electronic instrumentation...

ELECTRONIC

INSTRUMENTATION

SYSTEM

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

Electronic Instrumentation System

Introduction

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


Quantity

The Electronic Instrumentation

System


Power supply Transducer

Conditioning

circuit

Amplifier

Recorder Data

processor

Engineering

analysis



Conditioning

circuit

Amplifier

Recorder Data

processor

Engineering

analysis

Power supply provides the energy to drive

the 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. Δ strain --- Δ resistance



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. Δ resistance --- Δ voltage using a

Wheatstone bridge



Conditioning

circuit

Amplifier

Recorder Data

processor

Engineering

analysis

Amplifiers are required in the system when

the voltage output from the transducer-signal

conditioner combination is small.

Amplifier with gains of 10 to 1000 are used to

increase these signals to levels (1-10 V) that

are compatible with the voltage-measuring

devices used in the system.



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).



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 representing the measurement in a

digital code. The output from the processor

is displayed in graphs or tables. Example:

computer.



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.


Power supply

Transducer

Conditioning

circuit Amplifier

Recorder

Data

processor

The electronic

instrumentation

system to

measure cutting

torque


Power supply

Thermocouple

Amplifier

Recorder

Data

processor

The electronic

instrumentation

system to

measure

temperature

CHARACTERISTICS AND

ERROR

Gambaran proses pengukuran

Menghasilkan Informasi

(Perubahan variabel-variabel)

Pengamat: orang yang

memerlukan informasi

Menghubungkan antara proses dan pengamat,

mengubah sinyal menjadi yang dapat terbaca oleh

pengamat dengan standar unit tertentu

Nilai sebenarnya dari variabel

proses

Nilai terukur (hasil pengukuran)

Static characteristics

These characteristics are used to define the performance criteria for the measurement of quantities that remain constant.

Dynamic characteristics

These characteristics are concerned with the relationship between the system input and output when the measured quantity is varying rapidly.

Characteristics of Measurement Systems


Karakteristik Sistem

Pengukuran

Accuracy

It is the difference between the measured and the true value of a quantity.

When a meter is said to be accurate to 1%, this means that a reading taken anywhere along one of its scales will not be in error by more than 1% of the full scale.

Sensitivity (a scale factor)

This is the relationship between a change in the output reading for a given change of the input. An instrument with a large sensitivity will indicate a large movement of the indicator for a small input change.

Linearity

The instrument is linear when incremental changes in the input and output are constant over the specified range.


Static Characteristics

Example:

An ammeter is specified as being accurate to 0.1% of its full- scale reading. If the 50 mA scale is used to measure currents of (a) 20 mA and (b) 40 mA, what is the error in the readings?

Solution:

Error = 0.1% x 50 mA = ± 0.5 mA at all readings

% error = ((measured value – true value) / (true value)) x100%

% error for 20 mA reading:

% error = ((20 ± 0.5) – 20) / (20)) x 100% = ± 0.25%

% error for 40 mA reading:

% error = ((40 ± 0.5) – 40) / (40)) x 100% = ± 0.125%

The higher the reading the smaller the error. Therefore, always use the smaller possible range when making reading with an analog meter.


Resolution

It is defined as the smallest input increment change that gives some small but definite numerical change in the output.

Threshold

If the instrument input is very gradually increased from zero there will be a minimum value required to give a detectable output change. This minimum value defines the threshold of the instrument.

Repeatability

The ability of measuring instrument to give identical indication, or response, for repeated application of the same value of the measurand under stated condition of use.



Hysteresis

This is the algebraic difference between the average errors at corresponding points of measurement when approached from opposite direction, i.e. increasing as opposed to decreasing values of the input.

Drift

This is variation in the output of an instrument which is not caused by any change in the input; it is commonly caused by internal temperature changes and component instability.

Zero stability

A measure of the ability of the instrument to return to zero reading after the measurand has returned to zero and other variations such as temperature, pressure, etc. have been removed.



Dead band

This is the largest change in the measurand to which the instrument does not respond. It is produced by friction, backlash or hysteresis in the instrument.

Readability

This is defined as the ease with which readings may be taken with an instrument.

