Search

A modern form of mutual inductor that comprises windings on a dust core toroid can be applied to the classic Carey Foster bridge to measure capacitance, avoiding the older forms of fixed or variable mutual inductance. When hermetically sealed, these closely coupled inductors offer stability in the 0.25% class

It is shown that the varistor, a nonlinear resistor with current-voltage characteristics of the form i=ke/sup n/, can be used to achieve superior limitation of inductive transients over that obtainable with a simple diode, or with a diode plus additional linear resistance. To this end a transient analysis is made of the circuit composed of the inductor, its internal linear resistance, and a shunt varistor when the source circuit is opened. The resultant differential equation, though nonlinear, is integrable in terms of elementary functions, and general results are presented in mathematical and graphical form for the current and voltage transients. For all n>1, the transient is found to reach zero in a finite time rather than asymptotically. For a given voltage rise when the source circuit is opened (a basic design parameter), the Zener diode yields the shortest transient. Except for the lowest values of n, the varistor is shown to approach the performance of the Zener diode, while offering practical advantages. >

A temperature standard in the body temperature (clinical) region would be helpful in calibrating fever thermometers, now largely electronic. Temperature standards (fixed points) commonly use the freezing point of a pure material, often a metallic element. A check of the periodic table reveals only one suitable candidate, rubidium, which melts at 38.89/spl deg/ C(102.00/spl deg/F). Rubidium, however, is an awkward material to handle. A hydrocarbon plastic (polystyrene, polyethylene, polypropylene) would make a suitable container for the same reason. The device should require only a small quantity of rubidium. Detecting the melting/freezing transition should not be difficult, as rubidium has two helpful properties, either one of which may be used for the purpose. On melting its volume expands 3.7%, and its electrical resistivity rises 58%, from 14.21 to 22.52 /spl mu/ohm-cm. A unity ratio ac bridge might be used, one arm being a solenoid surrounding the rubidium container, and the other a solenoid surrounding a metal of similar dimensions, with resistivity intermediate between that of liquid and solid rubidium, e.g., tin-lead alloys. A three-coil arrangement of the type used in linear displacement transducers might also be used with the two metals. >

Universal circle diagrams are developed which represent the gain, input admittance, and output impedance of the cathode follower. The variables are transconductance and the components of cathode load. The Colpitts oscillator is considered as a cathode follower, and is analyzed with the aid of the circle diagrams, and also algebraically.

A solid state discriminator for the range 0.4 to 10 V is described. Tunnel diodes are used for the discriminator element and in a special fixed dead time circuit. An analysis of temperature stability is presented. The regulated power supplies are described, including a special negative resistance feature in the bias supply.

The optimum load resistance with respect to output voltage and the maximum voltage swing obtainable are investigated for a resistance-coupled triode voltage amplifier.