Relay Contacts Research Articles

The erosion of relay contacts

The wear of relay contacts is chiefly electrical and due to discharges occurring when the contacts are opened and closed. Arcs cause more damage than do glow discharges and account for most of the damage. Short arcs at relay contacts are of two types which predominantly erode respectively the anode and the cathode. The type of arc which occurs and its duration are enormously influenced by foreign material on the contact surfaces. The chief source of foreign material in many applications is organic vapor from the atmosphere, which can be decomposed to form surface carbon. Thus the atmosphere in which relays operate is often of great importance in determining their performance. These various factors influencing the wear of relay contacts have been isolated and are now quite well understood.

Improving Temperature Control of ARL Model 2300

The ARL Model No. 2300 is a commonly used photographic processing machine in spectrochemical laboratories. Temperature control in this unit comes from a thermostat which by a relay energizes a solenoid valve on a cold water inlet when the bath temperature is too high. Bath temperature variations can be reduced if an additional relay contact is used to run the tray rocking motor of the machine whenever cold water is being admitted. The agitation which results decreases the over-shoot which otherwise can occur before the thermostat senses the lowered temperature. The only operational precaution is to switch on the rocking motor when a plate or film is to be developed even though the machine is rocking when the darkroom is entered. Otherwise the rocking may be turned off during a processing if the thermostat is satisfied.

Magnetic Analogs of Relay Contact Networks for Logic

Two techniques are described for designing multiapertured magnetic structures capable of realizing any specific logic function. The structures are made from rectangular hysteresis loop material. The designs are derived from the corresponding relay contact network by replacing each current carrying conductor in the relay circuit with its analog in the magnetic circuit, a flux-carrying conductor, replacing the emf with a pulsed mmf; and replacing each back contact with a saturable portion of the magnetic circuit in the topological equivalent of the contact network. A flux reversal through a saturated portion may then be blocked by means of an inhibiting Current applied to a suitable winding, the current representing a logical input variable. Thus flux may be ``steered'' through the magnetic circuit in a manner analogous to the steering of current through the contact network. For planar structures the first technique may be used to obtain the analog of series-parallel and bridge type circuits; parallel circuits. It is pointed out that the analog of a relay tree can be used as a standard structure suitable for realizing any Boolean function. Representative examples of both designs are shown, and experimental data are given.

Current distribution in the cylindrical source plane-electrode configuration

There are a number of instances in the operation of electric apparatus in which the physical situation may be approximated by a configuration in which a plane electrode conducts current which is received from or delivered to a cylindrical conducting path normal to its surface. Among these instances the most familiar examples are cases in which the conducting path is an ionized column resulting from sparkover (breakdown) of a solid, liquid, or gaseous dielectric between conductors, or the process of arc formation by the separation of initially juxtaposed conducting surfaces between which current is flowing. Typical situations correspond to circumstances accompanying insulation failures in apparatus, relay contact ���breaks,��� circuit-breaker operations, and to the sparkover phenomena utilized in electric spark machining.1���2 In each of these situations craters are formed on the electrode surface. Considerable attention3���5 has been given to the phenomena of crater formation for obvious reasons. Formation of the craters has been attributed to various causes1,5,6 and, indeed, the predominant cause may vary, depending on conditions of current formation, duration and magnitude, and on current-density distribution in the ionized column. In at least one range of physically realizable circumstances current density beneath the surface has been demonstrated3 to be significant in determining the depth of crater formed by a particular discharge. The relationship demonstrated was of a qualitative character only, however, owing to the lack of quantitative knowledge concerning both transient and steady-state subsurface current distribution. This paper describes the results of an analytical study of current distribution under appropriate conditions. In this study steady-state current distribution was determined from work by others on an analogous problem in hydrodynamics.7,8 Transient current distribution was determined by a solution which is described in some detail in the Appendix.

Fundamental Processes of the Short Arc

The short are develops an instability when certain critical conditions of power input to the are are not satisfied. In this unstable condition the are is momentarily extinguished, a molten filament of metal is drawn between the electrodes and this may permanently bridge the electrodes. Semi-empirical expressions have been derived which predict at what time in the life of an are it becomes unstable. These expressions give a simple explanation of some of the erosion characteristics of relay contacts. In addition, the analysis is useful in determining the optimum current waveform for percussion welding, where a stable are is desirable.