Range

The scale range is defined as the difference between the nominal values of the measurand quantities corresponding to the terminal scale marks. It is expressed in the form ‘A’ to ‘B’ where A is the minimum scale value and B the maximum scale value.

The instrument range is the total range of values which an instrument capable of measuring. In a single range instrument this corresponds to the scale range.



Error of measurement: the difference between the absolute true value and the result of a measurement of quantity such as temperature, displacement, etc.

Well-designed electronic instrumentation systems limit the error.

Causes of errors:

- Accumulation of accepted error in each element.

- Improper functioning of any element in the system.

- Effect of the transducer on the process.

- Dual sensitivity of the transducer.

- Other less obvious sources.

Errors

Errors of Measurement

2. KESALAHAN BISA TIMBUL SBG AKIBAT DARI :

Akumulasi dari kesalahan yang diterima dari

setiap elemen pada sistem pengukuran

Adanya elemen dari sistem pengukuran yang

tidak berfungsi secara semestinya

Efek transduser pada proses

Sensitivitas ganda dari transduser

Beberapa sumber kesalahan lainnya

AKUMULASI DARI KESALAHAN

YANG DITERIMA

INSTRUMEN YANG TIDAK BERFUNGSI

DENGAN SEMESTINYA

EFEK TRANSDUSER PADA PROSES

Transduser harus dipilih dan ditempatkan

pada proses yang tidak mengganggu jalan

proses pengukuran. Untuk itu transduser

harus kecil dan ringan dari komponen yang

diamati, karena transduser mengambil

sedikit tenaga dari proses.

DUAL SENSITIVITY EROR

Transduser biasanya didisain untuk

mengukur kuantitas tunggal.

Ex : Tekanan/Suhu

Tapi transduser juga bisa sensitif terhadap

lebih dari satu kuantitas seperti transduser

tekanan yang digunakan berpengaruh

terhadap gaya dan suhu. Hal ini akan

mengakibatkan dual sensitivitas eror.

KESALAHAN LAIN

Efek kabel

Elektronik noise

Kesalahan operator

PROSEDUR UTK MEMINIMUMKAN KESALAHAN

DLM SISTEM PENGUKURAN

Memilih transduser secara hati-hati dengan mempertimbangkan berat, kebutuhan energi sehingga tidak mengganggu proses

Memeriksa akurasi setiap elemen dan memimimumkan kesalahan

Melakukan kalibrasi setiap instrumen

Mengamati dengan seksama proses dan lingkungan dimana proses pengukuran akan dilakukan

Variasi suhu dihindari sehingga tidak tejadi dual sensitivitas eror dengan menghubungakan sistem dengan kabel pembungkus dengan rapi

Hindari elektronik noise dengan menggunakan filter dan penutup

Periksa kesalahan total dari sistem untuk sumber input yang dipakai

Error of quantity: the difference between the specified quantity and the measured quantity without reference to any uncertainty in the measurement.

The uncertainty: the range within which the true value of the quantity measured is likely to lie at a given level of probability.

Example:

Specified shaft diameter = 40.00 mm

Result of measurement = 40.10 mm

Absolute error = result of measurement – specified size

= 40.10 mm – 40.00 mm

= + 0.10 mm

Relative error = (absolute error) / (specified size)

= + 0.10 / 40.00

= 0.0025 or 0.25%

Errors

Errors of Quantity

Method of elimination or reduction:

Careful attention to detail when making measurements.

Awareness of instrument limitations.

Use two or more observers to take critical data.

Taking at least three readings to reduce possible occurrence of gross

errors

Be motivated to the importance of correct results

Measurement Errors: how to estimate, reduce, or eliminate them

Human errors

Examples:

Misreading instrument, erroneous calculations,

improper choice of instrument, incorrect

adjustment, or forgetting to zero, neglect of

loading effects

Not possible to estimate their value mathematically


Careful calibration of instruments

Inspection of equipment to insure proper operation

Applying correction factors after finding instrument error.

