Biosensors & Transducers: Measurement System

1. Measurement System
MUKESH SUNDARARAJAN

2. Contents:
2
▶ Introduction
▶ Order of Instruments
▶ Instruments Classification
▶ Units of Measurement
▶ Standards of Measurement
▶ Dimensions of Measurement
▶ Errors in Measurement
▶ Instrument Characteristics
▶ Calibration of Instruments
▶ References

3. Introduction:
▶ Instrumentation is that branch of engineering that primarily deals with sensing,
measurement and control.
▶ Electrical and electronic instrumentation deals with the electrical and electronic
instruments which are used for measurement.
▶ It is study of operation and functionality of instruments.
▶ Instrumentation is a technology for measurement.
▶ Use of measuring instruments depends up on the particular application.
▶ An instrument is defined as the device or the system which is designed in such a way
that it maintains the functional relationship between a prescribed property of a
substance and a physical variable, and communicates this relationship to a human
observer by some ways and means.
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4. Introduction:
▶ Measurement is made for the following purpose:
1. To monitor process and operation.
2. To control process and operation.
3. To carry out some analysis.
▶ Monitoring: All instruments indicate a particular quantity. These are called readings of
particular system. In normal sense, readings do not perform controlling. It is made for
monitoring purpose.
▶ Controlling: In case after reading, if we want to change the value of output then we
control our instruments. For example when one measures body temperature (fever) and
it is not normal then we control this particular temperature and want to get it normal
applying medication.
▶ Analysis: Prediction and original value of output comes in to analysis.
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5. Characteristics of instruments can be divided into two types:
▶ Desirable
1. Accuracy
2. Sensitivity
3. Reproducibility
▶ Undesirable
1. Drift
2. Dead zone - Hysteresis
i. Threshold
ii. Resolution
3. Static error
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6. ▶ For the result to be meaningful, there are two basic requirements:
1. The comparison standard is accurately defined and commonly accepted.
2. The procedure and the instrument used for obtaining the comparison must be provable.
An electronic instrument is one which is based on electronic or electrical principles for its
measurement function.
The measurement of any electronic or electrical quantity or variable is termed as an
electronic measurement provided it gives digitized output.
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7. ▶ Favorable conditions for Electronic Measurement are:
1. Most of the quantities can be transduced in to the electrical or electronic signals.
2. An electronic or electrical signal can be amplified, filtered, multiplexed, sampled and
measured.
3. The measurement can easily be obtained and converted into some digital form for
automatic analysis and recording.
4. The measured signals can be transmitted over long distances with the help of cable, radio
links, wireless communication etc.
5. Many measurements can be carried either simultaneously or successively.
6. Electronic circuits can detect and amplify very weak signals and can measure the events of
very short duration as well.
7. Electronic measurement can build analog and digital signals.
8. Higher sensitivity, low power consumption and higher degree of reliability are the
important features of electronic instruments and measurements.
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8. Order of Instruments:
▶ Order of a System: The order of the system is defined by the number of independent
energy storage elements present in the system, and intuitively by the highest order of
the linear differential equation that describes the system. In a transfer function
representation, the order is the highest exponent in the transfer function.
▶ Zero Order: This is the response often desired in instruments because it means that
the block does not alter the time response. All instruments behave as zero order
instruments when they give a static output in response to a static input.
 Example: Wire Strain Gauge.
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9. Order of Instruments:
▶ First Order: The system whose input-output equation is a first order differential
equation is called a first order system. The order of the differential equation is the
highest degree of derivative present in an equation. First order system contains only
one energy storing element.
 Example: Mass - Damper System; Mass Heating System.
▶ Second Order: A system whose input-output equation is a second order differential
equation is called a Second Order System. There are a number of factors that make
second order systems important. They are simple and exhibit oscillations and
overshoot.
 Example: Mass-Spring-Damper Systems and RLC Circuits.
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10. Instruments Classification: 12
▶ The instrument used for measuring the physical and electrical quantities is known as
the measuring instrument.
▶ The term measurement means the comparison between the two quantities of the same
unit.
▶ The magnitude of one of the quantity is unknown, and it is compared with the
predefined value.
▶ The result of the comparison is obtained in numerical value.
▶ The measuring instrument categorised into three types;
1. Electrical Instrument
2. Electronic Instrument
3. Mechanical Instrument

11. Instruments Classification: 2…
of 7
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12. 14
▶ The mechanical instrument is used for measuring the physical quantities. This
instrument is suitable for measuring the static and stable conditions because the
instrument is unable to give the response to the dynamic condition.
▶ The electronic instrument has quick response time. The instrument provides a quick
response as compared to the electrical and mechanical instrument.
▶ The electrical instrument is used for measuring electrical quantities like current,
voltage, power, etc., viz. ammeter, voltmeter, wattmeter.

