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AU 351 Sensor Technology in Automotive EngineeringFaculty of Engineer ingThammasat University

AU 351Sensors Technology

in Automotive Engineering

by

Asst. Prof.Dr. Channarong Asavatesanupap

Faculty of Engineer ingThammasat University

AU 351 Sensor Technology in Automotive Engineering


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Chap 1 Fundamentals of Measurement

Measurementprocess

Reference

Physical Quantity

magnitude ofthe quantity

Measurement is the process of determining the magnitude of a physical quantity, such as length or mass, relative to a unit of measurement (Reference).

Faculty of Engineer ingThammasat University


คณะวิศวกรรมศาสตร์

มหาวิทยลยัธรรมศาสตร์

What important?

- Accuracy

- Margin of error

- Confidence level

Example

Physical quantityHeight (Length)

Measurementprocess

ReferenceMeasuring tape

magnitude ofthe quantity

= 1.60 m



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Measuring devices



distance

MassTemperature

Pressure

Measuring deviceconverts this sensed information into a

detectable signal

PhysicalQuantity

Signalelectrical, mechanical,

optical, or otherwise




Basic measuring devices

Sensor

Transducer

Output

Sensor

Transducer

Output on display scale

is a physical element that employs some natural phenomenon by which it senses the variable being measured.

converts the sensed information into detectable signal.



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Example: Thermometer

bulb

Thermometersensor

TemperatureThermal Expansion

of the liquid

Liquid contained within the bulb exchanges energy with its surrounding until they reach thermal equilibrium. As a result, the liquid moves up and down the stem due to the thermal expansion.




Electronic measurement system

Transducer

Conditioningcircuits

Amplifier

Recorder

Dataprocessor

Controller

Powersupply

Commandgenerator

For engineering analysis- Graphs or Tables

Process control



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Transducer


Amplifier

Recorder

Dataprocessor

Controller

Powersupply

Commandgenerator

Transducer converts the physical change from the sensor into the signal.

T VThermocouple

Amplifier increases the power of the desired signal to the desired magnitude.

Conditioning circuit takes the transducer signal and modifies it to a desired signal.





Data processor is used with the measurement system that incorporate analog-to-digital converters (A/D) and provides the output signal representing the measurement in a digital code.

Recorder is a voltage-measuring device used to display the measurement.

Analog recorders

Digitalrecorders

Controller is used to monitor and adjust any quantity that must be maintained at a specified value to produce a material or product in a controlled process.

Transducer


Amplifier

Recorder

Dataprocessor

Controller

Powersupply

Commandgenerator




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Transducer

TransducerMechanical energy

orThermal energy

Electrical energy

converts the physical change from the sensor into the detectable signal. In other words, transducer is a device that converts one form energy to another.

Resistance,Voltage,Current,

etc

Strain,Temperature,

Pressure,etc

Input, Qi Output, Qo




Calibration

is a comparison between measurements – a known input value (standard) is applied to a measurement system for the purpose of observing the system output value. The relationship between the input and output values is then established.

1. Static calibration: a known value is input to the system under calibration and the system output is recorded. The input values remain constant, i.e. they do not vary with time or space.

Qo = f (Qi)

2. Dynamic calibration: when the inputs are time (or space) dependent.



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***The calibration curve will have the form y=f(x) and can be used in later measurements to ascertain the unknown input value based on the output value.




Calibration curve interpretation

Qo

Qi

Least-squaresfit to data

ZeroOffset , Z0

Deviationfrom linearity

Span

Allowable deviation

Slope = S = senstivity

Range

Many instruments are designed to achieve a linear relationship between the applied input and indicated output values as shown in the figure



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Characteristics of measurement system

2) Slope of a calibration curve provides the static sensitivity, S (calibration constant) of the measurement system.

S = Qi

QO

Qo,L = S Qi + Z0

1) Calibration curve represents the characteristics of the measurement system. It can be written in the form

Linear function





3) Range is the difference between the maximum and the minimum values.