Use more than one method of measuring parameter

System errors

Examples: bearing friction, calibration error, damaged equipment, loss

during transmission

How to estimate: compare with more accurate standard, determine if error is

a constant or proportional error

Equipment errors

Errors


Seal equipment and components under test

Maintain constant temperature and humidity by air conditioning

Shield component and equipment against stray magnetic fields

Use of equipment that is not effected greatly by environmental changes

System errors

Examples: Change in temperature, humidity, stray electric and magnetic field

How to estimate: careful monitoring of changes in the variables and

Calculating expected changes

Environmental errors

Errors


Careful design of measurement apparatus to reduce unwanted interface

Use of statistical evaluation to determine best true estimate of

measurement readings

Random errors

Example: unknown events that cause small variations in measurement

How to estimate: take many readings and apply statistical analysis to

Unexpected variations

Errors

The following quantities can be calculated using statistics:

Average or mean value of a set of measurements

Deviation from the average value

Standard deviation

Probability of error size in one observation

Statistical Evaluation of Measurement Data and Errors

Sample mean:

n = sample size

Deviation from the average value:

n

x

x

n

i

i 1

xxd i


Sample variance (σ2):

It is the average of the squared deviations from the mean

1

)(1

2

2

n

xxn

i

i

Sample standard deviation (s):

It is the most generally useful measure of variance; where s

is expressed in the same unit as the observations.

The probable error, r, that will occur if only one

measurement is taken:

r = ± 0.675 σ

1

)(1

2

n

xxn

i

i


The most important factor in the performance of a measuring system is that the full effect of an input signal (i.e. change in measured quantity) is not immediately shown at the output but is subject to some delay in response. It is known as measurement lag.

System Response

System Response

For a zero order system the equation is:

y(t) = K F(t)

where K is the static sensitivity or steady state gain.

The output, y(t), exactly follows the input forcing function, F(t), in time and that y(t) is amplified by a factor, K.

In fact, instrument manufacturers often provide values for the steady-state gains of their instruments. These values are obtained by performing static calibration experiments.

System Response

Zero Order Systems

Y

F

K = slope

Many measuring elements or systems can be represented by a first order differential equation (i.e. dx/dt, dy/dx, etc.)

Example of the first order transducers is mercury in glass thermometer or thermocouple which is used in temperature measurement.

Consider a thermometer initially at room temperature that is immersed into hot water. The temperature of hot water is represented by the following equation:

Thw is temperature of hot water; T, m, and CV are temperature, mass, and specific heat at constant volume of mercury; t is time

System Response

First Order Systems

dt

dT

hA

mCTT v

hw

Instruments with a moving elements controlled by a spring and probably fitted with some damping device are of second order type. These instruments are represented by a second order differential equation (d2x/dt2, d2y/dx2).

For a mass supported by a spring and a shock absorber, the input force applied to the system or the forcing function F(t):

m = mass, y = vertical displacement, k = spring constant, γ = the damping coefficient, t = time

System Response

Second Order Systems

yd

d

kd

d

k

mtF

k t

y

t

y

2

2

)(1

KARAKTERISTIK STATIK SISTEM

PENGUKURAN

Karakteristik Statik Sistem

Pengukuran

Resolusi, Stabilitas dan

Sensitivitas

Karakteristik Statik Sistem

Pengukuran

Linearitas dan Non Linearitas

Contoh

Error Reduction Techniques

Karakteristik Dinamik Sistem

Pengukuran

Kalibrasi

• Kalibrasi - membandingkan alat ukur dgn referensi

Kalibrasi

BASIC ELECTRONICS:

OVERVIEW

In the design and application of an instrument system a number of analog and digital circuits are used.

This chapter contains a review of the basic electronics concepts and laws that are useful in using and understanding modern instrumentation systems.

Concepts and Definitions

Quantity Symbol Units Abbrev. Alternate

Charge q coulomb C (A.s)

Current I ampere A (C/s)

Voltage v volt V (W/A)

Electric force Fe newton N

Electric field E joule J (N.m)

Electric potential Φ Joule/coulomb J/C

Charge (q) the integral of the current with respect to time.

A charge of 1 C is transferred in 1 s by a current of 1 A

Current (I) The amount of charge that moves per unit time through or between materials.

