Measurement Sensors Devices -...

Measurement Sensors Devices

Jiří Tůma

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Mechanical clock An escapement is a device in mechanical watches and clocks that transfers energy to the timekeeping element (the "impulse action") and allows the number of its oscillations to be counted (the "locking action").

Verge escapement showing (c) crown wheel, (v) verge, (p,q) pallets. The verge probably evolved from the mechanism to ring a bell. There has been speculation that Villard de Honnecourt invented the verge escapement in 1237.

The second verge pendulum clock built by Christian Huygens, inventor of the pendulum clock, 1673. Huygens claimed an accuracy of 10 seconds per day.

2 (C) Jiří Tůma, 2016

//upload.wikimedia.org/wikipedia/commons/e/ee/Scappamento.gif

//upload.wikimedia.org/wikipedia/commons/a/a3/Verge_Escapement_Labelled.png

Measurement systems

Input Sensor

Output

Physical quantity: Displacement, speed, RPM, acceleration, pressure, temperature, force, flow rate, ……

Signal in observable form: Voltage, electric current, pressure, digital Signal type: Binary (true/false), (log 0/log 1), (low/high) Analog (0 to 10 V, -5V to +5V, 4 to 20 mA) Digital


A transducer is a device that converts one form of energy to another form of energy. The term transducer commonly implies sensor or detector or probe. Transducers are widely used in measuring instruments.

Block diagrams

System Input Output

S1 An input of S1

S2 An output of S1

An input of S2

An output of S2

The output of the System S1 becomes the input of the system S2

tx

ty

tytxtz tx

ty

tytxtz

tx ty

tx ty tz

Special blocks for adding and subtracting a pair of signals

Block Diagrams are a useful and simple method for analyzing a system

S1 ty1

S2 ty2

tx1

tx2

tytyty 21 S1

ty txS2

tz

Serial connection

Parallel connection


Feedback loops

S1 ty tx

S2

5

Positive feedback

tw

tz

+

+ S1

ty tx

S2

Negative feedback

tw

tz

+

-

Feedback signal Feedback signal

Self-regulating mechanisms have existed since antiquity, and the idea of feedback had started to enter economic theory in Britain by the eighteenth century, but it wasn't at that time recognized as a universal abstraction and so didn't have a name. The verb phrase "to feed back", in the sense of returning to an earlier position in a mechanical process, was in use in the US by the 1860s, and in 1909, Nobel laureate Karl Ferdinand Braun used the term "feed-back" as a noun to refer to (undesired) coupling between components of an electronic circuit. By the end of 1912, researchers using early electronic amplifiers (audions) had discovered that deliberately coupling part of the output signal back to the input circuit would boost the amplification (through regeneration), but would also cause the audion to howl or sing. This action of feeding back of the signal from output to input gave rise to the use of the term "feedback" as a distinct word by 1920. [http://en.wikipedia.org/wiki/Feedback_control]

(C) Jiří Tůma, 2016

Use of sensors or transducers in measurements (in general) In nature (chemical sensors, biosensors) in control systems, in diagnosis (medical, machinery, buildings and bridges, etc.)


• Pressure sensor • Ultrasonic sensor • Humidity (amount of water vapor in the air) or water in bulk materials • Gas sensor (composition) • Passive infrared motion sensor (the presence of objects) • Acceleration sensor • Displacement sensor • Force measurement sensor • Color sensor • Gyro sensor • Temperature sensor • Flow rate sensor or measurement systems

Types of sensors

Control systems

Logic control Linear control


Analog controller Digital controller

Controllers Sensors Actuators

A controller is a device, historically using o mechanical, o hydraulic, o pneumatic o or electronic techniques often in combination, but more recently in the form of a microprocessor or computer

Watt steam engine

A late version of a Watt double-acting steam engine, in the lobby of the Superior Technical School of Industrial Engineers of the UPM (Madrid). Steam engines of this kind propelled the Industrial Revolution in Great Britain and the world

Improving on the design of the 1712 Newcomen engine, the Watt steam engine, developed sporadically from 1763 to 1775, was the next great step in the development of the steam engine.

