Electrical Measurements and Instrumentation Lab Viva Questions
1. What you know about the Cathode ray oscilloscope (CRO)?
Basically the Cathode ray oscilloscope (CRO) is considered as the 'eye' of an electronics engineer. An electronics engineer can see all the signals and waveforms with the help of CRO. Initially it was known as Oscillograph. The use of CRO is for the measurement and analysis of waveforms, for display and other phenomenon in electrical and electronic circuit. CRO has 4 sections namely display, vertical controllers, horizontal controllers and triggers. Probes are used for input and output measurements in CRO. the waveform is plotted in CRO by plotting amplitude 'A' on x axis and time 't' on y-axis. The main applications of CRO are: Radio, TV Receivers, etc.
2. Discuss the need of aquadag in CRO?
The main use of aquadag in CRO is to collect the secondary electrons emitted from the inner tube surface of CRT.
3. Mention the advantages of an instrument transformer?
The main advantages of an instrument transformer are:
• Instrument transformer can be used for 5 A current & 100 to 200 V measurements and are moderate in size.
• The cost is very less.
• Easy replacements of damaged parts of the transformer
• Low power consumption
• Highly safe for use.
4. What you know about the sensitivity of a measurement?
The ratio of change in response (output) of the instrument to the change of measured variable (input).
Sensitivity of measurement = change in output (response) of the instrument/change of input or measured variable
5. Discuss in brief about instrument transformer?
For the measurement of electrical quantities like voltage, power factor, current, power and frequency, an instrument transformer is used. The main application of these types of transformers are in relays for protecting the power system.
6. List the classification of instrument transformers?
Instrument transformers are mainly classified into two types namely:
• Voltage transformer and
• Current transformers.
7. What you understand about the error of a measurement?
The difference between the actual value (true value) and the measured value is termed as the measurement error. It is also known as observational error.
Measurement Error = Actual value - Measured value
8. List the different types of probes used in CRO?
The different types of probes used in CRO are:
• Detector probe
• Isolation probe and
• Direct probe
9. What you know about the precision of a measurement?
If two or more values of the measurements are closed to each other, then it is termed as precision. In other words, precision can be defined as the successive readings does not differs. Due to observational error, the precision value diverges (differs). In order to find the consistency and reproducibility of the measurement, precision is used. The characteristics of precision are: the conformity and the number of significant figures.
10. Write down the equation of transformation ratio of instrument transformer?
Transformation ratio = (primary winding current of an instrument transformer)/(secondary winding current of an instrument transformer)
11. Discuss the use of electron-gun assembly in CRT?
In order to provide a focused electron beam, accelerated towards the phosphor screen, the electron gun assembly is used. The main parts of electron-gun assembly are: an indirectly heated cathode, a control grid surrounding the cathode and an anode (accelerating anode).
12. What are the three reasons for the instrumental error ?
The main reasons for instrumental error are:
a. Inherent shortcoming in the instrument
b. Loading effect of instrument
c. Misuse of the instruments
13. What you know about the resolution of a measurement?
The smallest change in measured variable for distinguishing different values so that an instrument responds is known as resolution of a measurement.
The accuracy of measurement and the specified resolution of an instrument has no relation.
14. Give the equation of Nominal ratio of instrument transformer?
The nominal ratio of instrument transformer can be obtained as:
Nominal ratio = (Rated primary winding current of an instrument transformer)/(The rated secondary winding current of an instrument transformer)
15. Discuss the use of a current transformer?
The main use of current transformers (CT) is to measure the current of a circuit. In order to monitor the high voltage lines across national power grids, current transformers are commonly used. The current transformer is designed to generate an alternating current at its secondary windings, which is proportional to the current measured at its primary windings.
16. Give the reasons of systematic errors?
The main reasons foe systematic errors are: Environmental error, Observational error, and Instrumental error
17. Discuss about the accuracy of a measurement?
How close the measured value to its actual values refers to the accuracy of a measurement. In other words, we can say that the closeness (exactness) of measured value to its correct value is termed as the accuracy.
18. Write down the equation for correction factor of an instrument transformer?
The correction factor of an instrument transformer can be obtained as:
Correction factor = (Transformation ratio)/(The nominal ratio)
19. Define the phase angle of an instrument transformer?
For a current transformer, the phase angle can be defined as the angle between the primary current Ip and the secondary current Is at reversed condition.
20. Mention the device that is used in a CRT for the source emission of electrons?
The device used for source emission of electrons in CRT is a barium and strontium oxide coated cathode.
21. What you know about the function probe in a CRO?
In an electronic circuit, it is mandatory to see all the waveforms. The device used for this purpose is a CRO. For connecting the test circuit (from bread board) to oscilloscope with out altering or loading, probes are used. In other words, we can say that for distributing the test circuit, probes are used.
22. What you understand about measurement?
Simply we can say that measurement is the process of determining the degree, amount or capacity (direct or indirect) by comparison with the usual standards.
23. Mention the three different categories of error?
The different categories of errors are: Gross error, Systematic error, Random error
24. Write down the equation for the turns ratio of instrument transformer?
Turns Ratio = (The number of turns in secondary winding of an instrument transformer)/(The number of turns in primary winding of an instrument transformer)
25. What you understand about voltage transformers?
Voltage transformers (also known as potential transformers) are mainly used for measuring the voltage of a circuit.
26. Mention the basic components of a CRO?
The main components of CRO are:
• Vertical deflection system
• Horizontal deflection system
• Synchronization circuit
• Blanking circuit
• Intensity modulation
• Position control
• Focus control
• Cathode ray tube
• Calibration circuit
27. Discuss the need of attenuator in CRO?
For reducing the amplitude of the vertical input signal before applying to vertical amplifier, an attenuator is used. Between the vertical input terminals of the vertical amplifier, an attenuator is placed (for displaying high amplitude signals).
28. What you know about the gross error?
Because of human mistakes in reading or error in observation recordings (or by using instruments), gross errors are occurred. It can also occur because of incorrect adjustment of instruments and computational mistakes. we can cannot mathematically treat these types of errors.
29. Mention the different types of probes used in CRO. Discuss the functions of each probe?
Different types of probes used in CRO are direct probe, Isolation probes and detector probe.
Direct Probe: For low frequency and low impedance circuits, direct probes are used. At the time of measuring low level signals, stay-pick up may occurs and may create problems. For avoiding this, direct probes are used.
Isolation Probe: For avoiding the undesirable circuit loading effects of the shielded probe, isolation probes are used.
Detector Probe: In order to separate the low frequency components from high frequency components, detector probes are used. The main use of detector probes are in analyzing the response to modulated signals used in communication equipments. The main applications of detector probes are: AM, FM and TV Receivers.