By convention, current is considered to flow from the anode (+) to the cathode (-)

Concept and Definitions

t

dtiq0

.

dt

dqi

Electric Force (Fe) The electric force acting between the charges on the bodies:

Where: K = 1/(4o), o= 8.854187817 x 10-12, q1, q2 = charges of the two bodies, R = distance between the bodies. F in N

Electric Field (E)

E in N/C.

The work required to move a charge of 1 C through a unit electric field of 1 N/C a distance of 1 m is 1 J.


2

21..

R

qqkFe

q

FE e

Electric Potential (Φ) The electric field potential energy per unit charge. Electric potential is in J/C or V.

Electric Resistance (R) and Resistivity (ρ)

R = resistance in Ω, ρ = resistivity in Ω.m, L = length of wire in m, A = cross sectional area of wire in m2.

It is related to the temperature of the material (T) and coefficient of thermal expansion ()


A

LR

)](1[

)](1[

oo

oo

TTRR

TT

Electric Power (P)

P in J/s or W

Electric Capacitance (C)

Capacitance is in coulombs per volt or in the farad (F).

Electric Inductance (L) L = Φ/I

L is in the henry (H)


VqC /

RiP

ViP

2

.

Circuit Elements

Resistor

Capacitor

Transistor

Inductor

Voltage source

Current source

SENSOR AND SIGNAL

CONDITIONING

DEFINITION

STRAIN

GAGES:

…………………………………………………………….

TRANSDUCER:

……………………………………

Thin metal foil grids that can be

adhesively to the surface of

a component or structure.

Electromechanical devices that convert a mechanical change,

such as displacement or force, into a change in an electrical

signal that can be monitored as voltage after conditioning.

Torque, moment or

moment of force, is the

tendency of a force to

rotate an object about an

axis. Just as a force is a

push or a pull, a torque

can be thought of as a

twist.

Any influence that

causes an object to

undergo a change in

speed, a change in

direction, or a

change in shape.

STRAIN GAGES

To identify the strain gages

applications in transducers for

force measurements

1 Automotive Auto test measure devices: pedal, shifting, multi

axial

2 Bending Beam Measures force, pressure, and displacement

3 Column/Canister Conventional and miniature column designs for

compression measurement

4 Donut Tension or compression, designed for space limited

clamp force measurement

5 Fold Back Beam Compact precision bending beams designed for

original equipment manufacturers applications

6 Force Sensor

Economical original equipment manufacturers

bending beam designed for force, pressure, and

displacement

7 Load/Force Washer Compact hollow design for fastener clamp force

measurement

8 Load Button Compression only designed for space limited

applications

9 Medical Related Rehab force measurements, original equipment

manufacturers bending beams, multi axis sensors

10 Overload

Protection

Designed to help protect sensors from accidental

and or excess forces

11 Pancake Low profile, high precision, tension or compression

Load Cell

12 S Beam/ Z beam Inline Load Cell, primarily for tension measurement

13 Thread female

mount

Various tension or compression internal thread

mount Load Cell

14 Thread male mount Various tension or compression stud mount

threaded Load Cell

15 Thru hole Tension or compression, designed for space limiting

clamp force measurement

Selection of Load Cells can be

categorized by the following styles:

VARIOUS EXAMPLES OF STRAINS GAGES APPLICATIONS

IN TRANSDUCERS FOR FORCE MEASUREMENTS

Car Door Test Bag Filling Machine Tank Dispensing

Wind Tower Suspension Bridge Tank / Silo / Hopper

Viscosity / Liquid

Separation

Assembly line /

Automation

Dual Tank Level

Controller

Closed Loop Feedback Wireless Shoe Sensor Snow Shoe Test

Hydraulic Press Miniature Load Cell Medical Bag

Food Packaging Batch Weighing Mass Flow Meter

Biometric Windsurf Crane Weighing

Bite Force Application

for Dementia Study

Tube Expansion

Measurement Musculoskeletal Testing

Force Testing /

Material Testing /

Concrete Crush Test

Wire Tension /

Compression

Measurement

Bolt Fastening /

Clamping

Measurement

Pedal Force Testing Press

Dual Tank Level Controller Bag Filling Machine Tank Dispensing Wind Tower Tank / Silo / Hopper Viscosity / Liquid Separation Assembly line / Automation Miniature Load Cell Food Packaging

