MODULE V WAVE ANALYZERS G Anitha Asst Professor

MODULE V WAVE ANALYZERS G. Anitha Asst. Professor (Senior Grade) B S A Crescent Institute of Science and Technology

INTRODUCTION A wave analyzer is an instrument designed to measure relative amplitudes of single frequency components in a complex waveform. Basically, a wave instrument acts as a frequency selective voltmeter which is tuned to the frequency of one signal while rejecting all other signal components.

BASIC WAVE ANALYZER Basic wave analyzer mainly consists of three blocks − the primary detector, full wave rectifier, and PMMC galvanometer

BASIC WAVE ANALYZER Primary Detector − It consists of an LC circuit. We can adjust the values of inductor, L and capacitor, C in such a way that it allows only the desired harmonic frequency component that is to be measured. Full Wave Rectifier − It converts the AC input into a DC output. PMMC Galvanometer − It shows the peak value of the signal, which is obtained at the output of Full wave rectifier.

CIRCUIT DIAGRAM OF BASIC WAVE ANALYZER This basic wave analyzer can be used for analyzing each and every harmonic frequency component of a periodic signal

TYPES Frequency Selective Wave Analyzer Heterodyne wave analyzer

FREQUENCY SELECTIVE WAVE ANALYZER The wave analyzer, used for analyzing the signals are of AF range is called frequency selective wave analyzer

FUNCTION OF FREQUENCY SELECTIVE WAVE ANALYZER Input Attenuator − The AF signal, which is to be analyzed is applied to input attenuator. If the signal amplitude is too large, then it can be attenuated by input attenuator. Driver Amplifier − It amplifies the received signal whenever necessary. High Q-filter − It is used to select the desired frequency and reject unwanted frequencies. It consists of two RC sections and two filter amplifiers & all these are cascaded with each other. We can vary the capacitance values for changing the range of frequencies in powers of 10. Similarly, we can vary the resistance values in order to change the frequency within a selected range. Meter Range Attenuator − It gets the selected AF signal as an input & produces an attenuated output, whenever required. Output Amplifier − It amplifies the selected AF signal if necessary. Output Buffer − It is used to provide the selected AF signal to output devices. Meter Circuit − It displays the reading of selected AF signal. We can choose the meter reading in volt range or decibel range.

SUPER HETERODYNE WAVE ANALYZER The wave analyzer, used to analyze the signals of RF range is called superheterodyne wave analyzer

FUNCTION OF SUPER HETERODYNE WAVE ANALYZER The RF signal, which is to be analyzed is applied to the input attenuator. If the signal amplitude is too large, then it can be attenuated by input attenuator. Untuned amplifier amplifies the RF signal whenever necessary and it is applied to first mixer. The frequency ranges of RF signal & output of Local oscillator are 0 18 MHz & 30 48 MHz respectively. So, first mixer produces an output, which has frequency of 30 MHz. This is the difference of frequencies of the two signals that are applied to it. IF amplifier amplifies the Intermediate Frequency (IF) signal, i. e. the output of first mixer. The amplified IF signal is applied to second mixer. The frequencies of amplified IF signal & output of Crystal oscillator are same and equal to 30 MHz. So, the second mixer produces an output, which has frequency of 0 Hz. This is the difference of frequencies of the two signals that are applied to it. The cut off frequency of Active Low Pass Filter (LPF) is chosen as 1500 Hz. Hence, this filter allows the output signal of second mixer. Meter Circuit displays the reading of RF signal. We can choose the meter reading in volt range or decibel range.

APPLICATIONS OF WAVE ANALYZERS Wave analyzers have very important applications in the following fields Electrical Measurements Sound measurements Vibration measurements

HARMONIC DISTORTION ANALYZERS Applying a sinusoidal signal to the input of an ideal linear amplifier will produce a sinusoidal output waveform. However, in most cases the output waveform is not an exact replica of the input signal because of various types of distortion.

