Electrical Test Equipment

Type of physical science: Classical physics

Field of study: Electromagnetism

Electrical circuitry is often technically complex and subject to any number of conditions that might impact the way it functions. Electrical test equipment is employed to measure the conductive properties of the materials used in that circuitry and to isolate problems. This equipment is often highly sophisticated, capable of providing an efficient measure of circuit performance.

Overview

In order to ensure the integrity of its electronic circuitry, design and maintenance engineers must be able to analyze the performance of every component in an electronic system.

While the designer's schematics may provide an accurate blueprint of the final product, that representation is of little value to the engineer who must service the product when it needs repair.

Electrical test equipment is used to help locate and characterize problems in ways that suggest what should be done to correct them.

There are two kinds of electrical test equipment: general-purpose and special-purpose.

General-purpose test equipment is versatile, performing a variety of tests over a wide range of electronic systems. Included are signal generators, oscilloscopes, tube testers, and multimeters, among others, each capable of performing a different set of diagnostic observations of conditions as they exist in an electronic circuit. Special-purpose test equipment is used in specific areas of electronics, such as radar, broadcasting, and space science, where the special demands of extraterrestrial operation require unique electrical circuit designs. Included are field intensity meters, spectrum analyzers, and radar test sets.

The multimeter is able to measure the number of volts, amperes, and ohms present in an electrical circuit and do so more accurately than a voltmeter, ammeter, or ohmmeter in their nonelectronic form. The ammeter and ohmmeter components of the multimeter are similar to their nonelectronic counterparts, but the voltmeter component includes an electron tube not found in its nonelectronic counterpart. The electronic tube gives the voltmeter a much greater sensitivity to the level of current moving along a circuit, so that an accurate reading can be achieved without loading down the test unit. Additionally, the standard voltmeter is virtually useless as a way to measure voltage in high-impedence circuits.

Tube testers are used to determine whether electron tubes are conducting current according to specifications. Such tubes are self-contained electrical components that can be replaced when they become defective. During the early days of radio and television, most receiving sets contained a number of replaceable tubes, and tube testers were often found in common drugstores and other high-traffic areas, allowing consumers to check tubes and purchase replacements. Eventually, most tubes were replaced by transistors. Newer sets are no longer serviceable except by professional technicians.

Transistor test sets are designed to measure the amount of current flowing through a transistor while it is connected to a circuit and when it is disconnected from the circuit.

Transistors work much the same as electron tubes. They perform the same functions but differ in that they are much more efficient, compact, and capable of withstanding abuse. By measuring the flow of current through the transistor when it is inside and when it is outside the circuit, technicians can determine whether a transistor is performing up to specifications or whether a problem might lie elsewhere in the circuit.

Oscilloscopes are used to observe the frequency swing of voltage. Voltage can be observed graphically on a fluorescent cathode-ray screen in the form of a frequency signal, a useful way to study its character. Oscilloscopes are especially useful in the analysis of the voltage characteristics of video equipment.

Frequency measuring equipment is used to determine and maintain radio frequencies or oscillation frequencies necessary for the operation of some kinds of electronic equipment. All frequency measuring equipment is calibrated to one of two frequency standards: primary or secondary. Primary frequency standards are set by the U.S. Bureau of Standards according to a standard interval of time, while secondary standards are calibrated against primary standards for the purpose of doing highly accurate readings of frequency levels in highly specialized equipment. Secondary frequency standards are used in equipment that includes divider stages capable of measuring and generating harmonics.

Sometimes it is useful to test the relative strength of electronic equipment designed to broadcast radio signals. Examples are radio and television transmitters used by broadcasters, businesses, municipalities, public services, air traffic controllers, and cellular service providers, among others. Field test equipment includes field-intensity meters that measure the strength of those signals at various distances from the transmission point. This is useful in helping determine whether a broadcast station is meeting the output requirements specified in its license or finding the source of undesirable signals that may be causing interference. It is also useful in setting up directional antenna arrays as a tool for plotting pattern configurations.

Spectrum analyzers are used to visualize radio waves that are amplitude-modulated, such as those used in radar and some forms of broadcasting. The on-screen presentation shows a graph of voltage versus frequency. Spectrum analysis is yet another useful way of looking at a modulated signal in order to study its characteristics.

