Electrical Measurements Lab Viva Questions and Answers

Question No. 01: What is gross error?
Answer: These errors are mainly due to human mistakes in reading or in using instruments or error in recording observations. This error also occurs due to incorrect adjustment of instruments and computational mistakes these errors cannot treat mathematically.

Question No. 02: What is the function of Attenuator in CRO?
Answer: The voltage in input terminal of the vertical amplifier causes the beam to deflect off the CRT screen, is unite low in amplitude. So that high amplitude signals may be displayed, an attenuator network is placed between the vertical input terminals of the vertical amplifier. The main function of the attenuator is to reduce the amplitude of the vertical input signal before applying it to vertical amplifier.

Question No. 03: What are the basic components of a CRO?
Answer: CRO Circuit consists of following components:
  1. Vertical deflection system
  2. Horizontal deflection system
  3. Synchronization circuit
  4. Blanking circuit
  5. Intensity modulation
  6. Position control
  7. Focus control
  8. Cathode ray tube
  9. Calibration circuit

Question No. 04: What do you mean by a Voltage transformer?
Answer: The transformers used for voltage measurement are called voltage or potential transformer.

Question No. 05: What do you mean by Turns ratio of instrument transformer?
Answer: It is the ratio of number of turns in secondary winding to the number of turns in primary winding of an instrument transformer.

Question No. 06: What are the three major categories of error?
Answer: Error may arise from different sources and are usually classified as:
  1. Gross error
  2. Systematic error
  3. Random error

Question No. 07: What is measurement?
Answer: The process of determining the amount, degree, or capacity by comparison (direct or indirect) with the accepted standards of the system units being used.

Question No. 08: What is the function of probe in CRO?
Answer: The probe performs the very important function of connecting the test circuit to oscilloscope without altering, loading or otherwise disturbing the test circuit.

Question No. 09: Which device is used for the source of emission of electrons in a CRT?
Answer: A barium and strontium oxide coated cathode is used for the source of emission of electrons in a CRT.

Question No. 10: What is the function of electron-gun used in CRT?
Answer: The source of focused and accelerated electrons beam is the electron gun. The electron gun emits electrons and forms them into a beam consist of a heater, a cathode, a grid, a pre-accelerating anode, a focusing anode and an accelerating anode.

Question No. 11: What do you mean by a phase Angel of instrument transformer?
Answer: The angle between secondary current and primary current of a current transformer is called phase angle of instrument transformer.

Question No. 01: What do you mean by ratio correction factor of instrument transformer?
Answer: It is the ratio of the transformation ratio to the nominal ratio of an instrument transformer.

Question No. 12: What is accuracy of a measurement?
Answer: The degree of exactness (closeness) of a measurement compared to the expected (desired) value.

Question No. 13: Why Systematic errors occur?
Answer: These error occur due to
  1. Instrumental error
  2. Environmental error
  3. Observational error

Question No. 14: What are the functions of different probes used in CRO?
Answer:
Direct Probe: direct probe avoids stay-pick up which may create problems when low level signals are being measured. It is used for low frequency or low impedance circuit. Isolation probe: Isolation probe is used in order to avoid the undesirable circuit loading effects of the shielded probe.
Detector probe: when analyzing the response to modulated signals used in Communications equipment like AM, FM and TV receivers, the detector probe functions to separate the low frequency modulation component from the high frequency carrier.

Question No. 15: What do you mean by a Current transformer?
Answer: The transformers which are used for measurement of current is called current transformer.

Question No. 16: What do you mean by Nominal ratio of instrument transformer?
Answer: It is the ratio of rated primary winding current to the rated secondary winding current of an instrument transformer.

Question No. 17: What is Resolution of a measurement?
Answer: The smallest change in a measured variable to which an instrument will respond.

Question No. 18: What are the reasons of instrumental error?
Answer: The instrumental errors arise due to three main reasons:
  1. Due to inherent shortcoming in the instrument
  2. Due to misuse of the instruments
  3. Due to loading effect of instrument

Question No. 19: What is the function of electron-gun assembly used in CRT?
Answer: The electron gun assembly produces a sharply focused beam of electrons which are accelerated to high velocity .this focused beam of electrons strikes the fluorescent screen with sufficient energy to cause a luminous spot on the screen.

Question No. 20: What do you mean by transformation ratio of instrument transformer?
Answer: It is the ratio of primary winding current to the secondary winding current of an instrument transformer.

Question No. 21: What is precision of a measurement?
Answer: A measure of the consistency or repeatability of measurement, i.e. successive reading do not differ.

Question No. 22: How many types of probe used in CRO?
Answer: There are three types of probe used in CRO:
  1. Direct probe
  2. Isolation probe
  3. Detector probe

Question No. 23: What is Error of a measurement?
Answer: The deviation of the change in output (response) of the instrument to a change of input or measured variable.

Question No. 24: What are the types of instrument transformer?
Answer: There are two types of instrument transformer:
  1. Current transformer
  2. Voltage transformer

Question No. 25: What is Sensitivity of a measurement?
Answer: The ratio of the change in output (response) of the instrument to a change of input or measured variable.

Question No. 26: What do you mean by an instrument transformer?
Answer: Transformer which is used with measuring instrument is called instrument transformers. Instrument transformer is used as a protection circuit of power system for the operation of over current, under voltage, Earth fault etc.

Question No. 27: What is Cathode ray oscilloscope (CRO)?
Answer: Cathode ray oscilloscope is an instrument used for display, measurement and analysis of waveforms and other phenomenon in electrical and electronic circuit.

Question No. 28: What are the Advantages of instrument transformer?
Answer: Advantages of instrument transformer are:
  1. Instrument transformers are moderate in size and used for 5 A current and 100 to 200 V measurements.
  2. Instruments using instrument transformer are low cost.
  3. Replacement of damage parts is Easy.
  4. The metering circuit is isolated the high voltage power circuit hence insulation and safety is assured for operation.
  5. There is low power consumption in metering circuit.

Question No. 29: What is the function of aquadag in a CRO?
Answer: An aquadag is used in a CRO to collect secondary emission electrons.
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