Analog Control System Research Articles

Whole-cycle control of AC power to small electric heaters

When a triac is used to control the flow of AC power to a heater, burst control is preferred to phase-angle control, but cannot be used if the thermal system reacts quickly to changes in heat input. This paper describes an arrangement which allows zero-voltage triggering of the triac, so avoiding the problems associated with phase control, but is usable with plants whose thermal time-constants are as short as 5 s (with 50Hz supply) or less. Its hardware requirements are no more than those of burst or phase control. Schematic circuits are given for use with both digital and analogue control systems.

User-Reconfigurable Digital Drive Controller

This paper describes an experimental high level language-based digital drive controller for use in numerical control and robot control systems as well as in general single and multiple drive systems. The controller is designed to replace conventional modular analog control systems. The controller directly executes a high level application-oriented graphic language ideal for real-time control in industrial automation. The high level language makes it possible for the user to configure the controller to his control application without difficulty, so reducing software costs significantly. A new architecture designed for high execution speed and a microprogrammed operating system allow the controller to be used for all control loops and also logic tasks in high performance multi-drive systems. Typical configurations for a d.c. motor controller are shown and experimental results are described.

Distributed Control Systems For Desalination

Historically, desalination applications have not utilized direct computer control due to the relative simplicity of the typical desalination control systems, the cost of direct computer control and the heretofore sophisticated operation and maintenance procedures required to implement a direct computer controlled system. As the size of desalination plants has increased for facilities in the Middle Eastern countries, the need for energy management and data acquisition have appeared in the form of ancillary computer systems in addition to the standard analog control system for the facility. The presentation will provide an overview of typical Distributed Control systems which have become more readily available in recent years. Emphasis is placed on the steps which have been taken by various manufacturers to simplify the implementation, operation and maintenance of currently available systems and the importance of monitoring significant process variables which affect operating efficiency and the physical condition of the plant.

Instrumentation in rolled–metal production

AbstractA discussion is presented of the similarities and differences between the steel and non-ferrous metals industries in their usage of instruments and analogue control systems to assist the production of rolled metals. A major difference between these industries, which dominates their attitude towards computer process control in particular, is the scale and continuity of production. Because of its smaller scale the non-ferrous metals industry is more interested in instrumentation and simple analogue control systems to improve the profitability of existing plant or individual items of new equipment. In addition there are differences and similarities in the detailed use of instruments. To illustrate this four specific examples are discussed briefly: instrumentation in hot rod rolling, recent developments in shape measurement, strip-thickness gauging, and instruments for weighing andfor width and length measurement.

Computer analysis of voltage controlled induction machines

This paper gives a brief description of the set of programs, elaborated recently for the analysis of three- phase voltage controlled induction motors, fed by back- to-back connected thyristor-thyristor or thyristor-diode pairs. The most interesting results of the computer analysis are also published. The set of programs is suitable for both exact calculation to check the steady-state parameters and analysis of dynamic performance. The eigenvalues of the transfer matrix are plotted in a speedtorque coordinate system. Tendency for a special subharmonic self-oscillation may be seen. Some characteristic root-loci are also represented. In addition the z-transfer function of the controlled motor, the design method of the analogue or digital control system are outlined.

Crystal weighing mechanism for growth monitoring of czochralski grown crystals

A sensitive lever mechanism capable of accurately monitoring the weight of a growing, rotating crystal boule is described. The low noise weight data can be processed by an analog control system or an automatic, digital, adaptive control system to grow a boule to a programmed diameter. The operational success depends on the frictionless mechanical multiplication of the load and electronic expansion of the transducer response. The resulting monitoring sensitivity has produced lithium tantalate, lithium niobate and neodymium gallium garnet boules of 22 mm diameter with ±0.4 mm variation over the length of the boule. The mechanism is schematically shown incorporated in a newly designed crystal puller to illustrate its functional uniqueness and potential adaptability to crystal pulling systems of other types.

A cloud chamber control system

We describe an analog control system for the temperature control of an expansion cloud chamber. During the expansion, the sample gas and the chamber walls are cooled at the same rate so as to maintain adiabaticity. The control system measures the wall temperature with transistor temperature sensors, calculates the gas temperature from the gas pressure using the adiabatic gas law, and generates a control signal proportional to their difference. The control precision is sufficient to allow the chamber to be used in the study of atmospheric phenomena.

A cryomicroscope for the study of freezing and thawing processes in biological cells

A cryomicroscope capable of effecting controlled freezing and thawing in biological cell suspensions has been developed. A dual capability for both heating and cooling is employed in conjunction with an analog control system to provide for precise regulation of the specimen temperature between 77 °K and 310 °K at time rates of temperature change between zero and several thousand degrees centigrade per minute. The microscope can be fitted with a high speed motion picture to record the dynamics of the freezing and thawing processes in slow motion. A miniature freezing and thawing system adapted to the stage of a light microscope enables a broad spectrum of cooling and warming rates to be achieved by cooling the specimen at a constant rate with a steady flow of refrigerant fluid through the system and by simultaneously dissipating electrical energy at a variable rate in a resistance heater immersed in the fluid stream and in thermal communication with the specimen. The control system is of the analog type in which a signal generator, inverter, and integrator are used to generate a voltage representative of the desired linear temperature profile, be it for cooling or warming. This profile is continuously compared in a summing unit with the amplified output of a thermocouple monitoring the specimen temperature. The output from the summing unit, which is proportional to the difference between the generated reference temperature and the specimen temperature, is amplified in a power amplifier having the resistance heater as its load. Energy is dissipated in the heater only when the specimen temperature is lower than the reference temperature. The maximal temperature for warming processes is set by a limiting diode in the integrator, whereas the minimal temperature for cooling processes is determined by the refrigerant temperature.