http://www.futek.com/product.aspx?t=load&cat=th&m=lth400

http://www.futek.com/product.aspx?t=load&cat=cf&m=lcf555


http://www.futek.com/product.aspx?t=instrument&cat=bt&m=ibt500

http://www.futek.com/product.aspx?t=instrument&cat=pm&m=ipm600

http://www.futek.com/product.aspx?t=load&cat=sb&m=lsb302



http://www.futek.com/product.aspx?t=instrument&m=ipm500


http://www.futek.com/product.aspx?t=load&m=lcf400

http://www.futek.com/product.aspx?t=load&cat=sb&m=lcf650



http://www.futek.com/product.aspx?t=load&m=LLW450




http://www.futek.com/product.aspx?stock=FSH02126&acc2=acc




http://www.futek.com/product.aspx?t=load&cat=cf&m=LCF550

http://www.futek.com/product.aspx?t=load&cat=cf&m=LCF700


http://www.futek.com/product.aspx?t=load&cat=rf&m=lrf400


http://www.futek.com/product.aspx?t=load&m=llb500


http://www.futek.com/product.aspx?t=load&cat=cb&m=lcb500

http://www.futek.com/product.aspx?t=load&cat=th&m=lth500





http://www.futek.com/product.aspx?t=load&m=lsm250

http://www.futek.com/product.aspx?t=load&m=lsm300

http://www.futek.com/product.aspx?t=instrument&m=csg110

STRAIN GAGES



torque measurements

1 Air Tool Reaction Designed as an integral part of nut-runner for

automation assembly

2 Flange to Flange

Reaction Flange mounted reaction Torque Sensor

3 Hex Drive Rotary

Slip ring and non-contact rotary torque

measurement for in-line application and

available with encoders

4 Screw driver reaction Used in low torque fastener torque auditing

assembly

5 Shaft to Shaft Rotary


measurement for in-line application and

available with encoders

6 Shaft to Shaft Reaction Shaft mounted reaction torque transducers

7 Square Drive Rotary


measurement for in-line application, available

with encoders

8 Square Drive to Flange

Reaction

Designed for auditing torque measuring devises

and fastener auditing tools

9 Square Drive to Square

Drive Reaction

Female square drive mounted reaction torque

transducers

10 Torque Wrench

Reaction Commonly used for fastener torque auditing

Selection of Torque Cells can be

categorized by the following styles:

VARIOUS EXAMPLES OF STRAINS GAGES

APPLICATIONS IN TRANSDUCERS FOR

TORQUE MEASUREMENTS

Precision &

Maintenance

Assembly Line

/ Automation

Reaction

Torque Sensor

Peristaltic

Pump

Prosthetic

Limbs

Torque

Verification

Break Torque /

Peak Torque

Motor Test

Stand

Torque

Screwdriver

Rotating Torque

Monitoring

System

ROTATING TORQUE

MONITORING

SYSTEM

ASSEMBLY LINE /

AUTOMATION

REACTION TORQUE

SENSOR

BREAK TORQUE /

PEAK TORQUE

MOTOR TEST

STAND

PRECISION &

MAINTENANCE 1 2 3 4 5 6

http://www.futek.com/product.aspx?t=torque&m=TRS300




http://www.futek.com/product.aspx?t=torque&m=TFF500




http://www.futek.com/product.aspx?t=torque&m=tff325






http://www.futek.com/product.aspx?t=instrument&m=usb210

http://www.futek.com/product.aspx?t=torque&m=trs605

http://www.futek.com/product.aspx?t=torque&m=trs705



STRAIN GAGES



combination of force and torque

measurements

http://www.futek.com/product.aspx?t=load&m=LCF400

http://www.futek.com/product.aspx?t=load&m=LCF450

http://www.futek.com/product.aspx?t=load&m=LTH500



Load Cells and torque cell,

utilizing one of the

most advanced technologies

in the Sensor Industry.

There are many

other applications other

than describe before

in force and torque

measurements

electronic instrumentation...

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