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▶ Absolute Instrument gives the value of measured quantities regarding the physical
constant. The physical constant means the angle of deflection, degree and meter constant.
Mathematical calculations are required for knowing the value of a physical constant.
▶ The tangent galvanometer is an example of the absolute instruments. In tangent
galvanometer, the magnitude of current passing through the coil is determined by the
tangent of the angle of deflection of its coil, the horizontal component of the earth
magnetic field, radius and the number of turns of wire used.
▶ Secondary Instrument: The deflection shows the magnitude of the measurable
quantities. The calibration of these instruments with the standard instrument is essential
for the measurement. The output of this type of device is directly obtained, and no
mathematical calculation is required for knowing their value.

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▶ Digital Instrument gives the output in the numeric form. The instrument is more
accurate as compared to the analogue instrument because no human error occurs in the
reading.
▶ Analogue instrument is the instrument whose output varies continuously. The analogue
instrument has the pointer which shows the magnitude of the measurable quantities.
The analogue device is further classified into two types.
1. Null Type
2. Deflection Type

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▶ Null Type Instrument
In this instrument, the zero or null deflection indicates the magnitude of the measured
quantity. The instrument has high accuracy and sensitivity. In null deflection
instrument, one known and one unknown quantity are used. When the value of the
known and the unknown measuring quantities are equal, the pointer shows the zero or
null deflection. The null deflection instrument is used in the potentiometer and in
galvanometer for obtaining the null point.
▶ Deflection Type Instrument
The instrument in which the value of measuring quantity is determined through the
deflection of the pointer is known as the deflection type instrument. The measuring
quantity deflects the pointer of the moving system of the instrument which is fixed on
the calibrated scale. Thus, the magnitude of the measured quantity is known.

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▶ The deflection type instrument is further sub-classified into three types.
1. Indicating Instrument – The instrument which indicates the magnitude of the measured
quantity is known as the indicating instrument. The indicating instrument has the dial
which moves on the graduated scale. E.g., voltmeter, ammeter, power factor meter.
2. Integrating Instrument – The instrument which measures the total energy supplied at a
particular interval of time is known as the integrating instrument. The total energy
measured by the instrument is the product of the time and the measured electrical
quantities. E.g., energy meter, watt-hour meter.
3. Recording Instrument – The instrument that records the circuit condition at a particular
interval of time is known as the recording instrument. The moving system of the
recording instrument carries a pen which lightly touches on the paper sheet. The
movement of the coil is traced on the paper sheet. The curve drawn on the paper shows
the variation in the measurement of the electrical quantities.

