BIOLOGICAL SYSTEMS INSTRUMENTATION

EAB 3602DR. SAMSUZANA ABD AZIZsuzana@eng.upm.edu.my

Ext: 4326

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INTRODUCTION

• Class schedule: Teusday, 8 am - 10 pm, BK10• Lab: Wednesday 2-5 pm (starts next week)– Instrumentation Lab, KEE (Tower, Level 6) :Lab 1-7– Makmal Pemprosesan BahanBio, KBP: Lab 8-10

• Grading:– Quiz & Assignment: 10 %– Lab : 20 %– Test 1 & 2 : 30 %– Final Exam : 40 %

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• References:– Fundamentals of Electricity for Agriculture- Robert

J Gustafon and Mark T Morgan 2004. 3rd Edition.– Electronic Instrumentation – H S Kalsi, 2004

(McGraw-Hill , 2nd Edition)– Introduction to Instrumentation and

Measurements – Robert B. Northrop, 2005 (CRC Press , 2nd Edition)

– Notes and Handouts

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Lecture 1ELECTRONIC MEASUREMENT

SYSTEMS

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Introduction

• To introduce electronic instrumentation systems so the students will acquire an ability to make accurate and meaningful measurements of mechanical and thermal quantity.

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Introduction

• Instrumentation is a technology of measurement

• Measuring is basically used to monitor a process or operation, or as well as the controlling process.

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Quantity

• Mechanical quantity:– Strain, force, pressure, moment, torque,

displacement, velocity, acceleration, flow velocity, mass flow rate, volume flow rate, frequency, and time

• Thermal quantity:– Temperature, heat flux, specific heat, and thermal

conductivity

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Electronic Instrumentation System

Power Supply Transducer

Conditioning Circuit

Amplifier

Recorder Data processor Engineering Analysis

Power supply provides the energy to drive the transducer

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Electronic Instrumentation System

Power Supply Transducer

Conditioning Circuit

Amplifier

Recorder Data processor Engineering Analysis

The transducer is an analog device that converts a change in the mechanical or thermal quantity being measured into a change of electrical quantity.

E.g. ∆Strain --- ∆Resistance

Strain gage type transducers

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Electronic Instrumentation System

Power Supply Transducer

Conditioning Circuit

Amplifier

Recorder Data processor Engineering Analysis

Signal conditioners are electronic circuit that convert, compensate, or manipulate the output from the transducer into a more usable electrical quantity.

E.g. ∆resistance --- ∆voltage using a Wheatstone Bridge

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Electronic Instrumentation System

Power Supply Transducer

Conditioning Circuit

Amplifier

Recorder Data processor Engineering Analysis

Amplifiers are required in the system when the voltage output from the transducer-signal conditioner combinations is small.

E.g. Amplifier with gains of 10 to 1000 are used to increase the signals to level (1-10V) that are compatible with the voltage-measuring devices used in the system.

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Electronic Instrumentation System

Power Supply Transducer

Conditioning Circuit

Amplifier

Recorder Data processor Engineering Analysis

Recorders are voltage-measuring devices used to display the measurement in a form that can be read and interpreted. Recorders may be analog (oscilloscopes and magnetic ape recorder) or digital (numerical array).

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Electronic Instrumentation System

Power Supply Transducer

Conditioning Circuit

Amplifier

Recorder Data processor Engineering Analysis

Data processors are used with instrument systems that incorporate analog- to-digital converters (A.D) and provide the output signal presenting the measurement in a digital code. The output from the processor is displayed in graphs or tables. Example: Computer

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Electronic Instrumentation System

Power Supply Transducer

Conditioning Circuit

Amplifier

Recorder Data processor Engineering Analysis

An Engineering analysis is conducted to evaluate new or modified designs of a machine component, structure, electronic system, or vehicle to ensure efficient and reliable performance when the prototype is placed in operation.

