lecture notes 02.ppt

Chapter 01

Introduction to Instrumentation & Measurements.

Warm-ups (5 min)

Getting-to-know Session:Students are given a list of students

attributes, and they should get initial from the specific students.

Share the experiencesAppointment of a Class Rep and his/her

Assistant.

Objectives

At the end of this chapter, the students should be able to:

explain units and quantities in electrical.discuss and calculate various types of

error in measurement.Explain the meaning of some terms in

instrumentation field.

Outlines

The outline of this chapter is as follow:Principles of instrumentation

and measurementsElectrical UnitsError in measurementSome terms +definitions in

instrumentations.

Introduction

Why learning BEE1313?What is the main role/ purpose of

instrumentation?Give Example of applications?

Introduction

Instrumentations serve three (3) basic functions: -

indicating…

recording…

controlling…

Fundamental Quantity…

Quantity Symbol Unit Unit Abbre.

Length l meter m

Mass m kilogram kg

Time t second s

Temperature T Kelvin oK

Electric current I Ampere A

Electrical Units

Derived Quantity…

Quantity Symbol Unit Unit Abbre.

emf/ voltage V volt V

charge Q coulomb C

resistance R Ohm Ω

capacitance C farad F

inductance L hendry H

Electrical Units

Measurement Standards

Standards are defined in 4 categories:international standards.primary standards.secondary standards.working standards.

Measurement Standards

Mass- kg defined the mass of an alloy cyllinder Standards are defined in 4 categories:international standards.primary standards.secondary standards.working standards.

Error in Measurement

There are various types of error in measurement:

absolute errorgross errorsystematic errorrandom errorlimiting error

Error in Measurement

What is the meaning of error?

Please define.

------------------------------------------------------

Error in Measurement

Error - The deviation of a reading or set of readings from the expected value of the measured variable.

Error in Measurement

Absolute error.

Absolute error maybe defined as the difference between the expected value of the variable and the measured value of the variable, or

e = Yn – Xnwhere:

e = absolute error.

Yn = expected value.

Xn = measured value

Error in Measurement

to express error in percentage

% error =

we also derived relative accuracy, A;

)100(nY

e

n

nn

Y

XYA

1

Error in Measurement

Example 1-1.

The expected value of the voltage across a resistor is 5.0 V. However, measurement yields a value of 4.9 V. Calculate:

a) absolute error

b) % error

c) relative accuracy

d) % accuracy

Error in Measurement

Errors are generally categorized under the following three (3) major headings:Gross ErrorsSystematic ErrorsRandom Errors

Error in Measurement

Gross Error generally the fault of the person

using the instrumentssuch as incorrect reading, incorrect

recording, incorrect use etc.

Error in Measurement

Systematic Error due to problems with instruments/

environmental effects/ or observational errors.

Example…??? parallax errorwrong estimation reading scale

Error in Measurement

Random Errors generally the accumulation of a large

number of small effectsmaybe of real concern only in

measurements requiring a high degree of accuracy.

such errors can only be analyzed statistically.

Error in Measurement

Limiting Errors manufacturers of instruments state that

an instrument is accurate within a certain percentage of a full-scale reading.

example is; a voltmeter is accurate within ±2% at full-scale deflection.

this specification is called the limiting errors.

Error in Measurement

Limiting Errors However, with reading less than full-

scale, the limiting error will increase.therefore, it is important to obtain

measurements as close as possible to full scale.

Error in Measurement

Example 1-2A 300-V voltmeter is specified to be accurate within ±2% at full scale. Calculate the limiting error when the instrument is used to measure a 120-V source?

Error in Measurement

Example 1-3A voltmeter and an ammeter are to be used to determine the power dissipated in a resistor. Both instruments are guaranteed to be accurate within ±1% at full scale. If the voltmeter reads 80V on its 150-V range and the ammeter reads 70mA on its 100-mA range, calculate the limiting error for the power calculation.

Summary

Some terms +definitions are as below: Error – ---??? Accuracy – The degree of exactness of a

measurement compared to the expected value

Precision – A measure of consistency, or repeatability of measurements.

Summary

Instrument – a device or mechanism used to determine the present value of a quantity

Measurement – a process of comparing an unknown quantity with an accepted standard quantity.

Standard – an instrument or device having a recognized permanent (stable) value that is used as a reference.

Summary

expected value – the most probable value we should expect to obtain.

deviation – the difference between any piece of data in a set of numbers and the arithmetic mean of the set of numbers.

transducer – a device that converts one form of energy into another form

Electrical Quantity…

Quantity Symbol Unit Unit Abbre.

l meter

Capacitance F

Time second

T Kelvin oK

Charge

Evaluation

Evaluation

Quiz 01