17. Units of Measurement:
▶ Metrology is the science of developing nationally and internationally accepted units of
measurement.
▶ Aunit is any standard used for making comparisons in measurements.
▶ Unit conversions allow for measurements of a property that have been recorded using different
units
▶ The metric system is a framework of units of measurement that has grown from its 1874 birth
in a diplomatic treaty to the more modern General Conference on Weights and Measures, or
CGPM (Conferérence Générale des Poids et Measures).
▶ The modern system is properly called the International System of Units, or SI, an abbreviation
from the French Le Système International d'Unités.
▶ Today, most people use the names metric and SI interchangeably.
▶ The metric system is the main system of measurement units used in science.
▶ Each unit is considered to be dimensionally independent of the others.
▶ These dimensions are measurements of length, mass, time, electric current, temperature,
amount of a substance, and luminous intensity.
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18. Units of Measurement: 7 Base Metric Units
▶ Length: Meter (m) The meter is the metric unit of length. It is defined as the length of
the path light travels in a vacuum during 1/299,792,458th of a second.
▶ Mass: Kilogram (kg) The kilogram is the metric unit of mass. It is the mass of the
international prototype of the kilogram: a standard platinum/iridium 1 kg mass housed
near Paris at the International Bureau of Weights and Measures (BIPM).
▶ Time: Second (s) The basic unit of time is the second. The second is defined as the
duration of 9,192,631,770 oscillations of radiation corresponding to the transition
between the two hyperfine levels of cesium-133.
▶ Temperature: Kelvin (K) The Kelvin is the unit of thermodynamic temperature. It is the
fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The
Kelvin scale is an absolute scale, so there is no degree.
The triple point is the temperature and pressure at which solid, liquid, and vapour
phases of a particular substance coexist in equilibrium.
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19. ▶ Amount of a Substance: Mole (mol) The mole is defined as the amount of a substance
that contains as many entities as there are atoms in 0.012 kilograms of carbon-12.
When the mole unit is used, the entities must be specified. For example, the entities
may be atoms, molecules, ions, electrons, cows, houses, or anything else.
▶ Luminous Intensity: Candela (cd) The unit of luminous intensity, or light, is the
Candela. The candela is the luminous intensity, in a given direction, of a source
emitting monochromatic radiation of frequency 540 x 1012 hertz with radiant intensity
in that direction of 1/683 watt per steradian.
▶ Electric Current: Ampere (A) The basic unit of electric current is the ampere. The
ampere is defined as the constant current that, if maintained in two infinitely long
straight parallel conductors with a negligible circular cross-section and placed 1 m
apart in a vacuum, would produce a force between the conductors equal to 2 x 10-7
Newton per meter of length.
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20. Units of Measurement: Other Basic Units
▶ Liter (L) While the metric unit of volume is the cubic meter, 𝑚3, the most commonly
used unit is the liter. A liter is equal in volume to one cubic decimeter, 𝑚3, which is a
cube that is 0.1 m on each side.
▶ Angstrom (Å) One angstrom equals 10−8 cm or 10−10 m. Named after Anders Jonas
Ångstrom, the unit is used to measure the chemical bond length and electromagnetic
radiation wavelength.
▶ Cubic centimeter (𝑐𝑚3) A cubic centimeter is a common unit used to measure solid
volume. The corresponding unit for liquid volume is the milliliter (mL), which is equal to
one cubic centimeter.
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21. Units of Measurement: Derived Units
▶ The seven base units form the basis for derived units. Still more units are formed by
combining base and derived units.
1. Radian (rad): Unit used to quantify an angle. 𝑚. 𝑚−1
2. Hertz (Hz): Used for frequency. s−1
3. Newton (N): Unit of weight or force. kg⋅m⋅s−2
4. Joule (J): Unit of energy, heat, or work. kg⋅m2⋅s−2
5. Watt (W): Unit of power or radiant flux. kg⋅m2⋅s−3
6. Coulomb (C): Unit of electric charge. 𝑠. 𝐴
7. Volt (V): Unit of electric potential or voltage. kg⋅m2⋅s−3⋅A−1
8. Farad (F): Unit of capacitance. kg−1⋅m−2⋅s4⋅A2
9. Tesla (T): Metric unit of magnetic flux density. kg⋅s−2⋅A−1
10. Degree Celsius (°C): Temperature relative to 273.15 K.
11. Gray (Gy): Unit of absorbed radiation dose. m2⋅s−2
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22. Units of Measurement: Systems of Units
▶ A system of units is a set of related units that are used for calculations. The system
includes base units, which represent base dimensions, and derived units, which
represent products of powers of base dimensions.
1. SI (International System of Units) (meter-kilogram-second-ampere-kelvin-mole-
candela)
2. FPS (foot-pound-second)
3. MKS (meter-kilogram-second)
4. CGS (centimeter-gram-second)
5. EMU (Electromagnetic) (centimeter-gram-second-abampere)
6. ESU (Electrostatic) (centimeter-gram-second-abcoulomb)
7. Atomic (bohr-electron mass-atomic second-electron)
8. MTS (meter-tonne-second)
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23. Standards of Measurement:
▶ In metrology (the science of measurement), a standard (or etalon) is an object, system,
or experiment that bears a defined relationship to a unit of measurement of a physical
quantity.
▶ Standards are the fundamental reference for a system of weights and measures, against
which all other measuring devices are compared.
▶ There is a three-level hierarchy of physical measurement standards.
1. Primary Standards made to the highest metrological quality and are the definitive
definition or realization of their unit of measure.
2. Secondary Standards are very close approximations of primary reference standards
which are calibrated against the primary standards.
3. Working Standards are used for checking its measuring instruments used in industries
having a traceable relationship to the secondary and primary standards and they
deteriorate over time.
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24. Dimensions of Measurement:
▶ Dimensions of a physical quantity are the powers to which the fundamental quantities
must be raised to represent the given physical quantity.
▶ In mechanics, all physical quantities can be expressed in terms of mass (M), length (L)
and time (T).
▶ Dimensional measurement is how we know and quantify the size and shape of things.
▶ It involves lengths and angles as well as geometrical properties such as flatness and
straightness.
▶ Dimensional measurement is of fundamental importance for interchangeability and
global trade. It is how we ensure that things will fit together.
▶ Without global length standards as the basis for standardized parts globalized industry
would not be possible.
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25. Errors in Measurement:
▶ The measurement error is defined as the difference between the true or actual value
and the measured value.
▶ The true value is the average of the infinite number of measurements, and the
measured value is the precise value.
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26. Errors in Measurement – Types
▶ The gross error which occurs because of the human mistakes. It can only be avoided by
taking the reading carefully.
▶ Systematic Errors
1. Instrumental Errors (inherent, Misuse, Loading)
2. Environmental Errors
3. Observational Errors
▶ Random Errors which are caused by the sudden change in the atmospheric condition,
are called random error. These types of error remain even after the removal of the
systematic error. Hence this type of error is also called residual error.
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27. Errors in Measurement – Types
 Instrumental Error arises due to three main reasons:
1. Inherent Shortcomings of Instruments – Such types of errors are inbuilt in instruments
because of their mechanical structure.
2. Misuse of Instrument – The error occurs in the instrument because of the fault of the
operator. A good instrument used in an unintelligent way may give an enormous
result.
3. Loading Effect – It is the most common type of error which is caused by the
instrument while measuring. For example, when the voltmeter is connected to the
high resistance circuit it gives a misleading reading, and when it is connected to the
low resistance circuit, it gives the dependable reading. This means that the voltmeter
has a loading effect on the circuit.
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28. Errors in Measurement – Types
 Environmental Errors
▶ These errors are due to the external condition of the measuring devices. Such types of
errors mainly occur due to the effect of temperature, pressure, humidity, dust, vibration
or because of the magnetic or electrostatic field. The corrective measures employed to
eliminate or to reduce these undesirable effects are
1. The arrangement should be made to keep the conditions as constant as possible.
2. Using the equipment which is free from these effects.
3. By using the techniques which eliminate the effect of these disturbances.
4. By applying the computed corrections.
 Observational Errors
▶ Such types of errors are due to the wrong observation of the reading. There are many
sources of observational error. For example, the pointer of a voltmeter resets slightly
above the surface of the scale. Thus an error occurs (because of parallax) unless the line
of vision of the observer is exactly above the pointer. To minimise the parallax error
highly accurate meters are provided with mirrored scales.
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29. Errors in Measurement – Types 31

