摘要:

The lecture is a general survey of recent developments in the field of fixed and variable resistors. The period covered is the previous four years. It is concerned primarily with British component development, but some reference is made to work done in other countries, notably the United States.

DOI:10.1049/pi-b-2.1962.0002

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Current noise in fixed resistors is usually expressed empirically in terms of current and resistance, but performance of different materials from which resistors can be constructed must be specified in terms of current density, resistivity and geometry. It is argued from the theory of dimensions that there should be a relationship between the index of frequency dependence and the index of resistance dependence. It is not clear how this can be associated with an experimentally observed relationship between frequency index and voltage coefficient. Secondary effects arise from any local concentration of current, and the order of magnitude of the associated temperature rise can be estimated from the potential difference across the contact by Holm's theory of point contacts.

DOI:10.1049/pi-b-2.1962.0003

出版商:IEE    

年代:1962

数据来源: IET

摘要:

The paper is in two parts. In the first part a rough calculation is made of the temperature distribution along the length of a rod, and it is shown that this is affected by the length of the terminal lead. A comparison is made between calculated and observed temperatures and there is good agreement. In the second part the temperature of a pyrolytic carbon film is calculated when subject to a rectangular pulse of energy, the range of pulse length being 0.1–100μs. From these calculations a rating is derived for a number of commercial types of resistor. It is shown that, if a limitation of 1000 V per inch of film is applied, this largely overrides any limitation based upon the instantaneous temperature rise of the film and this has to be taken into account only for pulse lengths greater than 10μs and on resistances of the order of a few tens of an ohm.

DOI:10.1049/pi-b-2.1962.0004

出版商:IEE    

年代:1962

数据来源: IET

摘要:

The causes of long-term failure under practical conditions of use or storage of different types of fixed resistors commonly used in electronic equipment have been investigated. Some reported life tests have proceeded without interruption for almost four years. Carbon-composition (grade 2) resistors under load fail by slow thermal degradation of the resistive material. Drift of value may also occur if unloaded resistors of this type are stored in a damp atmosphere. Vitreous-enamelled wire-wound resistors made with fine wire may fail during tropical exposure both unloaded and especially when lightly loaded with direct current. This is owing to electrochemical corrosion taking place at faults in the vitreous coating. High-stability cracked-carbon (grade 1) resistors may fail rapidly under light d.c. load by electrochemical action if moisture condensation occurs and the protective paint or varnish coating is inadequate.Tests for long-term resistor stability are critically discussed.

DOI:10.1049/pi-b-2.1962.0005

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Resistors may be formed from silicon both from the bulk material and by forming on the surface of the silicon diffused regions which are isolated from the bulk by ap–njunction. This isolation is incomplete owing to leakage current and capacitance in the junction and to field-effect transistor action. Noise in silicon resistors should not be much larger than the Johnson noise except where noise is introduced at the contacts. Contacts having linear current/voltage characteristics may be made to silicon either by the formation of a highly doped layer of the same type or by the formation of a region of high minority-carrier recombination at the contact. The chemically reduced nickel contact is of the latter type. Experimental results are presented to show that it may prove adequate as a contact material for resistors under suitable conditions. A method for making such resistors is described.

DOI:10.1049/pi-b-2.1962.0006

出版商:IEE    

年代:1962

数据来源: IET

摘要:

During the life of a temperature-sensitive resistor (t.s.r.), two processes are at work producing permanent changes in body resistance. One gives an increase in resistance, and is thought to be crack propagation; with constant current loading, it can result in failure by fracture. The other process gives a decrease in resistance, and is thought to be continued reaction of the constituent oxides; with constant current loading, it can result in resistance stabilization. With normal current loadings, the approach to failure with life of an unprotected rod can proceed at a rate such that the ‘cold’ resistance is nearly proportional to the square root of lifetime. Operational lifetime of a rod is defined as the time required for the ‘cold’ resistance to increase by 15% with constant current loading. The corresponding current rating decreases logarithmically with the required operational lifetime. On this basis, the current rating of a particular rod should be reduced by at least 50%. This need for a reduction in rating is in accordance with the results of conventional life tests.There seems to be little justification for the popular assumption that the rod form of t.s.r. is intrinsically a much inferior component to the bead. This view is an unfortunate consequence of the relatively very different rating standards adopted for the two items. Continuous operation of a typical rod at a current twice the rated value reduces its life by a factor of 20 to about 100h. On the other hand, continuous operation of a bead at the original rating gives a life of more than 10000 h. Suitable derating of the rod would eliminate the apparent difference between the two forms.

DOI:10.1049/pi-b-2.1962.0007

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Voltage-sensitive resistors which utilize the inherent properties of semiconductor junctions to achieve useful non-linear properties are generally referred to in the United States as diodes or varistors. Which term is chosen depends on the symmetry of the voltage/current characteristic of the device. If it is non-symmetrical with respect to the origin of the co-ordinate axes, it is a diode; if it is symmetrical, it is a varistor.The paper presents the electrical and thermal characteristics, as well as the general method of fabrication, of a variety of diodes and varistors which have been developed over the past five years. Included are devices intended for use as regulators, limiters (both fractional-voltage and multiple-voltage), surge and lightning protectors, modulators and demodulators, and voltage references. Comparisons are made between voltage-sensitive resistors made from copper oxide and silicon carbide and new devices, particularly those made by diffusion techniques in silicon.For critical voltage-reference applications, diodes have been developed which have extremely low temperature coefficients, comparable to the best standard references now available. A description of these, and of the reliability of semiconductor diodes in general, is also given.

DOI:10.1049/pi-b-2.1962.0008

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Typical applications for small low-power high-voltage resistors are outlined, and the properties of the solid carbon-resin, solid carbon-rubber and carbon-resin film resistors used in these applications are briefly considered. Various parameters used to indicate non-linearity are compared, and the problem of maintaining accurate voltage division over a range of applied voltages is discussed. The development of improved high-voltage resistors for use in the potential-dividing chain of a large electrostatic generator, where the components had to withstand the effects of occasional very-high-voltage surges, is described.This improved performance was obtained from resistors by utilizing a film of conducting tin oxide protected with a covering of high electric strength and by including an internal spark-gap. These resistors are useful for high-voltage applications generally, and their behaviour on test is briefly described.

DOI:10.1049/pi-b-2.1962.0009

出版商:IEE    

年代:1962

数据来源: IET

摘要:

A quantitative comparison is made between the results of the perturbation-theory analysis and experimental observations. It has been necessary to consider only the fundamental mode of propagation in a waveguide containing an equivalent dielectric slab and to use as the perturbation the change in the diagonal component of the ferrite permeability tensor as the ferrite becomes magnetized. An explicit expression for the phase shift is derived. A simplified form valid for ferrite specimens large enough to be useful in the reciprocal phase-shifter reveals the principles of operation. This result shows that dielectric concentration of the microwave fields within the ferrite produces a magnification of the permeability change as the ferrite specimen becomes magnetized in the small applied d.c. field.

DOI:10.1049/pi-b-2.1962.0011

出版商:IEE    

年代:1962

数据来源: IET

摘要:

It has been theoretically predicted and experimentally verified that spin-wave instabilities can be excited in a ferromagnetic material when a microwave magnetic field is applied parallel to the d.c. field. The paper presents a summary of a plane-wave theory concerning this phenomenon and the results of the experimental verification of it. The utilization of the phenomenon as a new investigation tool for the study of relaxation mechanisms in ferromagnetic materials is discussed and the possibilities of application in the field of microwave devices are considered.

DOI:10.1049/pi-b-2.1962.0012

出版商:IEE    

年代:1962

数据来源: IET