ISSN:0034-6748    

DOI:10.1063/1.1770360

出版商:AIP    

年代:1945

数据来源: AIP

摘要:

The design and construction of a rapid‐response vacuum thermocouple for use in an infra‐red spectrograph is described. The thermocouple is made by condensing 600–1000A thick layers of Bi and Sb, which overlap slightly to form the hot junction, on a 400–500A thick film of Formvar. This film is stretched over a glass form having an opening under the hot junction. The hot junction is blackened with gold evaporated in H2at 2–4 torr. (1 torr=1 mm Hg.) The thermocouple is intended for use with radiation interrupted at frequencies between 1 and 5 hertz. (1 hertz=1 cycle per second.) It is shown that the signal‐to‐noise ratio of the thermocouple, defined as the ratio of the interruption frequency component of its output to the square root of its resistance, is the only criterion of its goodness, and that in an infra‐red spectrograph a single junction thermocouple has a greater signal‐to‐noise ratio than a multijunction thermopile. An important operation in the thermocouple construction is the use of a glow discharge before condensation of each metal to reduce the thermocouple resistance by factors of 5 to 10. Such a thermocouple has a resistance of between 20 and 50 ohms, a d.c. sensitivity of 6–7 microvolts per 10−4‐watt cm−2, and an output under radiation interrupted at 7 hertz of not less than one‐half the d.c. value.

ISSN:0034-6748    

DOI:10.1063/1.1770361

出版商:AIP    

年代:1945

数据来源: AIP

摘要:

The design and construction of a low frequency vacuum tube amplifier capable of detecting 5·10−10volt is described. The amplifier is intended to measure the alternating output of a rapid‐response thermocouple in an infra‐red spectrograph, the incident radiation being interrupted at frequencies between 1 and 5 hertz. (1 hertz=1 cycle per second.) The inherent noise level of the amplifier is less than the thermal noise of the thermocouple. This low amplifier noise level is attained by use of an excellent high gain input transformer, by careful selection of the first vacuum tube and operating its heater at low current, by use of inverse feedback, and by use of two power supplies, one for the heaters in series and a second for the plate and screen potentials, both of which have very good electronic voltage regulators. The noise level is further reduced by the use of inverse feedback and twin‐T resistance‐capacity networks to give a narrow and variable band width. The amplifier is operated from the a.c. power line. It feeds a short period galvanometer whose entire swing is recorded photographically so that the record has the appearance of a modulated carrier wave. A portable microammeter fed from a vacuum tube voltmeter is used as a visual monitor of the output. A simple photoelectric test signal generator is described, and typical records show the amplifier noise as well as its output for input signals as low as 6·10−10volt. The effect of too narrow a band width on the recording time of an absorption spectrum is discussed briefly and is illustrated by water vapor spectrum records.

ISSN:0034-6748    

DOI:10.1063/1.1770362

出版商:AIP    

年代:1945

数据来源: AIP

摘要:

In the study of thixotropic substances and of materials of non‐Newtonian behavior, it is important to obtain complete flow curves (rate of shearversusshearing stress) which are taken in accordance with a standardized procedure. The time interval for any given increase or decrease in rate of shear should remain constant. A recorder which draws complete flow curves has been developed as an attachment for a Couette type of viscometer. The deflection of the bob, which is proportional to the shearing stress, is plotted against the speed (r.p.m.) of the cup which is proportional to the rate of shear. For precise measurements the bob suspension spring must not be subjected to any friction load; therefore the recorder uses sparks generated by a high voltage to puncture the recording paper. The sparking electrode is moved by the bob deflection spring while the paper is moved perpendicularly to the electrode motion by the transmission handle, the position of which controls the cup speed. A number of measurements made with the recorder are shown. The recorded flow curves permit immediate interpretation and calculation (without any replotting) of the plastic viscosity, the yield value, and the thixotropic behavior of the tested materials. Also, a method is proposed for determining the plastic viscosity and the yield value at initial agitation, which are identified as ``the initial thixotropic viscosity'' and ``the initial thixotropic yield value.''

ISSN:0034-6748    

DOI:10.1063/1.1770363

出版商:AIP    

年代:1945

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1770364

出版商:AIP    

年代:1945

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1770366

出版商:AIP    

年代:1945

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1770368

出版商:AIP    

年代:1945

数据来源: AIP