Input operating range, ri = Qi, max – Qi, min

Output operating range, ro = Qo, max – Qo, minFull-Scale-Operating range (FSO)



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4) Zero offset, Z0 is the deviation measured at the intercept with the ordinate.

eL(Qi) = Qo(Qi) – Qo,L(Qi)

Maximum error as a percentage of FSO range is calculated from

%eL,max = eL,max x 100 ro

5) Linearity error is the difference between the measured value and the value obtained from the calibration curve.





6) Resolution is the ability of the measurement system to detect and indicate small changes in the characteristic of the measurement result.

the smallest least significant digit the smallest scale increment

0.001 kg0.01 C



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7) Accuracy and Error

Accuracy of a measurement refers to the closeness of agreement between the measured value and the true value.

Error is defined as the difference between the measured value and the true value.

True value = the exact value of a variableMeasured value = The value of the variable indicated by a measurement system

Error, e = measured value – true value

Relative error, er = |measured value – true value| / true value x 100%




True value Measured value

Accuracy and Precision

Accurate but not precise(random error)

Precise but not accurate(systematic error)



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Accuracy and Precision (cont.)

Precision is sometimes stratified into:

Repeatability — the variation arising when all efforts are made to keep

conditions constant by using the same instrument and operator, and

repeating during a short time period.

Reproducibility — the variation arising using the same measurement

process among different instruments and operators, and over longer time

periods.




Significant figures

In any measurement, the number of significant figures is critical and refers to the number of digits that carry meaning contributing to its precision. It is equal to the number of digits that are known with some degree of confidence plus the last digit which is an estimate.

For example, 2.402 has four significant digits;

the first three digits (2, 4, 0) are known for sure but

the last digit (2) is estimated.



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Significant figures (cont.)

Rules for counting significant figures1) Leading zeros are not significant.

(e.g. 00042 => 2 significant digits)2) Zeros within a number are always significant.

(e.g. 00402 => 3 significant digits)3) Trailing zeros that aren’t needed to hold the decimal point are

significant. (e.g. 042.00 => 4 significant digits)4) Zeros that do nothing but set the decimal point are not

significant. (e.g. 42,000 => 2 significant digits)





A rule of thumb: reading the scale to 1/10 of the smallest division.

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30

20

The smallest division is 1 unit, so we can read the scale to ± 1/10 of 1 unit or ± 0.1 unit. Therefore, the value we read from the scale is 31.6 ± 0.1 unit.

We have 3 significant digits of which the “3” and the “1” are known for sure and the “6” is estimated.



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Significant Digits in Addition and Subtraction

When quantities are being added or subtracted, the number of decimal places (not significant digits) in the answer should be the same as the least number of decimal places in any of the numbers being added or subtracted.

Example:5.67 J (two decimal places)1.1 J (one decimal place)0.9378 J (four decimal place)7.7078 J (one decimal place)





Significant Digits in Multiplication, Division, Trig. functions, etc.

In a calculation involving multiplication, division, trigonometric functions, etc., the number of significant digits in an answer should equal the least number of significant digits in any one of the numbers being multiplied, divided etc.

Example: In evaluating sin(kx), where k = 0.097 m-1 (two significant digits) and

x = 4.73 m (three significant digits), sin (kx) = 0.44288 (the answer should have two significant digits).