30. Instrument Characteristics:
InstrumentCharacteristicsallow users to select the most suitable instrumentfor specific measuring
jobs.
 ▶ There are two basic performance characteristics of measuring instrument:
1. Static Characteristics: value of the measured variable change slowly.
2. Dynamic Characteristics: value of the measured variable change very fast.
 ▶ The static characteristics and parameters of measuring
instruments describe the performance of the instruments related to the
steady-state input/output variables only.
The various static characteristics and parameters are destined for quantitative
description of the instrument.
▶ Dynamic characteristic shows the time response behavior of the instrument to the changes in the
magnitude of interest by observing the signal output with time.
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31. Static Characteristics:
1. Accuracy: Closeness of a measurement to the true value.
2. Precision: Closeness of agreement among a set of results.
3. Sensitivity: Increment of the output signal (or response) to the increment of the input
measured signal.
4. Repeatability: Variation in measurements taken on the same item under the same
conditions.
5. Reproducibility: Ability of a measurement to be duplicated, either by the same person
or by someone else under changed conditions.
6. Drift: Change in instrument output over time - when the true value is constant.
7. Resolution: Minimum change in input that is required for change in output.
8. Threshold: The minimum limit of the input reading.
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32. Static Characteristics:
9. Range: Input range of a measuring device specified by the minimum and maximum
values of input variable.
10. Span: Difference between the maximum and the minimum values of input variables.
11. Linearity: Maximum deviation from linear relation between input and output.
12. Error: Deviation of the true value from the desired value.
13. Hysteresis: When unloading applied input do not create the same output.
14. Creep: Time an instrument needs to adapt to change in applied input.
15. Trueness: Closeness of the mean of a set of measurement results to the actual (true)
value.
16. Calibration:
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33. Dynamic Characteristics:
▶ Speed of response
▶ Dynamic Error: The difference between the true and measured value with no static
error.
▶ Lag: Response delay
▶ Fidelity: The degree to which an instrument indicates the changes in the measured
variable without dynamic error (faithful reproduction).
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34. Calibration & Traceability of Instruments:
▶ Calibration is a comparison between a known measurement (the standard) and the
measurement carried out using another instrument.
▶ Calibration is the way that the standards are transferred from one country to another, and from
one instrument to another.
▶ The primary reference standards for the SI units of measurement are held in France and each
country compares their national standards against these.
▶ Calibration of measuring instruments has three objectives.
1. Checking for the accuracy of the instrument.
2. Determining the traceability of the measurement.
3. Repairing of the device if it is out of calibration.
▶ Measurement traceability is used to refer to an unbroken chain of comparisons relating an
instrument's measurements to a known standard.
▶ Traceability of instruments is used to determine its bias, accuracy and precision.
▶ A traceable measurement is one which has an unbroken chain of calibrations going back to the
primary reference standard, with uncertainties calculated for each calibration.
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35. THANK YOU