Electronic measuring instruments
The electronic instrument used to analyze waves is called a wave analyzer . It is also called a signal analyzer because the terms signal and wave can be used frequently interchangeably.
We can represent the periodic signal as the sum of the following two terms.
- DC component
- Series of sinusoidal harmonics
Thus, the analysis of A periodic signal is the analysis of the harmonic components present in it.
Base wave analyzer
The base wave analyzer mainly consists of three blocks - the primary detector, the full wave rectifier and the PMMC galvanometer . The block diagram of the basic wave analyzer is shown in the figure below -
The function of each block present in the Basic wave analyzer is mentioned below.
Detectorr primary - It consists of an LC circuit. We can adjust the values of inductance, L and capacitor, C in such a way that it allows only the desired harmonic frequency component to be measured.
Complete Wave Rectifier - It converts AC input to DC output.
PMMC Galvanometer - It shows the peak value of the signal, which is obtained at the output of the full wave rectifier.
We will get the corresponding circuit diagram, simply by replacing each block with the respective component (s) in the above diagram of the wave analyzer. based. So the electrical diagram of the basic wave analyzer will look like the one shown in the following figure -
This basic wave analyzer can be used to analyze each harmonic frequency component of a periodic signal.
Types of Wav e Analyzers
Wav e Analyzers 'waves can be classified into the following two types .
- Frequency selective wave analyzer
- Superheterodyne wave analyzer
Let's talk now of these two wave analyzers one by one.
Frequency selective wave analyzer
The wave analyzer, used to analyze the signals are of range AF, is called selective wave analyzer in frequency. The block diagram of the frequency selective wave analyzer is shown in the figure below.
The frequency selective wave analyzer consists of a set of blocks. The function of each block is mentioned below .
Input attenuator - The AF signal, which is to be analyzed is applied to the input attenuator. If the signal amplitude is too large, it can be attenuated by the input attenuator.
Driver Amplifier - It amplifies the received signal whenever necessary.
High Q filter - It is used forr select the desired frequency and reject unwanted frequencies. It consists of two RC sections and two filter amplifiers and all of these are cascaded with each other. We can vary the capacitance values to change the frequency range to powers of 10. Likewise, 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 input and produces attenuated output, whenever needed.
Output amplifier - It amplifies the selected AF signal if necessary.
Output Buffer - It is used to supply the selected AF signal to the output devices.
Measuring circuit - It displays the reading of the selected AF signal. We can choose the meter reading in volt range or in dec range.ibels.
Superheterodyne W wave analyzer
The wave analyzer, used to analyze signals of the RF range is called analyzer superheterodyne wave. The following figure shows the block diagram of the superheterodyne wave analyzer.
The operation of the analyzer The superheterodyne wave is mentioned below.
The RF signal to be analyzed is applied to the input attenuator. The signal amplitude is too large, then it can be attenuated by input attenuator .
The amplifier not tuned amplifies the RF signal whenever needed and it is applied to the first mixer.
The frequency ranges of the RF signal and the output of the local oscillator are 0-18 MHz and 30-48 MHz respectively. Thus, the first mixer produces an output, which has a frequency of 30 MHz. This is the difference in frequencies of the two signals which are applied to himqués.
The IF amplifier amplifies the intermediate frequency (IF) signal, i.e. the signal output from the first mixer . The amplified IF signal is applied to the second mixer.
The frequencies of the amplified IF signal and the output of the Crystal oscillator are the same and equal to 30 MHz. So the second mixer produces an output, which has a frequency of 0 Hz. This is the difference in frequencies of the two signals applied to it.
The cutoff frequency of the Active Low Pass Filter (LPF) is chosen as 1500 Hz. Therefore, this filter allows the output signal of the second mixer.
Meter Circuit displays the RF signal reading. We can choose the meter reading in the volt range or the decibel range.
Thus, we can choose a particular wave analyzer according to the frequency range of the signal to analyzeser.