Applications

Most electronic circuitry is extremely sophisticated, composed of hundreds, thousands, even millions of components. The only way to design, operate, and maintain such systems is to have the equipment necessary to observe the performance of each component before and during operation. Test equipment has been devised over the years to support the evolution of all kinds of systems, from military communications to consumer electronics.

General-purpose test equipment is designed to measure values common to all electrical systems. Meters are used to display those values at strategic points within a circuit, but when a breakdown occurs along the way or there is a need to monitor or recalibrate, test equipment is used to measure voltage, resistance, amperage, frequency, and other values. Electrical test equipment is used to gauge the efficiency of electrical transmission facilities and telecommunications networks by checking actual performance of those facilities--cable, wire, switches, transformers--against standard specifications for each component. Once those facilities reach the customer's location, test equipment is used to evaluate performance of the equipment at the customer's premises so that problems can be identified and corrected.

Consumer electronics often require service of individual components that fail as a result of manufacturer's defects, excessive wear, mishandling, or poor maintenance. When that occurs, test equipment is used to locate short circuits and other problems that might be remedied by simply replacing a connector plug or wire. When more involved service is required, professional technicians use test equipment to analyze internal circuitry. Diagnostic equipment is being used increasingly in the automobile service industry as automobile engines begin to rely more and more heavily on electronic ignition and other electrical systems. Also, the burgeoning computer industry has created a whole new variety of specialized test equipment designed to ferret out problems in the extremely small components found in modern computer systems.

Often, electrical equipment must be monitored constantly and recalibrated to function properly. An example is radar, which can deteriorate by as much as 10 decibels while being operated, without the operator's knowledge. Internal diagnostics have been designed to test systems constantly while they are in use and, in some cases, make automatic adjustments. Radar installations use a device known as an echo box that captures a radar oscillation and causes it to persist after the pulse has ceased. The time it takes the oscillation to decay to some negligible value is a measure of the efficiency of the unit. Such tests are extremely important in radar where the function of systems is to reflect objects at various distances from the point of origin of radar pulses. Should the decibel level of the pulses vary significantly during operation, the relative distance of objects from the radar transmitter might be misrepresented significantly, thereby compromising the efficiency of the system. Despite the significant advancement radar has gained from the wide availability of portable computer-driven components that can adjust instantly for changing conditions, radar electronics is extremely dependent upon diagnostics.

One of the fastest-growing industries in this information age is that of telecommunications. Vast new global networks designed to transmit voice and data information are being deployed to meet an ever-increasing demand for instantaneous communication links worldwide. These networks incorporate wire, optical fiber, satellites, microwave relays, cellular telephones, broadcast transmitters, and scores of other technologies, each of which must operate according to standards designed to make the telecommunication environment as user friendly as possible. All these technologies are electronic and require legions of technicians armed with test equipment to ensure that they operate at maximum efficiency.

Context

Over the past two centuries, industrial technology has become increasingly reliant upon electricity. Perhaps its greatest attraction is that electric power can be created in many different ways, often using renewable natural resources like water power and solar. That keeps costs down and provides an incentive to manufacturers to continue designing and building products that require electricity to operate. In short, electric power as a source of energy is here to stay, while other nonrenewable sources of energy are threatened by dwindling reserves. In the future, virtually all energy required to propel the engine of human endeavor may well be transformed into electricity before being tapped at the production end.

On the other hand, electricity must travel along a sophisticated network of finely tuned substances and materials that are continuously subjected to a multitude of conditions that may alter their character, perhaps causing them to fail. Where it was once a fairly simple task to locate and correct problems within any electronic circuit, advancements in manufacturing techniques now make it possible to place extraordinarily complex electronic systems on very small platforms called microchips. New kinds of test equipment have been devised to determine whether such chips are functioning optimally, and in this new microelectronic environment, defective chips are often discarded and replaced rather than serviced, much the way electron tubes were in the pretransistor era. Therefore, the technology employed in the design of this new test equipment must also continue to evolve.