Speedtronic®---Tomorrow's Analog and Digital Gas Turbine Control System

This paper describes General Electric's new solid-state analog and digital gas turbine control, protection, and sequential system. It outlines the functional objectives and elaborates on the design philosophy applied to obtain maximum starting and running reliability, while maintaining a very high degree of fail safeness for the prime mover. It shows in graph and diagrammatic form the basic functions to be performed and schematically how these functions are accomplished. It describes and shows the physical arrangement of the system. The qualification program and operating experience to date are outlined.

The Application of an On-Line Digital Computer to the Control System of the High Flux Isotope Reactor (HFIR)

A process control computer was combined with the analog control system of the HFIR to perform the function of limiting the shim-rod reactivity additions as well as direct shim-rod symmetry control. Automatic shim control is supervised by a computer program which uses the measured reactor power level to continuously compute the core reactivity requirements during the 23-day fuel cycle. The high power density (4 Mw/liter) in the HFIR requires that flux tilting be controlled to minimize the possibility of hot-spot formation. This is accomplished by limiting the difference in shim-rod positions for reactor operation above 10 Mw. The rod symmetry is controlled by a computer program that actuates rod control relays in the analog system in response to the asymmetry determined from shim-rod position sensors. The rod control algorithm was tested on-line at 10 Mw, and routine operation of the on-line programs is planned after the overall reliability of the system has been measured.

A simple control method of beam transport system

A simple analogue control system for a beam transport system is proposed. Using a combination of a simultaneous current control system and slit stabilizers, the magnetic fields of several magnets can be simultaneously controlled with only manual control of one potentiometer. This control system was applied to the beam transport system of the tandem laboratory in Kyoto University and is being used successfully. A simple switching method of beam courses in a switching magnet is also presented.

Counter control system for high-energy experiments

An analog and time control system for a great number of counters is presented in which light diodes are used. The main feature of the system is that the light source attached to the counters are fired by only one pulse generator, with the time relations simulated to resemble high-energy particle passages. On-line analog control is effected by pulse height analysis of the photomultiplier output.

Using a Computer for the Design of Analog and Digital Control Systems

The paper illustrates the use of an analog computer to aid in the design of a feedback control system by building a working model on which performance measurements can be made. The model is made to duplicate more closely the physical control system by use of the computer in combination with actual production hardware. The particular system described is a digital speed regulated dc motor drive using a 3-phase full wave control silicon controlled rectifier armature supply.

A Model of Learning Mechanisms in the Brain

Publisher Summary In order to construct models of neural networks in which there is interaction between the neurons, it is necessary to define the model of synaptic transmission. The model proposed by Taylor is reproduced in this chapter. Permanent learning is only possible in networks that contain synapses with this type of characteristic for which the synaptic transmission, defined as the change in output firing rate produced by unit change in input firing rate, is changed by activity. It has recently been shown that the magnitude of the change in transmission required for learning behavior need only be a very small percentage of the initial or “birth” value. A restriction of the magnitude of the synaptic transmission is obviously required if a neuron with thousands of synapses is not to be overdriven, when a large percentage of excitatory synaptic endings are bombarded almost simultaneously at moderate impulse frequencies. Since an overdriven neuron ceases to produce impulses it represents a serious loss of information. If it is accepted that this is to be avoided, so far as possible there must be restrictions on the maximum resultant stimulation that a neuron can receive. The word resultant is important here since stimulation can be excitatory or inhibitory, or positive and negative. Thus, an excitatory stimulus many times the value required to drive a neuron at its maximum frequency could be almost exactly balanced by an inhibitory stimulus. The probability of this state existing by chance is extremely low, however, and it seems more feasible that it could only be maintained by negative feedback circuits. It is known that negative feedback plays an important role in the position control systems of the spinal cord and there is increasing evidence that the feedback principle is also employed throughout the brain. Analogue computers and control systems also make considerable use of the negative feedback principle and it is in these systems that the closest analogues of many neural circuits are to be found.

Application of Capacitors in Low Frequency and Long Time Constant Circuits

This paper discusses the low frequency (less than 1 cps) and long time constant applications and testing of capacitors as used in analog control systems. Emphasis is placed on tantalum electrolyric types, as they provide the necessary volume efficiency for airborne systems. The effective capacitance is always larger at the low frequencies than at normal capacitance bridge measuring frequencies. The amount and predictability of the change varies with the rate of charge, the dielectric material and, in the case of tantalums, with the electrolytic system. The polar characteristics of tantalum capacitors introduce other problems, such as doubling the effective capacitance during the first cycle of applied voltage, and hybrid charging curves as voltage levels change. The cause of the increase in charge or discharge time with low rates of change applied is not known. It is apparently allied with the characteristic of dielectric absorption (voltage recovery after shorting the electrodes) in that those capacitors exhibiting the least dielectric absorption also show the least low-frequency sensitivitye Polarization of molecules or molecular chains in the dielectric and/or electrolyte is the probable cause.