Introduction to instruments

Recommended questions:

1. 
   Explain why time delay is necessary in oscilloscopes?
   
2. 
   Sketch and explain the block diagram of delayed time base oscilloscope.
   
3. 
   Explain with the help of waveforms, how a portion to be studied is brightened in delayed time base oscilloscope.
   
4. 
   Describe the following storage techniques used in storage oscilloscopes:[jun 09]
   
   1. 
      Mesh storage ii)Phosphor storage
      
5. 
   Compare the mesh and phosphor storage techniques.
   
6. 
   Draw and explain the block diagram of digital storage oscilloscope.[jul 07]
   
7. 
   State the advantages of sampling oscilloscope
   
8. 
   Explain the expanded mode operation of sampling oscilloscope
   
9. 
   Explain the special function which can be performed by digital storage oscilloscope.
   
10. 
    Explain the applications of digital storage oscil/oscope.[jul 08]
    

Unit:V Hrs: 06

Syllabus:
Signal Generators

Introduction, Fixed and variable AF oscillator, Standard signal generator, Laboratory type signal generator, AF sine and Square wave generator, Function generator, Square and Pulse generator, Sweep frequency generator, Frequency synthesizer (Text 1: 8.1 to 8.9 &Text 2: 11.5, 11.6 )

Recommended readings:

1. 
   “Electronic Instrumentation”, H. S. Kalsi, TMH, 2004
   
2. 
   “Electronic Instrumentation and Measurements”, David A Bell, PHI / Pearson Education, 2006.
   

UNIT III

SIGNAL GENERATORS

Introduction:

Signal generator provides variety of different signals for testing various electronic circuits at low powers. The signal generator is an instrument which provides several different output waveforms including sine wave, square wave, triangular wave, pulse train and an amplitude modulated waveform.

Requirements of Laboratory Type Signal Generator:

There are different types of signal generator. But the requirements are common to all the types.

1. 
   The output frequency of signal generator should be very stable .
   
2. 
   The amplitude of output signal of signal generator should be controllable from low values to relatively large values.
   
3. 
   The amplitude of output signal must be stable. the harmonic contents in the output should be as low as possible. The output signal should be distortion free.
   

v) The signal generator should provide very low spurious output; that means effect of hum, noise, jitter and modulation should be negligible.

A F oscillator:

The signal generators which provide sinusoidal waveforms in the frequency range of 20 Hz to 20 kHz are called audio frequency(A.F.) signal generator. Depending upon the load, in modern AF signal generators a provision is made to select output impedance either 50 n or 600 n. To generate audio frequency signals, in practice RC feedback oscillators are used. The most commonly used RC feedback oscillators are Wien Bridge oscillator and RC phase shift oscillator. Let us discuss both the types of oscillators in detail.

Wien Bridge Oscillator using Op-amp:

The Fig shows the Wien bridge oscillator using an op-amp.


nle resistance R and capacitor C are the components of frequency sensitive arms of the bridge. The resistance Rf and R1 form the part of the feedback path. The gain of

noninverting op-amp can be adjusted using the resistance Rf and R1. The gain of op-amp is,

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