Watt or fly-ball centrifugal governor

James Clerk Maxwell 1868

steam regulator valve


//upload.wikimedia.org/wikipedia/commons/9/9e/Maquina_vapor_Watt_ETSIIM.jpg

Mechanical controllers

Tank fill valve

feedback

Float

Lift arm

Flush valve

Flush toilet

Flush tube

weight

Cooking pot

valve

heating

Pressure regulator


http://en.wikipedia.org/wiki/File:Papin_cooking_pot_late_18th_century.jpg

http://en.wikipedia.org/wiki/File:DE_Toilette.JPG

A feedback control loop

(C) Jiří Tůma, 2016 10

Comparator

Controller operating

on error e = w - y

tu te

tw

ty

+

-

Feedback loop

tySystem to be controlled

(Plant)

Controller output Measured response Error ywe

twty

tv tv

Disturbance

Desired value

Objectives

Automatic control

Controller Actuator System (plant)

Sensor 1

Sensor 2

Disturbance

Reference System output

Controller

Feesback

CO … Controller Output, control variable, manipulated variable PV … Process Variable, controlled variable, measured variable SP … Set Point, desired value, reference signal, command e = SP – PV (error) measured error

SP e CO PV

Feed-forward Not be measured*)


*) Sensor is not available or the parameter is not measured by design

ISO 3511/1 versus textbooks

Fill valve

Control valve for draining

LCA 071

Level h hSP

H

Tank filled with liquid

S

Level of liquid h

Flow rate Qi

C

Flow rate Qo

hSP

Tank Controller

Feedback

Inflow

Drain

International standard ISO 3511/1 Process measurement control functions and instrumentation – Symbolic representation - Part 1: Basic requirements

Letter code for identification of instrument functions Example: LCA – Level, Control, Alarm, H-high

Textbooks on control theory - Analysis - Design

Closed loop for liquid level control


Piping and instrumentation diagrams


Point of measurement

Instrument (a devices or combination of devices used directly or indirectly to measure, display and/or control a variable)

Panel mounted instrument

Locally mounted instrument

Correcting unit (actuating and correcting elements which adjust the correcting conditions)

Actuating element (that part of the correcting unit which adjusts the correcting elements)

Correcting element (that part of the correcting unit which directly adjusts the value of the correcting conditions)

Alarm (a device which is intended to attract attention to a defined abnormal condition by means of a discrete audible and/or visible signal)

Set value (the value of the controlled condition to which the controller is set)

valve

H Integral manual Automatic Only manual H

H

valve general

general

(P&IDs)

Understanding the symbol system


Actuating element operation

- Control valve opens on failure of actuating energy

- Control valve opens on failure of actuating energy

- Control valve retains position on failure of actuating energy

Types of line

Instrument signal line

Direction of flowing information

Line used to delineate the plant

Position of function identifying letters

LCA

071

LCA

071

LCA

071

H

Instrument

Panel mounting instrument

Panel in control room

Local panel

Letter code Loop number

Crossing and junctions

(Alarm)

Letter code for identification of instrument functions


1 2 3 4 First letter Succeeding letter

Measured or initiating variable Modifier Display or output function

A Alarm B

C Controlling D Density Difference E All electric variables F Flow rate Ratio G Gauging, position or length H Hand (manually initiated) operated

I Indicating J Scan K Time or time programe L Level M Moisture or humidity N User’ choice O User’ choice P Pressure or vacuum Q Quality, for example

– analysis concentration conductivity

Integrate or totalize

Integrating or summating

R Nuclear radiation Recording

S Speed or frequency Switching

T Temperature Transmitting U Multivariable

V Viscosity

W Weight or force X Unclassified variables

Y User’ choice Z Emergency or safety acting

Process control


Flow rate Q2

Flow rate Q0

LCA 051

Level

Flow rate Q1

QIC 052

pH

FRQ 054

TIR 053

H

M A B

ISO 3511-1:1977, Process measurement control functions and instrumentation - Symbolic representation - Part 1: Basic requirements