Static control in automatic warehousing

THE virtual elimination of relay contacts from the highly repetitive functions required for automatic warehousing was made possible by the selection of static control elements, Westing-house Cypak,1,2,3 in place of conventional relays for an extensive mechanized carton-handling installation in the Chelsea Milling Company premix food plant at Chelsea, Mich. While the basic concept of the control philosophy was determined to be the same for either relays or static control elements, the high reliability and negligible maintenance inherent in static control elements, which have no moving parts subject to wear or corrosion, dictated the choice. Interestingly, the first cost was found essentially comparable.

Minimizing Damage from Random Vibration

Damage is defined and examples are cited. Illustrative problems of relay contact arm chatter, gyro precession and noise generation, and stress fatigue in a structure are given. It is concluded that there are three means by which damage can be reduced: raising the damage threshold of the item, modifying the transmissibility of the intervening structure, or reducing the severity of the excitation. The examples are an attempt to show specifically how this can be done in practical cases.

Minimization of components in electronic switching circuits

Switching circuit synthesis presents two basic problems to the engineer. First, he must be able to obtain a circuit which will function according to the input-output specifications. Second, the circuit must be economical in the use of switching components, whether they are transistors, diodes, vacuum tubes, or relay contacts.

Relay Contact Behavior Under Non-Eroding Circuit Conditions

When palladium or platinum-family metal contacts are operated in an environment which includes organic vapors, the performance of the contacts may be seriously degraded. If the contacts open and close currents, the contact erosion may be increased enormously. On the other hand, if the contacts merely prepare the circuit and do not directly open or close the current flow, no erosion will take place. The contacts may then fail to conduct the circuit current satisfactorily, because of the formation of an insulating polymer-like film. This latter type of failure has been the subject of extensive studies at Bell Telephone Laboratories for the past several years and is the subject of this article. These studies have yielded a new understanding of the contact problem and resulted in certain changes in relay contacts to improve their performance under service conditions.

Arc Suppression for Relay Contacts in DC Service

Available relays for control of high-power direct current are seen to be large, heavy, and adversely affected by vibration and shock. This paper shows how commonly available components of reasonable size can be used with small vibration-resistant relays to control large direct currents at high potential. Thus, control of high-power airborne power supplies on the direct current side has become possible with reasonable equipment.

Activation of Electrical Contacts by Organic Vapors

Unreproducibility of earlier work on the erosion of relay contacts has been traced to the effects of organic vapors in the atmosphere. Carbon from decomposition of these vapors greatly alters the conditions under which an electric arc can be initiated and can be sustained. The importance from the standpoint of erosion comes from the fact that for many circuit conditions contacts activated by this carbon cannot be protected against severe arcing by any conventional capacitance-resistance network. This paper reports investigations which have enabled us to understand the activation of contacts by organic vapors.

Capability of sealed contact relays

A CIRCUIT designer contemplating the use of a relay must consider its operating characteristics and the reliability of its contacting function. The electric erosion causing contact wear gives rise to contact surface conditions permitting contact failure to open a circuit caused by locking; particularly in talking circuits, reliability can be further impaired by the operating environment which may contain corrosive elements, organic vapors, or mobile dirt, all of which increase the probability of failure to give contact closure. Unfortunately, the incidence of these factors affecting reliability is not predictable with respect to time or place. The considerations involved are not unlike those associated with electron tubes and transistors. Because of the growth in the complexity of electric switching systems increasing emphasis is placed upon the elimination of factors affecting component reliability. In the Bell System one means to achieve improved reliability has been the development of sealed contacts. Two types have reached application, both providing encapsulation to free contacts from the effects of environment; one type, in addition, circumvents the effects of electric erosion by employing liquid contact surfaces. The development of sealed contacts and relays using such contacts has been described elsewhere;1-4 the purpose of this paper is to consider some of their characteristics from the standpoint of application.

