electrical measurements viva questions with Answers
1 what is measurement?
The process of determining the amount, degree, or capacity by comparison (direct or indirect) with the accepted standards of the system units being used.
2 what is accuracy of a measurement?
The degree of exactness (closeness) of a measurement compared to the expected (desired) value.
3 what is Resolution of a measurement?
The smallest change in a measured variable to which an instrument will respond.
4 what is precision of a measurement?
A measure of the consistency or repeatability of measurement, i.e. successive reading do not differ.
5 what is Sensitivity of a measurement?
The ratio of the change in output (response) of the instrument to a change of input or measured
variable.
6 what is Error of a measurement?
The deviation of the change in output (response) of the instrument to a change of input or measured
variable.
7 what are the three major categories of error?
Error may arise from different sources and are usually classified as
1 Gross error 2. Systematic error 3. Random error
8 what is gross error?
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 can not treat mathematically.
9 what is Systematic error?
These error occur due1. Instrumental error 2. Environmental error 3. Observational error
10 what is instrumental error?
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
11.what is Cathode ray oscilloscope (CRO)?
Cathode ray oscilloscope is a instrument used for display, measurement and analysis of
waveforms and other phenomenon in electrical and electronic circuit
12.what are the basic component of a CRO?
CRO Circuit consists of following components:
1. Vertical deflection system 2. Horizontal deflection system 3.Synchronization circuit
4. Blanking circuit 5 Intensity modulation 6position control
7. Focus control 8. Cathode ray tube 9. Calibration circuit
13.what is the function of probe in CRO?
The probe performs the very important function of connecting the test circuit to oscilloscope
without altering, loading or otherwise disturbing the test circuit.
14 how many types of probe used in CRO?
There are three types of probe used in CRO:
1 Direct probe 2. Isolation probe 3. Detector probe
15.what are the functions of different probes used in CRO?
Direct Probe: direct probe avoids stay-pick up which may create problems when low level signals
are being measured. It is used for low freuency 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 freuency carrier.
16.what is the function of Attenuator in CRO?
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.
17.which device is used for the source of emission of electrons in a CRT?
A barium and strontium oxide coated cathode is used for the source of emission of electrons in a
CRT.
18.what is the function of Auadag in a CRO?
Ans: An Audage is used in a CRO to collect secondary emission electrons.
19.what is the function of electron gun assembly used in CRT?
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.
20 what is the function of electron gun used in CRT?
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.
21.What do you mean by an instrument transformer?
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.
22.what are the types of instrument transformer?
there are two types of instrument transformer:
1. Current transformer 2. Voltage transformer
23.What do you mean by a Current transformer?
The transformers which are used for measurement of current is called current transformer.
24.what do you mean by a Voltage transformer?
The transformers used for voltage measurement are called voltage or potential transformer.
25.what are the Advantages of instrument transformer?
Advantages of instrument transformer are:
1. Instrument transformers are moderate in size and used for 5A current and 100 to 200 V
measurement.
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 safty is
assured for operation.
5. There is low power consumption in metering circuit.
26.what do you mean by a phase Angel of instrument transformer?
The angle between secondary current and primary current of a current transformer is called phase angle of instrument transformer.
27.what do you mean by transformation ratio of instrument transformer?
It is the ratio of primary winding current to the secondary winding current of an instrument
transformer.
28.what do you mean by Nominal ratio of instrument transformer?
It is the ratio of rated primary winding current to the rated secondary winding current of an
instrument transformer.
29.what do you mean by Turns ratio of instrument transformer?
It is the ratio of number of turns in secondary winding to the number of turns in primary winding of an instrument transformer.
30.what do you mean by ratio correction factor of instrument transformer?
It is the ratio of the transformation ratio to the nominal ratio of an instrument transformer
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