TC

058

Product Steam

FC

057 Feed M

External

circulation

product

FC FC

Fuel Air

FY

1/λ

RSP

FY

FY >

<

SP

Low

selected

RSP High

selected

Fuel/air control

pH and level control

Coolant inlet

M

TC

TT Reactant A

Reactant B Product

Coolant outlet

Reactor (Exothermic Reaction in CSTR)

CSTR Continuous Stirred-Tank Reactor

Heat exchanger control


RST – Reset Set Point, FC – Flow rate Control, PC – Pressure Control

Condensate

Steam

Feed

FC

Output

RST

TC

Condensate

Steam

Feed

PC

Output

TC

Condensate

Steam

PC

Output

TC

Feed

RSTRST

Cooling water outlet

Cooling water inlet

Feed

Output

TC

Cooling water outlet

Cooling water inlet

Feed

Output

TC

Standard ISO 3511-1 vs. 3511-2


FI 3

Impulse

pipe instruments

3 valves display

ISO 3511-1

Flow rate, Indicating Flow rate, Indication - details

ISO 3511-2

Piping system

Orifice

Flow rate measurement with display at process control console

Servomechanism or position control

Position feedback

Velocity feedback Motor

RP RV Controller output

RP … position controller RV … velocity controller

Ball screw

Ball screw

Linear encoder

Servomechanism for positioning of the table of a machine tool


Reference velocity

Reference position

//upload.wikimedia.org/wikipedia/commons/8/81/BallScrews-with-detail-insets.jpg

A / D Convertors


History

19" × 15" × 26" � 500W � 150 lbs � $8,500.00

1954 "DATRAC" 11-bit, 50-kSPS Vacuum Tube ADC Designed by Bernard M. Gordon at EPSCO

1966 HS-810, 8-bit, 10MSPS ADC Released by Computer Labs, Inc.

1972 ADC-12QZ General Purpose 12-Bit, 40-μs SAR ADC

2" × 0.4" � 1.8 W the first low-cost commercial general-purpose 12-bit ADC on the market

19" rack-mounted �>100W �> $10,000

The acronym SAR actually stands for successive approximation register, and hence the term SAR ADC

http://www.analog.com/library/analogdialogue/archives/39-06/Chapter%204%20Data%20Converter%20Process%20Tech%20F.pdf

Summary of the basic properties of A/D convertors

Type ADC Number of bits Antialiasing filter Delay

Successive approximation

max 12 (14) required Low (depends on the bit number)

Sigma-delta up to 24 not required (a part of the converter)

Large (depends on LP filter order)

Flash 8 (10) required negligible

Bandwidth of the analyzer = number of channels (inputs) x measurement bandwidth

Set of converters with synchronized A / D conversions forms a signal analyzer. The main parameters of the analyzer in terms of number of used converters are simultaneously measured channels and sampling frequency

Frequency range of measurements – theoreticaly:

– in commercial signal analyzer:

2

SR

ff

Sf

56,2

SR

ff


22

Sampling a continuous signal to a discrete signal

Sampling Continuous time t

x(t)

DAC

Discrete time n

ADC

xn

Quantizing noise

0

1

-1 -0,5

p(x) 0,5

x

Quantizing

0

12

15.0

5.0

222

dxxdxxpx

Variance of the quantizing noise

1 2 3 4 5 6

Let x(t) be a continuous signal

Discrete time n

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

p(x) – uniform probability density

12

1

Standard deviation of the quantizing noise

Quantizing is a part of AD conversion resulting in the attribution of values x(nTS) to specified discrete values xn

TS sampling interval


Quantization

• Harmonic distortion – typically characterized by a family of harmonic components resulting from non-linearity in the analog signal conditioning

• Cross-talk – signals caused by inter-channel coupling

• Spurious – signals caused by various phenomena such as power supply imperfection, clock circuits, bus communication and EMC coupling between circuits

• ADC Resolution (given by the number of bits) and non-linearity

• Aliasing originating from signal components of frequencies higher than the Nyquist frequency

Digital output Analog input

Quantizer

A

D Clipping level

Clipping level

Imperfections


Signal analyzers

• CPB (Constant Percentage Band) analyzers, alternatively designated as Real Time or 1/3-octave or 1/1-octave analyzers. The principle is based on a bank of frequency filters with the percentage bandwidth which is equal to a constant.