Several-valued combinational switching circuits

SINCE the introduction of symbolic methods1,2 into the field of digital control, much has been written on the application of Boolean algebra to the analysis and synthesis of 2-terminal electromagnetic (relay and magnetic core) and electronic switching networks. In general, a switching network involves not only the network configuration and the switching elements but also the states of transmission through the network. A survey of the literature will show however, that it is generally (tacitly) assumed that the states of transmission through a switching network are limited to two values. For relays the two states are usually the establishment and the opening of a d-c path through the network; for electronic gate circuits these two states are usually the presence and absence of a pulse. An essentially similar situation prevails on the states of the switching elements in a network. For relays, a relay contact is either open or closed; for electronic gates, an input or output lead either carries a pulse or does not carry one.

Magnetic logic circuits for industrial control systems

THE ELEMENTS of automatic control systems may generally be put into three functional categories: 1. Sensing or input elements, which convert external events into useful control signals. 2. Computing elements, which determine the mode of operation of the controlled system on the basis of input information. 3. Machine actuating elements, which convert the electric signals received from the computing elements into actual physical operations. Control systems can be further classified into two general types, analogue and switching. In analogue systems, input signals and output quantities are continuously variable. In switching systems, information is represented by discrete states of electrical or mechanical quantities. Most switching control systems employ a binary representation, in which only two signal levels are distinguished; this permits the use of components which have only two stable states. Relay control systems are the most common binary switching control systems now in use, and information is represented by the two distinct states of the relay contacts. The purpose of this paper is to describe new nonmechanical magnetic elements for use in binary switching control systems.

A transistorized overvoltage relay

PERHAPS the most important single protective device in any aircraft electric system is the overvoltage relay. Overvoltage conditions cannot only cause serious damage to connected load equipment and to the power generation equipment, if not removed, but can cause the loss of the entire electric power system. Overvoltage relays are designed to have inverse time-voltage characteristics because most of the damage caused by overvoltage is because of overheating. To obtain overvoltage protection and still not get nuisance operations on normal system transients, the relay must operate very rapidly on extreme overvoltages and relatively slowly on slight overvoltages. Upon completion of the time delay the relay contacts close the trip coil of the generator control relay, thus de-energizing the faulty system.

A polar relay using momentum transfer

A PRINCIPAL application of magnetic polar relays is to circuits where high operating speeds are required. One common approach for obtaining highspeed, bounce-free operation of relay contacts has utilized reduction of the armature size and mass. Disadvantages in reducing armature size are the resulting reduction of relay contact forces and the need for smaller mechanical tolerances.

Development of a wire contact relay

IN AN age where electronic devices are increasing in quantity and complexity, the electromechanical relay still plays an important part in various switching operations. Commercially available relays were formerly used in accounting machines but, with steady increases in machine speed and capacity, it became necessary to design an improved relay. The development of a wire contact relay for business machines applications is discussed herein.

A Telephone Switching Network and Its Electronic Controls

A high-speed telephone switching network with electronic controls is described. The high speed allows one-at-a-time operation, reducing both the number and complexity of control circuits. Germanium diodes, transistors, cold-cathode tubes and fast relays perform the control functions; glass-sealed relay contacts provide paths for speech. A laboratory model of the network has performed reliably for over three years.

Controls for Step Voltage Regulators [includes discussion

A unique control circuit for step voltage regulators is described. An auxiliary relay with four pairs of contacts has been eliminated; this results in reduced maintenance and quiet operation. Full integrating time delay is obtained by means of a motor-driven time-delay relay operated directly by the contacts of the voltage-regulating relay. Sparking on the voltage-regulating relay contacts is reduced to a minimum.

The recognition and identification of symmetric switching functions

IN the design of switching circuits based on relay-contact networks, it is known that if the function which describes the network is of the symmetric type it leads to a network which is much more economical of switching elements than the best series-parallel circuit. C. E. Shannon1 first described this type of function and its associated relay contact network in 1938. His definition of the symmetric function was general, but most of the generality of concept has been lost in subsequent treatment of the subject. For example, S. H. Washburn2 defines the symmetric relay-contact network as ?one in which the conditions for closing a particular input-to-output path are given & in terms of the number of relays operated and un-operated.? This particular type of network is derived from a restricted class of symmetric functions ? a class of functions which may be realized by means of iterative networks.3 There is a much larger class of symmetric functions contained within Shannon's definition, and these can be realized only by means of non-iterative networks.