Setting Of Resistance Research Articles

Calibration of gypsum blocks and data loggers and their evaluation for monitoring soil water status

The use of commercial data loggers and gypsum blocks to monitor the matric potential of water in soil was evaluated in the laboratory and at 2 field sites. A set of calibration resistors that simulated a matric potential range of —20 to —2120 kPa was developed that showed close agreement with data that was originally used to develop algorithms for the loggers. Data loggers used in experiments were calibrated against the resistors so output values could be re-scaled to that of the resistor set. Close agreement was found between the matric potential of soil, which was estimated from filter papers, and re-scaled logged matric potential values for gypsum blocks embedded in containers of soil maintained at a range of water contents in the laboratory. Re-scaled logged soil matric potential recorded at 2 field sites also compared favorably with filter paper estimates for soil sampled adjacent to where gypsum blocks were buried. It was concluded that, provided individual data loggers were standardised to the same matric potential scale using either calibrated resistors or soil of known matric potential, the gypsum block technique provided an economical and accurate measure of soil water status.

Quench protection system using a novel d.c. circuit breaker for LHD

The large helical device (LHD) has 12 superconducting coils that are strongly coupled with each other. The rating currents of these coils are from 13 to 32 kA and total magnetically stored energy reached 1.6 GJ. These coils are excited by six d.c. power supplies and each coil current is controlled with high accuracy to make a magnetic surface required for various plasma experiments. At the same time, it is required that these power supplies discharge the stored energy quickly when coil quench is detected. This paper introduces the quench protection circuit installed in the power supplies. For this system, a 30 kA and 2 kV class d.c. current breaker using the parallel connection of a small vacuum circuit breaker (VCB) and power fuse is developed. Also, the best discharge resistor set, that dumps stored energy in the wide operation range of the LHD without changing connection, is found using numerical simulation. To confirm the reliability of quench protection and operation delay, operating tests are done using an actual quench protection system and power supply. In this test, more than 400 shots for three deference power systems are finished without any operation failure.

Nonlinear digital-to-analog converter-discrete analog of a sine-cosine potentiometer

This article examines the principle underlying the design of the discrete analog of a sine-cosine potentiometer. The analog is constructed using a linear digital-to-analog converter and a set of resistors with switches that can be used to approximate sine and cosine functions over equal intervals.

Resistor assemblies for NEC accelerators

Resistor assemblies have been under test in the 14UD Pelletron at the Australian National University in Canberra, Australia since February 1988, with no failures. A full set of resistors was installed in March 1989 and their performances has been satisfactory. The design incorporates coaxial shielding and individual mounting resulting in excellent flexibility in installation and maintenance. A pair of resistors is used to span each insulated gap. The design can be easily adapted to other types of accelerators.

A distributive method to increase the analogic output (D/A) resolution of a microcomputer

This paper describes a simple and efficient method to increase the D/A output resolution of an 8-bit microcomputer, as exemplified on the Apple II. The “distributive method” can increase the final output resolution up to 32K with two 8-bit analogic channels. A simple interface based on balanced sets of resistors and driver software are described. Some applications are also reported.

Microcomputer-Based Payload Checkout System

A microcomputer-based system using Intel's 8085A microprocessor has been developed for the ground check-out of the rocket-borne instruments used for measuring electric field and electron density in the upper atmosphere. The complete system consists of an SDK-85 microcomputer, a 10 nA to 0.5 mA current source, an exponential sweep-frequency generator and analogue I/O modules. In addition to this, an audio cassette recorder and a printer are also included in the system.The sweep-frequency generator sweeps the entire frequency range of 50 Hz to 5 kHz in exponential steps. The current source has been realized by a set of resistors connected to a voltage source through programmable FET switches and is used for the calibration of a Langmuir probe payload. The audio cassette recorder is being used for mass storage of programmes and data.

Self-Checking Resistive Ratios

The two resistors which form the ratio are constructed as two separate networks of nominally equal resistors. Each network is chosen such that there is a dual network which can be constructed from the same set of resistors. Two configurations with the same nominal ratio are obtained by switching each network to its dual and interchanging their positions in the ratio. The mean ratio is a very close approximation to the nominal value. As an example, it is shown that only six resistors are required to produce all steps of a single-decade voltage divider with a mean accuracy of 1 in 106 using resistors adjusted to 1 in 103.

A Statistical Experiment Using Resistors

In undergraduate laboratories we frequently ask the student to use error theory to evaluate his results without giving him the opportunity to measure and analyze a large statistical sample to see how well it follows theoretical models. In the experiment described here, the student investigates the statistics of a set of resistors. In the process he gets some practice in the use and interpretation of histograms, and gains some insight into the relation of the Gaussian error curve and a real statistical distribution as well as the significance of standard deviation and standard error..

The traveling-wave v-antenna and related antennas

An investigation was made of the traveling-wave V-antenna, which is a combination of a traveling-wave antenna and a V-antenna. This paper includes a description of the antenna, a discussion of the effect on the radiation patterns of variations in such quantities as the loading resistance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</tex> , the apex angle <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Delta</tex> , the length <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</tex> of the traveling-wave section and the length <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h_{T}</tex> of the standing-wave section. Tests were also made on traveling-wave V-antennas with more than one set of resistors. An excellent agreement between the theory and experiments of the radiation patterns was obtained.

The Accuracy of Series and Parallel Connections of Four-Terminal Resistors

The range and accuracy of resistance calibration can be increased by the use of series and parallel connections of four-terminal resistors. Low value resistors can be permanently connected in series and reconnected in parallel by using Hamon's1 technique to change resistance level without materially affecting resistance accuracy. The resistors are connected in parallel by attaching shorting bars to one terminal at each end of each resistor and attaching matched resistors in series with the other terminals. High accuracy can be attained even though lead and connection resistance are relatively high. The purpose of this paper is to provide a theoretical base and an error analysis to justify the use of the series-to-parallel transfer technique at low resistance levels. The analysis uses a four-terminal equivalent circuit suggested by Searle.2 The accuracy of series and parallel connections of groups of like resistors is investigated in terms of the equivalent circuit. Procedures are developed for determining the connection accuracy of a set of resistors in parallel or series.

Thermal Converters for Audio-Frequency Voltage Measurements of High Accuracy

The ac-dc differences of a reference group of thermoelements have been evaluated at audio frequencies to a few parts per million (ppm) at currents from 5 to 20 mA. A technique for comparing the ac-dc differences of two thermoelements with an uncertainty of about 2 ppm has been developed. Two 5 mA thermoelements are used with a plug-in set of resistors of computable reactances to form thermal voltage converters for voltage measurements. With this same technique adjacent ranges of these converters can be compared to step up from 0.5 to 500 V to better than 10 ppm.

The Realization of RC N-Ports

Given an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n \times n</tex> matrix, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z(s)</tex> composed of elements which are the ratio of polynomials in the complex quantity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</tex> , necessary and sufficient conditions of a general nature are found which are required for the existence of a common-ground network of resistors and capacitors that possesses <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z(s)</tex> as its open-circuit impedance matrix. Based on these conditions, we consider a form of this problem in which the main restriction is the requirement that the elements of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z(s)</tex> have no more than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n + 1</tex> poles. The solution presented provides a practical procedure for determining whether a given nth-order matrix with no more than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n + 1</tex> poles can be realized, and if it can be, then an economical set of resistors and capacitors is derived. Further, a complete class of equivalent realizations is also presented.