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Sunday, 3 February 2019

Signal Conditioners in Instrumentation

The term signal generator refers to the test instruments which generate for signal voltages of different waveforms required for testing the wide range of electronic equipment. They can be working in the audio frequency range, radio frequency range, or at any required frequency range. The signal generators may produce sinusoidal voltage, triangular voltage, square waves, ramp voltages, amplitude modulated signal, frequency modulated signal or pulse modulated signal. The type of signal produced and its magnitude depends on the application and design standards required for the particular application.

In general generating instruments are basically oscillators. An oscillator is a generator of AC waves. It can also be called as converter of DC energy to AC energy. Whatever may be the type of the oscillator it has to offer the following:

1. The frequency must be independent of the load impedance.
2. The frequency must be reasonably stable.
3. It must be free from short time drifts in frequency.
4. It should present a good wave shape.
5. The basic oscillator must be isolated from the rest of the circuit.

The current trend of generating instruments is to provide a digital splay of the output frequency. Mostly in the audio and high audio range we are provided with function generators as they provide not only the sinusoidal waveforms but also the other waveforms. The name world class instrument is always seen in the field. More facilities for example the output indication, auto selection of range portability are some of the features of these new series of generating instruments.

The waveform of a signal will be generally observed over the screen of a cathode ray oscilloscope. This CRT display uses time as the X-axis. The signal amplitude is shown against the time axis. That is we get a visual representation of the amplitude of the signal versus the time. This is the time domain.

The signal information can also be displayed in the frequency domain. An instrument that displays the signal information in the frequency domain is called a spectrum analyzer.

A logic analyzer provides a means of observing the number of digital signals simultaneously while it stores them in its memory. It is a multichannel oscilloscope.

(a) Audio Signal Generators:

These are called audio oscillators. They are meant for work from around 10 Hz to 20 kHz. However some audio oscillators can produce signals up to several tens of mega hertz. They produce sinusoidal output voltages. Some may be provided with a provision to get square wave output also.

(b) Function Generators:

These are also called the sweep function generators. They produce non sinusoidal signals and asymmetrical signals. These signals can be mathematically described as a function of time. Therefore they are called function generators. Triangular, ramp, square rectangular, and also sine wave voltages can be obtained from these function generators. They work in the frequency range from 0.001 Hz to around 20 MHz.

(c) AM Signal Generators :

These are generators that produce a sinusoidal signal in the radio frequency range. An audio signal of a single frequency or two frequencies (one at a time) are amplitude modulated over this RF signal. The resulting amplitude modulated signal will be given out as the output of the signal generator. Such signal generators can be of general purpose type or standard laboratory type. The frequency range of these AM signal generators ranges from 100 kHz to around 80 MHz.

(d) The AM/FM Signal Generators :

These are similar in many respects to the AM signal generator. The difference is that the frequency range of the oscillator is extended to the FM band of 88 MHz to 108 MHz. This frequency range is provided with frequency modulation of the carrier with the audio signal producing the required modulation index. They may also be provided with FM stereo facility. The higher frequency limit can be as large as 520 MHz.

(e) Pulse Generators :

A pulse generator generates the required pulses with the parameters of the pulse to our specifications. That is we have a facility to adjust the parameters of the pulse. Their frequency range extends from the audio frequency range to around tens of mega hertz. Though function generators produce pulses, pulse generators are exclusively meant for generating pulses of required parameters.

(f) Programmable Function Generators :

These combine signal generators and microprocessors to produce high quality complex signals using the frequency synthesizer. Use of microprocessor control enables the function generator compatible with automated control monitoring and system analysis.

(g) Random Noise Generators:

These are noise generators. They produce noise of known magnitude for use in the design of amplifiers, filters, in R.F. and microwave communication system.

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