• FFT analyzers. The principle is based on the Fast Fourier Transform

• Vector analyzers. – It is an analyzer for the measurement of the amplitude and phase of the input signal at a single frequency within an intermediate frequency bandwidth of a heterodyne receiver.

… according to the principle of operation

… according to the application area

• Laboratory analyzers

• Analyzers for machine helth diagnostics

• Analyzers for noise and vibration signals

• Analyzers for electrical signals (frequency range of MHz)

Types of signal analyzers


Brüel & Kjær signal analyzers for laboratory

1996, PULSE™, multichannel analyzer of the BK 3560 type with an external DSP and connection of a front-endu to PC using LAN.

1983 – the first dual channel analyzers of the BK 2032 and 2034 type offers FFT and Hilbert transform

1992, the first multichannel analyzer of the BK 3550 type

End of 90th, PULSE™, multichannel analyzer of the BK 3560 type without an external DSP and connection of a front-end to PC using LAN.

Present days, PULSE™

Before 1980 – High Resolution (narrow band) Signal Analyzer BK 3031 and 2033 (single channel) with a desk-top calculator


SKF Portable signal analyzers for diagnostic practice

SKF Microlog Vibration Spectrum Analyzer and Data Collector

SKF Microlog CMVA 65 Data Collector and FFT analyser

Microlog GX series Microlog MX series Microlog CMXA 51-IS

SKF Microlog Analyzer AX Data Collector and FFT analyser

Condition monitoring


http://upload.wikimedia.org/wikipedia/commons/e/ea/Harmonic_analyser.jpg

Multifunction cards

8 analog inputs (14-bit, 48 kS/s)

2 analog outputs (12-bit, 150 S/s); 12 digital I/O; 32-bits counter

Connection via USB

NI-DAQmx driver software and NI LabVIEW SignalExpress LE interactive data-logging software

Low price multifunction cards NI USB-6009

Products of National Instruments, PCI a PXI.

A card for dynamic measurements, NI USB-4432

5 analog inputs (24bits ΔΣ - convertors, sampling 102.4 kS/s per channel), AC a DC coupling, powering of acc (IEPE)

Input voltage ±40 V,


Sensors properties


Performance terms - 1 Accuracy and error

Error = measured value – true value

Hysteresis error

Input: Physical quantity

Output signal

hysteresis

Non-linearity error


Output signal

Non-linearity error

Assumed relationship

Actual relationship

Insertion error due to the loading

Measurement range

Precision, repeatability and reproducibility

Measured values

True value

High precision, low accuracy

Measured values

True value

Low precision, low accuracy

Measured values

True value

High precision, high accuracy The range of variable of system is the limits between which the input can vary.


Performance terms - 2 Sensitivity


Output signal

sensitivity

1

Dynamic characteristics

Overloading

Sensor dimension

time

Output signal

delay

0 time

Output signal

Time constant

0

Response time

Rise time

Settling time

This is the time taken for the output to settle to within some percentage, e.g. 2%, of the steady-state value.

This is the time taken for the output to rise to some specified percentage of the steady-state output.

This is the time which elapses after the input to a system or element is abruptly increased from zero to a constant value up to the point at which the system or element gives an output corresponding to some specified percentage


Resolution

Principles of sensors


Measuring chain in detail Physical quantity → low voltage → electrical signal (voltage or current) Physical quantity → electrical resistance → electrical signal Physical quantity → force → electric current in the compensation electromagnet → electrical signal Physical quantity → displacement → inductance → electrical signal Velocity → RPM of tachometer → electrical signal Velocity → pulse frequency → electrical signal Velocity → pulse frequency → length of time interval → the electrical signal Velocity → difference frequency → electrical signal The gas content with asymmetrical molecule (CO, CO2) → electrical resistance → electrical signal The oxygen content in the gas → electrical resistance → electrical signal

