Modern computers and electronic instrumentation demand relatively stable AC input power in order to operate dependably. The power supplied by the utility companies is usually not adequate in this regard for sophisticated electronic applications. Typical problems are overvoltage and undervoltage transients, brown-outs and short term drop-outs. There are many different types of line regulators available to correct for those power line problems. The most advanced regulator systems are known as uninterruptable power systems, and the cost of these systems is sometimes larger than the equipment being regulated.
The systems designer is faced with the problem of determining the power line conditions and problems that prevail at an installation site in order to select a suitable regulator system. There is almost no instrumentation available to make meaningful line voltage measurements when many systems cannot even tolerate line transients of as short as one half cycle duration. Low cost meters use an averaging measurement technique that requires several cycles for a measurement. So since the designer has no equipment to measure the fast line transients, his only choice is to try various types of regulators until he finds a system that works for his application. This is most frustrating exercise, it is very costly and time consuming, and very often an expensive uninterruptable power system is specified because there was no instrumentation to measure the transients in the AC power in the power line.
The most common line voltage monitors are averaging types with slow responding, galvanometer strip chart recorders. These recorder systems are often useless for this purpose since they cannot respond to half cycle or one cycle transients. The half cycle transients are the most important parameters which the systems designer must know.
The most practical and meaningful measurement technique for AC voltages with large amounts of noise and distortion (typical AC line voltage) is the integrating technique. There are many solid state, integrated circuits available for voltage controlled oscillators, integrating voltage-to-frequency converters and similar circuits. These devices are designed for DC-controlled feedback loops, phase-locked loops and similar applications where only a limited control range is required, and where absolute accuracy is not of prime importance.
Therefore, a measurement system is needed which is capable of analyzing each half cycle of an AC voltage, and that can process accurately each measurement and record, or store in memory the worst case conditions over an extended period of time.