Important Short Questions and Answers: Measurements and Instrumentation - Introduction

INTRODUCTION

1. What is meant by measurement?

Measurement means an act or the result of comparison between the quantity and a

predefined standard.

2.   Mention the basic requirements of measurement.

The basic requirements of measurement are

i.    The standard used for comparison purpose must be accurately defined and should be commonly accepted.

ii.   The apparatus used and the method adopted must be provable.

3.   State  the  two  methods  for measurement.

The two methods of measurement are

i. Direct method and

ii. Indirect method.

4. State the function of measurement system.

The measurement system consists of a transducing element which converts the quantity to be measured in an analogous form the analogous signal is then processed by some intermediate means and is then fed to the end device which presents the results of the measurement.

5.   List the three types of instruments.

The three types of instruments are:

i.    Mechanical Instruments

ii.   Electrical Instruments and

iii. Electronic Instruments.

6.   Classify the instrument based on their functions.

Instruments are classified into three types based on their functions. They are

i.    Indicating instruments

ii. Integrating instruments

iii. Recording instruments

7. Give any three applications of measurement systems.

The applications of measurement systems are

i.    Monitoring of processes and operations.

ii.   Control of  processes and operations.

iii.  Experimental engineering analysis.

8. Why calibration of instrument is important?

The calibration of all instruments is important since it affords the opportunity to check the instrument against a known standard and subsequently to errors in accuracy.

9. List the calibration procedure.

Calibration procedure involves a comparison of the particular instrument with either.

A primary standard

A secondary standard with a higher accuracy than the instrument to be calibrated or An instrument of known accuracy.

10. Define: Calibration

Calibration is defined as the process by which comparing the instrument with a standard to correct the accuracy.

11. Mention the functions performed by the measurement system.

The functions performed by the measurement system are

i. Indicating function

ii.    Recording function

iii. Controlling function

12. List the functional elements of the measurement systems.

The three main functional elements of the measurement systems are:

i. Primary sensing element

ii. Variable conversion element

iii. Data presentation element

13. Write the characteristics of the measurement system.

Characteristics of measurement system is divided into two categories:

i.    Static characteristics

ii.   Dynamic characteristics

14. Write the main static characteristics?

The main static characteristics are:

i. Accuracy

 ii. Sensitivity

iii. Reproducibility

iv. Drift

v. Static error

vi. Dead zone

vii. Resolution

viii. Precision

ix. Repeatability

x. Stability

15. Define static error

Static error is defined as the difference between the true value and the measured value of the quantity. Static error

= A_t – A_m

where

A_m =measured value of quantity

A_t =true value of quantity.

16. Define resolution

Resolution is defined as the smallest increment of quantity being measured which can be detected with certainty being measured which can be detected with certainty by an instrument.

17. Define threshold

Threshold is defined as the minimum value of the input at which the output starts

changing/increasing from zero.

18. Define linearity

The linearity is defined as the ability to reproduce the input characteristics symmetrically and linearly.

19. Define reproducibility

Reproducibility is defined as the degree of closeness with which a given value may be repeatedly measured. It is specified in terms of scale readings over a given period of time.

20. Define drift

Drift is defined as slow variation of reading from a fixed value.

21. Define speed response

Speed response is defined as the rapidity with which a measurement system responds to changes in measured quantity. It is one of the dynamic characteristics of a measurement system.

22. Define fidelity

Fidelity is defined as the degree to which a measurement system indicates changes in the measured quantity without any dynamic error.

23. Define dynamic error

Dynamic error is defined as the difference between the true value of the quantity changing with time and the value indicated by the measurement system if no static error is assumed. It is also called measurement error. It is one the dynamic characteristics.

24.Define retardation delay

Retardation delay is defined as the retardation delay in the response of a measurement system to changes in the measured quantity.

25. Define time delay

Time delay is defined as the response of the measurement system begins after a dead zone after the application of the input.