Basic elements of electrical circuits


Voltage divider (also known as a potential divider)

Vin

Vout

R1

R2 R0

inout V

RR

RRR

RV

02

021

2

Two common schematic symbols for resistor

Electrical load

Inductor

Capacitor

Element Instantaneous Sinusoidal

Resistor

Capacitor

Inductor

iRv

tuCi dd

tiLv dd

IRV

UCjI

ILjV

Potentiometer

US international

Amplifiers and filters


RCjjV

jV

out

in

1

1

Amplifier

Vin Vout

Low pass filter High pass filter

RCj

RCj

jV

jV

out

in

1

Analog passive filters Digital filters

inoutout ykyky 11

Operational amplifier


ΔV V0 = A ΔV

Operational amplifier (“opamp”)

high gain … A (105)

An operational amplifier (op-amp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output.

V1

V0

Voltage follower (Unity Buffer Amplifier)

11

1

10

10

010

AVV

AAVV

VVAV

ΔV V0 = A ΔV

R1

R0

V1

I

1

0

1

0

0

0

1

1

R

R

V

V

R

V

R

VI

Inverting amplifier

10 VV

AFor

- High input impedance - Low output impedance

Impedance transformer

http://en.wikipedia.org/wiki/File:Ua741_opamp.jpg

//upload.wikimedia.org/wikipedia/commons/7/72/Generic_741_pinout_top.png

Integration and derivative of signals

ΔV

V0

R1 R2

V1

Feedback amplifier


ΔV V0 = A ΔV

C1

R0

V1

I

Ideal inverting differentiator

t

VCRV

R

V

t

VCI

d

d

d

d 1100

0

011

V0

C1

R0

V1 Filtr

Inverting differentiator

ΔV V0 = A ΔV

R1

C0

V1

I

Inverting integrator

t

VCR

Vt

VC

R

VI

0

1

01

000

1

1 1 d

d

d

1

1

210

21

110

0

21

110

0

For

1

VR

RRV

A

RR

R

AVV

VRR

RVAV

VAV

Switched-Capacitor Resistor Equivalent


Switched capacitors are replacing resistors. They also allow continuous variation of the resistance by changing the switching frequency. This circuit is composed of a capacitor and analog switches and can be realized in MOS technology (which is based on MOS transistors and capacitors with capacitance in range of farads) with low costs. The switched capacitors is used for tunable filters and tunable and for amplifiers, voltage-to-frequency converters, programmable capacitor arrays, oscillators, amplifiers.

Since the clock signal for the second MOSFET is inverted, one transistor is turned on (its resistance is around 1-10kΩ), and the second is turned off (its resistance is of the order of 1012 kΩ). Therefore MOSFETs can be considered as switches.

C

Clock1 Clock2 = Clock1

Vin Vout

tNVVCtqi 12

Change of the capacitor charge

If the switching occurs N times per a second, then the amount of charge in the capacitor per the time interval of the Δt length, which is an electric current, is

12 VVCq

The resistor equivalent of the circuit can be calculated as

clockCfiVVR 112

where is a clock frequency. tNfclock

Parasitic-Sensitive integrator


The resistance increases with decreasing capacitance or with decreasing switching frequency

Cs

Cfb

Vout Vin

Clock

Resistor

clockfCi

VVR

112

Inverted Clock

tNfclock

Often switched capacitor circuits are used to provide accurate voltage gain and integration by switching a sampled capacitor onto an op-amp with a capacitor Cfb in feedback. One of the earliest of these circuits is the parasitic-Sensitive integrator developed by the Czech engineer Bedrich Hosticka. The time constant of the integrator is adjustable through changes frequency of the clock signal

Req

Switched Capacitor Circuits, Swarthmore College course notes, accessed 2009-05-02.

