Tag: AC Circuits

12.6 AC Instrumentation Transducers
Just as devices have been made to measure certain physical quantities and repeat that information in the form of DC electrical signals (thermocouples, strain gauges, pH probes, etc.), special devices have been made that do the same with AC. It is often necessary to be able to detect and transmit the physical position of mechanical…

12.5 AC Bridge Circuits
As we saw with DC measurement circuits, the circuit configuration known as a bridge can be a very useful way to measure unknown values of resistance. This is true with AC as well, and we can apply the very same principle to the accurate measurement of unknown impedances. How Does a Bridge Circuit Work? To review, the bridge circuit…

12.4 Power Quality Measurement
It used to be with large AC power systems that “power quality” was an unheardof concept, aside from power factor. Almost all loads were of the “linear” variety, meaning that they did not distort the shape of the voltage sine wave, or cause nonsinusoidal currents to flow in the circuit. This is not true anymore. Loads controlled…

12.3 Power Measurement
Power measurement in AC circuits can be quite a bit more complex than with DC circuits for the simple reason that phase shift complicates the matter beyond multiplying the voltage by current figures obtained with meters. What is needed is an instrument able to determine the product (multiplication) of instantaneous voltage and current. Fortunately, the…

12.2 Frequency and Phase Measurement
An important electrical quantity with no equivalent in DC circuits is frequency. Frequency measurement is very important in many applications of alternating current, especially in AC power systems designed to run efficiently at one frequency and one frequency only. If the AC is being generated by an electromechanical alternator, the frequency will be directly proportional to…

12.1 AC Voltmeters and Ammeters
AC electromechanical meter movements come in two basic arrangements: those based on DC movement designs, and those engineered specifically for AC use. Permanentmagnet moving coil (PMMC) meter movements will not work correctly if directly connected to alternating current, because the direction of needle movement will change with each halfcycle of the AC. (Figure below) Permanentmagnet meter movements,…

7.5 Circuit Effects
The principle of nonsinusoidal, repeating waveforms being equivalent to a series of sine waves at different frequencies is a fundamental property of waves in general and it has great practical import in the study of AC circuits. It means that any time we have a waveform that isn’t perfectly sinewaveshaped, the circuit in question will…

7.4 More on Spectrum Analysis
Computerized Fourier analysis, particularly in the form of the FFT algorithm, is a powerful tool for furthering our understanding of waveforms and their related spectral components. This same mathematical routine programmed into the SPICE simulator as the .fourier option is also programmed into a variety of electronic test instruments to perform realtime Fourier analysis on…

7.3 Other Waveshapes
As strange as it may seem, any repeating, nonsinusoidal waveform is actually equivalent to a series of sinusoidal waveforms of different amplitudes and frequencies added together. Square waves are a very common and wellunderstood case, but not the only one. Electronic power control devices such as transistors and siliconcontrolled rectifiers (SCRs) often produce voltage and…

7.2 Square Wave Signals
It has been found that any repeating, nonsinusoidal waveform can be equated to a combination of DC voltage, sine waves, and/or cosine waves (sine waves with a 90 degree phase shift) at various amplitudes and frequencies. This is true no matter how strange or convoluted the waveform in question may be. So long as it…

7.1 Introduction to MixedFrequency AC Signals
In our study of AC circuits thus far, we’ve explored circuits powered by a singlefrequency sine voltage waveform. In many applications of electronics, though, singlefrequency signals are the exception rather than the rule. Quite often we may encounter circuits where multiple frequencies of voltage coexist simultaneously. Also, circuit waveforms may be something other than sinewave…