EI 1302 (2 MARKS) UNIT III

Unit III

1. Name the components of a time domain oscilloscope?
The time domain oscilloscope contains the following component blocks,
o Display device
o vertical amplifier
o Time base
o Horizontal amplifier
o Trigger or sync circuit
o Gate amplifier
o Power supply

2. Describe about the classifications of oscilloscope?
Classification based on frequency
a)Low frequency oscilloscope
b)High frequency oscilloscope
c)Sampling Oscilloscope

Classification based on CRT used
a)Standard phosphor oscilloscope
b)storage oscilloscope.

3. Explain the classification of CRT?
According to the number of independent electron beams and tube the CRT is classified as:
a) single beam CRT
b) dual beam CRT
c) multi beam CRT
According to the deflection technique used:
a) electro magnetic CRT
b) electro static CRT
In electrostatic CRT again classifications can be made according to the design in deflection plates as:
a) parallel plate CRT
b) bent plate CRT
c) segmented plate CRT
d) distributed plate CRT
According to the acceleration given:
a) monoaccelerator CRT
b) postaccelerator CRT
According to the target decay characteristics:
a) standard CRT
b) storage CRT
c) variable persistence CRT

4. What is meant by Aluminising a CRT and explain its advantage?
Aluminizing a CRT is depositing a thin layer of aluminium on the non-viewed side of the phospher screen . it has 3 major functions,its original function was to build-up of charges on the phospher,which tends to slow down the electron and limit brightness.also aluminizing serves to reduce light scatter when beam hits the phosphor.with the aluminized layer,the light emitted back into the tube is reflected again towards the viewer and thus increases the brightness.the aluminium layer acts as a heat sink for the phospher and thus materially reduces the danger of phospher burning.

5. What is scan angle?
It is the number of screen divisions which can be scanned,fullscreen scan is often achieved before the beam intercepts the deflection plate itself.it is one of the significant parameter of electrostatic tube.

6. Describe about writing speed?
Photographic writing speed is a measure of the fastest deflection rate of a single beam trace that is just barely vivible on film,it is affected not only by CRT parameters such as density of beam current,accelerating voltage,and phospher , but also by parameters such as light filters,camera lenses and film speed and sensitivity.cathode-ray tube writing speed is typically given in centimeter/microsecond.

7. What are graticules?
Graticules are scale markings on or near the CRT screen to aid the user in display analysis by calibrating beam deflection. The number of scale divisions multiplied by the appropriate switch settings gives the amplitude difference and time duration between any two points on an observed waveform. Three kinds of graticule system are in use
o External Graticule
o Internal Graticule
o Projected Graticule

8. What is fading positive?
The stored pattern eventually degrades, primarily because ions generated by flood gun electrons charge other regions of the storage surface and the entire display consequently appears to be written. This is called fading positive.

9. Define the technique used in sampling oscilloscope?
Sampling device samples the signal amplitude at regulated intervals and synthetically reproduces the sampled signal. These signals are presented on the CRT as a series of dots.

10. State the prime advantage of peak responding voltmeter?
When no ac pre-amplification is required the rectifying diode and the storage capacitor may be taken out of the instrument and placed in the probe.

11. Define coherent and incoherent sampling?
If the input voltage is sampled at equal interval, this type of sampling is known as coherent sampling.It is primarily used when the waveform must be preserved for visual presentation or phase measurement
If the input voltage is sampled at irregular interval that have no relationship to any of the frequency components of the input signal, this type of sampling is known as in-coherent sampling. It is used in voltmeters due to meter sensitivity, accuracy and broad frequency range of a sampling instrument.

12. Define wave analyzer and name its type?
A wave analyzer is an instrument designed to measure the relative amplitudes of single frequency components in a complex or distorted waveform. The types of wave analyzer are
 Frequency selective wave analyzer
 Heterodyne wave analyzer

13. Name any two application of wave analyzer?
Fields of electrical measurement and sound
Vibration analysis

14. What are the drawbacks of tuned circuit harmonic analyzer?
The two major drawbacks are
 At low frequency very large values of L & C are required and their physical size becomes rather impractical
 Harmonics of the signal frequency are often very close in frequency so that it becomes extremely difficult to distinguish between them.

15. Name the major components of fundamental suppression harmonic distortion analyzer?
 Input circuit
 Impedence converter
 Rejection amplifier
 Metering circuit
 Power supply

16. Define the technique for noise generation?
The method for generating noise is to use a semiconductor noise diode which delivers frequencies in a band roughly extending from 80-220 KHz.

17.What are the important features of an instrumentation amplifier?
 Selectable gain with high gain accuracy and gain linearity
 Differential input capability with high gain common mode rejection
 High stability of gain with low temperature co-efficient
 Low DC offset anf drift errors referred to input
 Low output impedence

18. State the principle of Q-meter.
Principle of Q-meter is based on series resonance; the voltage drop across the coil is Q times the applied voltage
At resonance XL = XC and

EL= I XL ;

EC= I XC ;

E = I R

Q = X L / R = X C / R = EC / E

19. State the principle of Lock-in amplifier?
The lock in amplifier is basically a band pass filter amplifier that overcomes the Q limitations of conventional circuits.

20. Name the front panel controls used in signal generator?
 Frequency selector
 Frequency multiplier
 Amplitude multiplier
 Variable amplitude
 Symmetry control
 Amplitude
 Function Switch
 Output
 Sync
 On-Off Switch