Perhaps no industry has had as much impact on society as has broadcasting over the past century. Thousands of radio and television stations continuously broadcast a wide variety of entertainment and information programming to almost every home over the "airwaves," the electromagnetic spectrum. Each station must be assigned a specific and finite amount of spectrum space in which to operate in order to avoid chaos across that spectrum. Government agencies must then enforce adherence to the technical parameters assigned to each using a variety of techniques that rely heavily on their ability to monitor the technical operation of these stations.

In the future, similar technologies will be used to provide mass media programming, and the demand for test equipment will continue to grow.

New metal alloys are being developed for use in highly sophisticated applications such as space electronics. Such equipment must be designed to function normally, despite the often unpredictable effects of the outer space environment, with its exotic magnetic properties, cosmic radiation, and temperature variations. Even terrestrial communications systems are increasingly designed to operate in concert with space-based platforms called satellites. Satellite systems receive and transmit signals over a wide area of the earth's surface. New techniques are being employed to diagnose problems in space-based equipment. The remoteness of that equipment often precludes servicing it, despite the fact that the costs of deploying such technology is extremely high. Test equipment must be extremely accurate, dependable, and versatile.

Electrical system designers will continue to rely heavily on equipment that can check and monitor the performance of each component in a system. Scientists will continue to develop new technology.

Principal terms

FIELD INTENSITY METER: a portable receiver that includes a meter to indicate the strength of an incoming broadcast signal

GENERAL-PURPOSE TEST EQUIPMENT: equipment designed to perform analysis on a wide variety of electrical devices, circuits, and systems

MULTIMETER: a device that combines a voltmeter, ohmmeter, and ammeter in one portable tool used to test a variety of electronic equipment

OSCILLOSCOPE: a device that includes a cathode-ray tube, sweep generator, horizontal deflection amplifier, and vertical deflection amplifier; used to observe voltage waveforms in electrical circuits

SIGNAL GENERATOR: a device that includes audio and video generation units that produce stable frequency signals used to test audio and video circuits

SPECIAL-PURPOSE TEST EQUIPMENT: equipment designed to perform analysis on a specific type of electronic device or circuit

SPECTRUM ANALYZER: a device that provides a visual observation of the frequency component of an AM radio wave; used to study radio frequency spectrum produced when a carrier signal is modulated

TRANSISTOR TESTER: a device that includes a reference oscillator, tuned amplifier, and variable bias supply that together in one test set are used to check transistors for internal short circuits and overall performance

TUBE TESTER: a device that measures the conductance of electron tubes used in radio receivers and transmitters and other electronic equipment

Bibliography

Albert, Arthur Lemuel. ELECTRONICS AND ELECTRON DEVICES. New York: Macmillan, 1956. This volume contains a lucid and comprehensible discussion of basic electronic theory. Other areas discussed are amplifiers, rectifiers, oscillators, semiconductors, and photoelectric devices. Contains illustrations, diagrams, and an index.

Bureau of Naval Personnel. BASIC ELECTRONICS. Washington, D.C.: U.S. Bureau of Naval Personnel, Navy Training Course, 1968. This volume contains a good discussion of antennas, receivers, and an introduction to computers and their electronics. Includes a very thorough discussion of electrical test equipment. Contains an excellent glossary of electrical terminology. A good introduction to electronics.

Lurch, E. Norman. FUNDAMENTALS OF ELECTRONICS. New York: John Wiley & Sons, 1981. In addition to a good discussion of fundamental electronic principles, this volume contains an excellent in-depth discussion of the concept of amplification in electronic circuitry. Contains diagrams, illustrations, and an index.

Mullin, William F. ABC'S OF CAPACITORS. New York: Howard W. Sams, 1976. While this article does not address electrical test equipment specifically, electronic circuitry cannot function without capacitors, and it is useful to understand the fundamental principles of capacitance to understand how electrical systems are able to function. Contains diagrams and an index.

Turner, Rufus B. ABC'S OF RESISTANCE AND RESISTORS. New York: Howard W. Sams, 1974. This thin volume offers a good introduction to the topic of resistance, conductivity, and electrical system design, stressing the fundamental concepts of electricity and differentiating among the several types of resistance and resistors. Contains diagrams and an index.

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