2. Name the potentiometer material used.
(i)German silver (ii)Manganin wire
3. Define standardization.
It is the process by which adjusting the current flows through the potentiometer coil to make the voltage across the std cell is equal.
4. State the applications of potentiometer.
(i)Used for m/s of unknown emf (ii) Used for ammeter calibration (iii)Used for Voltmeter calibration(iv)Used for wattmeter calibration
5. What are the various types of signal generators?
(ι) Sweep signal generator (ii) Audio frequency signal generator (ιιι) RF signal generators
6. What are the types of frequency synthesizer?
There are two methods of frequency synthesis, they are (i) Direct frequency synthesis (ii)In-direct frequency synthesis
7. What is meant by harmonic distortion?
Any unwanted harmonics that are present along with the needful information is known as Harmonic Distortion.
8. How the phase angle is measured in polar type potentiometers?.
It is measured from the position of phase shifter.
9. Name some ac potentiometers.?
Drysdale Tinsley potentiometer Gall Tinsley potentiometer.
10. State the advantages of ac potentiometers?.
Can be used for m/s of both magnitude and phase angle Can be used for m/s of inductance of the coil. It is used in m/s of errors in CTS.
11. State the applications of ac potentiometers.
(i)M/s of self inductance.(ii)Ammeter calibration, (iii)Voltmeter calibration (iv) Wattmeter calibration..
12. What are Detectors?
Detectors are used in an attempt to adequately map the correct signal power
to the appropriate frequency point on the display. There are in general three types of detectors: sample, peak, and average
Sample detection – sample detection simply uses the midpoint of a given interval as the display point value. While this method does represent random noise well, it does not always capture all sinusoidal signals.
Peak detection – peak detection uses the maximum measured point within agiven interval as the display point value. This insures that the maximumsinusoid is measured within the interval; however, smaller sinusoids withinthe interval may not be measured. Also, peak detection does not give a good representation of random noise.
Average detection – average detection uses all of the data points within theinterval to consider the display point value. This is done by power (rms)averaging, voltage averaging, or log-power averaging.
13. State the disadvantage of instrument transformers?
Cannot be used for dc measurements.
14. What are the constructional parts of current transformer?
(i)Primary winding,(ii)Secondary winding (iii)Magnetic core.
15. Name the errors caused in current transformer?.
Ratio error and Phase angle error.
16. What is meant by Resolution Bandwidth?
The resolution bandwidth filter or RBW filter is the bandpass filter in the IF path. Adjusting the bandwidth of this filter allows for the discrimination of signals with closely spaced frequency components, while also changing the measured noise floor. Decreasing the bandwidth of RBW filter decreases the measured noise floor and vice-versa. This is due to higher RBW filters passing more frequency components through to the envelope detector than lower bandwidth RBW filters, therefore a higher RBW causes a higher measured noise floor.
17. What is meant by Wave analyzer?
Wave analyzer helps to evaluate the characteristics of wave such as frequency, amplitude and Phase angle.
18. What is a Spectrum Analyzer?
Spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals. The input signal a spectrum analyzer measures is electrical, however, spectral compositions of other signals, such as acoustic pressure waves and optical light waves, can be considered through the use of an appropriate transducer.
19. What are the types of Spectrum Analyzer?
Spectrum analyzer types are dictated by the methods used to obtain the spectrum of a signal. There are swept-tuned and FFT based spectrum analyzers:
A swept-tuned spectrum analyzer uses a superheterodyne receiver to downconvert a portion of the input signal spectrum (using a voltage-controlled oscillator and a mixer) to the center frequency of a band-pass filter. With a superheterodyne architecture, the voltage-controlled oscillator is swept through a range of frequencies, enabling the consideration of the full frequency range of the instrument.
A FFT spectrum analyzer computes the discrete Fourier transform (DFT), a mathematical process that transforms a waveform into the components of its frequency spectrum, of the input signal.
Some spectrum analyzers, such as real-time spectrum analyzers, use a hybrid technique where the incoming signal is first down-converted to a lower frequency
using superheterodyne techniques and then analyzed using fast fourier transformation (FFT) techniques.
20. What is meant by center frequency?
In a typical spectrum analyzer there are options to set the start, stop, and center frequency. The frequency between the stop and start frequencies on a spectrum analyzer display is known as the center frequency. This is the frequency that is in the middle of the display’s frequency axis. Span specifies the range between the start and stop frequencies. These two parameters allow for adjustment of the display within the frequency range of the instrument to enhance visibility of the spectrum measured.
UNIT-IV DIGITAL INSTRUMENTS
1. What is a Voltmeter?