DISTORTION ANALYZERS The extent to which the output waveform of an amplifier differs from the waveform at the input is a measure of the distortion intro duced by the inherent nonlinear characteristics of active devices such as bipolar or field effect transistors or by passive circuit components. The amount of distortion can be measured with a distortion analyzer.

DISTORTION ANALYZERS When an amplifier is not operating in a linear fashion, the output signal will be distorted. Distortion caused by nonlinear operation is called amplitude distortion or harmonic distortion. It can be shown mathematically that an amplitude distorted sine wave is made up of pure sine wave components including the fundamental frequency f of the input signal and harmonic multiples of the fundamental frequency, 2 f, 3 f, 4 f. . . , and so on.

DISTORTION ANALYZERS When harmonics are present in considerable amount, their presence can be ob served with an oscilloscope. The waveform displayed will either have unequal positive and negative peak values or will exhibit a change in shape. In either case, the oscilloscope will provide a qualitative check of harmonic distortion. However. the distortion must be fairly severe (around 10%) to be noted by an untrained observer.

DISTORTION ANALYZERS In addition, most testing situations require a better quantitative measure of harmonic distortion. Harmonic distortion can be quantitatively measured very accurately with a harmonic distortion analyzer, which is generally referred to simply as a distortion analyzer.

DISTORTION ANALYZERS A block diagram for a fundamental suppression harmonic analyzer is shown in Fig. 1. When the instrument is used. switch S, is set to the "set level" position, the band pass filter is adjusted to the fundamental frequency and the attenuator network is adjusted to obtain a full scale voltmeter reading. Fig. 1 Block diagram of a distortion analyzer.

DISTORTION ANALYZERS Switch S, is then set to the "distortion" position, the rejection f: 1 ter is turned to the fundamental frequency, and the attenuator is adjusted for a maximum reading on the voltmeter.

DISTORTION ANALYZERS The total harmonic distortion (THD). which is frequently expressed as a percentage, is defined as the ratio of the rms value of all the harmonics to the rms value of the fundamental, or

DISTORTION ANALYZERS This defining equation is somewhat inconvenient from the standpoint of measurement. An alternative working equation expresses total harmonic distortion as the ratio of the rms value of all the harmonics to the rms value of the total signal including distortion. That is,

DISTORTION ANALYZERS On the basis of the assumption that any distortion caused by the components within the analyzer itself or by the oscillator signal are small enough to be neglected. Eq. 2 can be expressed as where THD = the total harmonic distortion Ef = the amplitude of the fundamental frequency including the harmonics E 2 E 3 En = the amplitude of the individual harmonics THD = E(harmonics) fundamental

DISTORTION ANALYZERS EXAMPLE 1: Compute the total harmonic distortion of a signal that contains a fundamen tal signal with an rms value of 10 V, a second harmonic with an rms value of 3 V, a third harmonic with an rms value of 1. 5 V, and a fourth harmonic with an rms value of 0. 6 V.

DISTORTION ANALYZERS SOLUTION: Using Eq. 3, we compute the total harmonic distortion as

HARMONIC DISTORTION ANALYZERS Fig. 2 a and Fig 2 b

HARMONIC DISTORTION ANALYZERS Fig 2 a is a harmonic distortion analyzer used to measure THD. The signal source has very low distortion and this can be checked by reading its output distortion by connecting directly in to the analyzer The signal from the source is fed in to the amplifier under test. This generayes harmonics and the original fundamental frequency. The fundamental frequency is removed by the notch filter

HARMONIC DISTORTION ANALYZERS The switch SW is first placed in position 1 and the total content of fundamental and harmonics is measured. Then the switch is moved to position 2 to measure just the harmonics. The value of THD is THD= EH/ET*100

HARMONIC DISTORTION ANALYZERS Fig. 2 b shows an alternative arrangement, where the values of Et and Eh are read simultaneously and their ratio calculated and displayed as THD on the indicator. For good accuracy the notch filter must have excellent rejection and high pass characteristics

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