Note that whole numbers have essentially an unlimited number of significant digits. As an example, if a hair dryer uses 1.2 kW of power, then 2 identical hairdryers use 2.4 kW:1.2 kW {2 sig. dig.} ´ 2 {unlimited sig. dig.} = 2.4 kW {2 sig. dig.}



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Instrument error

1. Hysteresis error

2. Linearity error

3. Sensitivity error

4. Zero-shift error

5. Repeatability error

Sensitivityerror

Actual

Expected

Linearity errorActual

Expected

Upscale

Downscale

Hysteresis

Occur in the ferromagnetic material or the deformation of some materials




Instrument error

Zero-shifterror

Actual

Expected

Data scatter band

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22 ⋯ 2Overall error,



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Dual sensitivity errors

is the error that occurs in the instrument due to the effect of other parameters

other than that of the primary parameter

Anticipated

Non-controlled environment

Actual

Zerodrift

Totalerror

Sensitivity change

Controlled environment

Anticipated response




Example of dual sensitivity errors

If a transducer is employed to measure some quantity (say, pressure) in

the process, and if the temperature also changes as the measurement is

made, error will result in the dual sensitivity of the transducer.

Primary quantity(pressure)

Secondary quantity(Temperature)

Zero offset

Sensitivity error

Dual sensitivity



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Example: Thermocouple calibration curves

Output

InputZero-offset

Sensitivity

Non-linearity




When a measurement system is calibrated, its indicated value is compared directly with a reference value. This reference value forms the basis of the comparison and is known as the standard. This standard may be based on the output

(1) from a piece of equipment,

(2) from an object having a well-defined physical attribute to be

used as a comparison, or

(3) from a well-accepted technique know to produce reliable value.

Standards

Primary standard > Secondary standard > Working standard



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Standards

1 meter

Platinum-Iridium meter bar

defined as the length of the path travelled by light in a vacuum in 1⁄299,792,458 of a second

1 kilogram

Platinum-Iridium weight

defined as being equal to the mass of the international prototype kilogram which is almost exactly equal to the mass of one liter of water at 4 C




Dimensions and Units

A dimension defines a physical quantity that is used to describe some aspect of a physical system, e.g. mass, length, time, etc.

A unit defines a quantitative measure of a dimension

For example: If we want to measure a distance (length), then its dimension is the L which has a unit of meter (for SI system)

Physical quantity Dimension Unit

Distance, Length L meter



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Base dimensions in the SI system

Physical quantity Dimension Unit Unit symbol

Length L meter m

Mass M kilogram kg

Time T second s

Temperature Kevin K

Current I ampere A

Amount of substance N mole mol

Luminous intensity J candela cd




Dimension SI unit Imperial unit Conversion

L m ft 1ft = 0.3048 m1 in = 0.0254 m

M kg lbm 1lbm = 0.45359 kg

T s s -

K C

RF

R = 1.8 KF = 1.8 C +32

Unit systems

SI units Imperial units



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Derived units

Other dimensions and their associated units are defined in terms of and derived from the base dimensions and units

L

m

T

s

divided by

equal

a

m/s2

divided by

equal

F

Kg. m/s2 = N

multiplied by

equal

V

m/s

T

s

M

kg




Derive quantity Derive unit Symbol

Area Square meter m2

Volume Cubic meter m3

Speed Meter per second m/s

Pressure, Stress Pascal Pa

Work, energy, or heat Joule J

Force Newton N

Power Watt W

Voltage Volt V

Resistance Ohm

Derived units



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Question #1

For the temperature calibration data as shown in table below, plot the result and determine the static sensitivity of the transducer.

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Resistance (Ohm) Temperature (C)

307 200.2

314 230.1

321 259.8

328 289.5

335 320.2

342 350.1

349 379.5

Question #2

The temperature of the water in the boiling process needs to be monitored. It is known that the temperature should be in the range as shown in the figure. If there are three temperature transducers available, which transducer would you select for this purpose? Explain.

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AB

C

Output [mV]

Input [°C]

Range


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Question #3

Determine the relative error that may occur if the actual sensitivity of an instrument is S1 but the anticipated (manufacturer) sensitivity is S2.

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AU 351 Sensors Technology in Automotive …charnnarong.me.engr.tu.ac.th/charnnarong/My classes/AU351...ความรพ นฐานเก ยวกบการว ด 7 คณะว