EI (2 MARKS) UNIT IV

Unit IV

1.Explain the principle of ramp type DVM?

The operating principle isto measure the time taken by a linear ramp to change the input level to ground level and viceversa.

2.Explain the principle of dual slope DVM?

The input voltage is integrated over a fixed time period.After the fixed time period the input voltage is disconnected and a negative input is connected.The output will have a negative slope which is constant and proportional to magnitude of input voltage.

3.Explain the principle of successive approximation type DVM?

The principle of sucessive approximation type DVM is similar to that of measuring the weight of an unknown quantity by using a balance

Ie: At each stage Vin is compared with the reference input.If Vin>Vref then the control circuit set that particular bit and Vref jumps to half of the reference voltage

If Vin then the control circuit will reset that particular bit,such a kind of measurement is completed in 8-clock pulses.

4.Explain the principle of digital frequency meter?

The signal whose frequency to be measured is converted to trigger pulses and applied continuously to an AND gate at one of the input terminal and at the other input terminal a pulse signal is applied.This pulse signal should have a suitable time period.pulses occurring at the output during this time interval is counted and this corresponds to the frequency to be measured.

5.Name the attenuation techniques used for high frequency measurement?

Ø Prescaling

Ø Hetrodyne converter

Ø Transfer oscillator

Ø Automatic divider

6.State the advantage of dual slope integrating type DVM over ramp type DVM?

In ramp techniques,superimposed noise can cause large errors.In dual ramp technique,noise is averaged out by the positive and negative ramps using the process of integration.

7.What is automatic polarity?

In a microprocessor based DMM the counter sends two clock signals to the programming unit,one just before the end of integration period and the one just after the end of integation period.The first signal is used by the polarity detector,hence to determine the polarity of the input signal .This is called automatic polarity.

8.Draw the simple sample and Hold circuit?

9.What is sample and Hold circuit?

Sample and hold circuit is one which is used to convert analog signal to digita signal.

10.Draw the output waveform of a sample and hold circuit?

11.State the advantage of successive approximation method?

The main advantage of SAR DVM is that is very fast.At the best it takes ‘n’ clock pulse to produce ‘n’ bit result.The SAR method is more faster than counter method.

12.State the drawbacks of Ramp-type DVM?

In ramp type DVM noise present in the input signal will cause a lot of errors in the output.

13.Define LCR meter?

LCR meter is an instrument which is used to measure inductance,capacitance and resistance.

14.Define ‘Q’?

Q= Ratio of inductance(or) capacitive resonance

Resistance

15.What is the basic principle of a digital storage oscilloscope?

The basic principle in a digital storage oscilloscope is the conversion of analog input signal into a digital form using A/D converter and then this digital signal

Is stored in the oscilloscope’s memory.

16.Draw the basic circuit for a ‘Q’ meter?

17.What’s the principle of the ’Q’ meter and state its use?

The Q meter is an instrument designed to measure some electrical properties of coils and capacitors.

18.Draw the block diagram of a digital storage oscilloscope?

19.Define sampling rate in a digital storage oscilloscope?

In a digital storage oscilloscope the A/D sample clock determines howoften the ADC takes a sample.This rate is called sample rate and is expressed in samples per second.

20.State the advantages and limitations of digital storage oscilloscope?

Advantages:

Ø Split-screen capability.

Ø Pre-trigger capability

Ø Display the stored data in amplitude Vs time period and X-Y mode are possible.

Limitations:

Ø Band-width limitations.