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QUALITIES OF MEASUREMENTS

• PERFORMANCE CHARACTERISTICS– Static– Dynamic

• HOW TO QUANTIFY?– Error Measurements– Statistical Analysis

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STATIC CHARACTERISTICS

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CHARACTERISTICS OF MEASUREMENT SYSTEMS

• Static Characteristic:– used to define the performance criteria for the

measurement of quantities that remain constant(Considered for instrument to measure unvarying

process condition)

Measurement Errors

• Deviation of a reading from the expected value of the measured variable

• Extent of measurement error must be stated with the measurement

• Error in measurement is expressed as absolute error or percentage of error

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Error Calculation

Absolute error (e)

The difference between the expected (Yn) and the measured (Xn) value of a variable

Percentage of error

e = Yn - Xn

Percent error = (100)Yn

Yn - Xn

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Types of Static Errors

• Divided into four categories:–Gross Errors–Systematic Errors–Random Errors–Limiting Errors

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Gross Errors

• Generally the fault of the person using the measuring instrument such as incorrect reading, incorrect recording, incorrect use etc

• Avoidable and must be identified and minimized if not eliminated

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Systematic Errors

• Probable causes:– Instrument error– Environmental effect– Observational errors

• Causes shall be identified and corrected

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Random Errors

o Generally an accumulation of large numbers of small inherent causes

o Shall be statistically analyzed and reduced

o Prompt for better accuracy and precise instrument

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Limiting Errors

o Manufacturing limitation to the accuracy of an instrument

o Stated as percentage of full-scale deflection

o Increases as measured value less than full-scale deflection

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Limiting Errors (cont’d)

• Example:

A 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.

The magnitude of the limiting error is

2/100 x 300 = 6V

Therefore, the limiting error at 120 V is

6/120 x 100 = 5%

(reading < full scale, limiting error increased)

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• Accuracy – The degree of exactness

of a measurement compared to the expected value

A = 1 - Yn

Yn - Xn

Accuracy vs. Precision

• Precision– A measure of consistency,

or repeatability of measurements

Xn - XnPrecision = 1 -Xn

Xn = the value of the nth measurement

nX = the average of the set of n measurements

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Example

The expected value of the voltage across a resistoris 5.0V. However, measurement yields a value of4.9V. Calculate:

a) absolute error (0.1)b)% error (2%)c) relative accuracy (0.98)d) % accuracy (98%)

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CHARACTERISTICS OF MEASUREMENT SYSTEMS

• Dynamic Characteristic– Concerned with the relationship between the

system input and output when the measured quantity is varying rapidly

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Dynamic Characteristic

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Example:

Measurement Uncertainty

• Probability that a reading falls within the interval that contain true value

• Confidence level for margin of errors• Statistically determined• Reflect instrument imprecision

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Statistical Analysis of Error in Measurement

oMean value/ Arithmetic Mean oDeviationoAverage deviation (D)oStandard deviation (S)

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n

1i

n321 x x x x

n

x

nx i

Arithmetic mean/average

n = total number of piece of data

xn = the value of the nth measurement

xi = set of number

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Deviation

• The difference between each piece of data and arithmetic mean

xxd nn * Note

0 21 ntot dddd

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Average deviation (D)

• precision of a measuring instrument

- high D low precision

- low D high precision

n

dddD n

21

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Standard deviation (S)

• The degree to which the value vary about the average value

30nfor

1

1 1

2

1

2

n

d

n

xxS

n

ii

n

ii

30 n for 1

2

n

dS

n

ii

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ExampleFor the following data compute

(a) The arithmetic mean (49.9)

(b) The deviation of each value (0.2,-0.2,-0.3,0.3)

(c) The algebraic sum of the deviation (0)

(d) The average deviation (0.25)

(e) The standard deviation (0.294)

x1= 50.1

x2= 49.7

x3= 49.6

x4= 50.2

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Calibration

• Process of establishing the relation between the indication of a measuring instrument and the value of a measurement standard

• Traceability to International Standard• Calibration improve accuracy

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THE END

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