Parasitic from fringing capacitors and bottom-plate to substrate

C1

Cp1 Cp2

12 %20 CCp

Charge redistribution analysis


http://www.oocities.org/fudinggefilter/Note8_sc1.pdf

• Consider the charge transportation • Op-amp outputs can take/give charge • Op-amp (CMOS) inputs cannot take/give charge • Equilibrium will take place after settling • No charge can disappear from an unconnected capacitor plate • A capacitor with both plates connected to same potential will lose all of its charge

C1

C2 V2 (<0) V1

tVCtq

tVCtq

222

111

C1

C2 V2 V1

2Ttt

22

02

222

1

TtVCTtq

Ttq

tt At At

tqtqTtq 212 2

C1

C2 V2 V1

Ttt

TtVCTtq

TtVCTtq

222

111

At

222 TtqTtq

C1 loses its charge to ground Charge conservation

(>0)

(>0)

(>0) 0 0 0

Transfer Function


http://www.oocities.org/fudinggefilter/Note8_sc1.pdf

Inverting Discrete-time Integrator

tqtqTtqTtq 2122 2

tVCtVCTtVC 221122

zVCzzVC

zVCzVCzzVC

1122

221122

1

1

1

2

1

2

1

1

2

11

1

z

z

C

C

zC

C

zV

zVzH

Z-transform

Transfer function

Wheatstone bridge

R1

R2

Rx

R3 Output voltage

Power supply 32

1

R

R

R

R xR1

R2

R4

R3 Output voltage

Power supply

A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. Its operation is similar to the original potentiometer.

Input: Detector Output: Physical quantity Wheatstone

bridge

Sensor

Voltage signal

strain gauge. resistance thermometer

R is the unknown resistance to be measured

R

The point of balance is the ratio

2

13

R

RRRx

VS

0V

V0

0V

S

x

xG V

RR

R

RR

RV

21

2

3

VG VG

0aI

0bI

0aV

0bV

Output voltage of the Wheastone bridge

VS 4-wire circuit

resistance

Line resistance


Sensors for Displacement


Linear variable differential transformer (LVDT)

Proximity sensor

Strain gauge

Extensometer

Encoder

Magnetostrictive sensor

Displacement sensor

Δx

Δx

Δx

Δx

Δx

Δx

Δx ΔL

Δx ΔL1 ΔL2

Δx

ΔL Δx

ΔV

V0 Δx

V1

V1 V2

V0 V2

A) B) E)

C) D) F)

Capacitive sensing

where C is the capacitance, ε0 is the permittivity of free space constant, K is the dielectric constant of the material in the gap, A is the area of the plates, and d is the distance between the plates.

d

KAC 0

Inductive sensors

The inductance of the loop changes according to the material inside it and since metals are much more effective inductors than other materials the presence of metal increases the current flowing through the loop.

A, C) powered by AC

Δx ΔL

ΔL1 ΔL2

Δx

V = V1 - V2

Δx B, D)

Potentiometer

R1 Output voltage

Power supply R2

VL +VS

0V load

SL Vx

xV

Rx

xR

Rx

xR

12

1


wiper (slider)

(sliding contact)

Linear variable differential transformer


(LVDT)

V2

V1

Δx

Vout = V1 - V2

co

re

Vin LVDT’S AC Output Magnitude

Null Position

50% 100% 0%

AC Output Magnitude of Conventional LVDT Versus Core Displacement

Out Of Phase In Phase

Small-displacement sensors

Z

d

Oscilator Z d

Z0

u0 u

Demod

synchronisation

X

Y

Eddy-current sensor Capacitive sensor

Journal of a sleeve bearing

i ~ d

i2 H2

H1

Softmagnetic ferrite

Steel

Eddy current

magnetic field lines magnetic intensity

Proximity probe


Definition of Strain


Hook’s Law StrainEStress

is the elastic modulus E

Microstrain µε = ΔL / L0 x 106

A microstrain equals the strain that produces a deformation of one part per million.

Strain ε = ΔL / L0

If ε equals to 0.1% then µε equals to 10-3 x 106 = 1000

American English use the word gage. British English is gauge. Except this, both gage and gauge mean the same.

Unstrained rod

Tensil strain Compressive strain

Metallic strain gauges are one of many devices, along with piezo resistors and devices based on interferometric techniques, that have been developed to measure microstrain. