrometer tube which is prefocused for helium ions. Use is made of this high sensitivity tube to locate leaks in vacuum equipment. The leaky container can be connected and evacuated by the pumps in the unit. A fine stream of helium played over the surface of the container will enter the leak and register immediately on the output meter. Very small leaks can be located easily to within a quarter of an inch. The unit is completely self‐contained, requiring only a line connection to a 110‐volt a.c. outlet.
17(1946); http://dx.doi.org/10.1063/1.1770400View Description Hide Description
An instrument for measurement of the magnetic properties of samples of small cross‐sectional area is described. The signal from two opposed pick‐up coils, one of which contains the sample, is integrated, amplified, and applied to the vertical deflecting plates of a cathode‐ray oscillograph. Each of the pick‐up coils lies in one of a pair of identical magnetizing solenoids. The signal from a non‐inductive resistance in series with the solenoids provides the horizontal deflection for the cathode‐ray oscillograph so that the hysteresis loop of the sample is displayed on the fluorescent screen. The instrument is well suited for measurement of the magnetic properties of samples having cross‐sectional areas of the order of magnitude of 10−5 cm2.
17(1946); http://dx.doi.org/10.1063/1.1770401View Description Hide Description
A ring‐of‐ten circuit is described, using ten pentodes, ten twin‐triodes, ten resistors, and no condensers, per ring. Two pairs of input terminals are provided for clockwise and counter‐clockwise feeding, respectively. This circuit can be used for electronic adding and subtracting, as well as for differential counting‐rate measurements on two sources. With the addition of five resistors to a ring, the number of counted events can be indicated on the screen of a small cathode‐ray tube. This circuit counts up to 5×105 evenly spaced events per second.
17(1946); http://dx.doi.org/10.1063/1.1770402View Description Hide Description
This paper deals with the methods and equipment used in the construction of small high speed bolometers. Particular attention is given to the Type G unit which is rugged, sensitive, and capable of being used satisfactorily with radiation modulated at 30 cycles per second. Special units can be used at considerably higher frequencies. Descriptions are given of methods and equipment for making the cellulose nitrate supporting film and for evaporating thin strips of gold onto this film.Deposition of electrodes and methods of testing for noise and sensitivity during the course of production are described. The use of metal back plates, separated from the bolometer strip by a small distance, is shown to be advantageous. With this construction, and a gas pressure of 20 mm of nitrogen, very satisfactory frequency characteristics are obtained. Gold black is used to increase the absorption of radiation in the vicinity of 10μ. It is pointed out that by controlling the gas pressure either resistive or conductive layers of gold black can be made. In the latter case it is possible to omit the underlying gold strip entirely. Photographs and descriptions of the equipment used for processing bolometers in batches of ten are given, and some of the more interesting points are described in detail. Data are given on frequency characteristics, useful life, and resistance to shock and temperature effects. Finally, brief comment is made on bolometers made of metals other than gold.
17(1946); http://dx.doi.org/10.1063/1.1770404View Description Hide Description
Two possible modifications of the original Kerst induction accelerator are suggested, each of which allows one to double the energy of the electrons. The equation of the instantaneous circle, deduced by elementary considerations under rather general assumptions, is applied to different particular cases. The effect of the anharmonicities introduced by the magnetization curve of the iron is discussed; the different types of induction accelerators are compared with each other.
17(1946); http://dx.doi.org/10.1063/1.1770405View Description Hide Description
This paper contains a survey of the characteristics and uses of non‐linear circuit elements in the generation of wave forms particularly useful in precision timing circuits. The use of these non‐linear circuit elements in detection and time measurement is also included.
17(1946); http://dx.doi.org/10.1063/1.1770407View Description Hide Description
An oscilloscope with a single‐sweep circuit may be used for recording transient currents. If the current changes 1 ampere per microsecond, the oscilloscope shunt may need to have an inductance as low as .02 microhenry. An inductance tenfold lower than this can be obtained easily with a tubular resistor with a coaxial return conductor and coaxial potential leads to the oscilloscope. The resistance is provided by a layer of metal on a glass tube. Pt, Cu, and Ni have been used. Such a shunt was used to record the discharge currents of three condensers. Reasonable agreement between measured and computed currents was obtained.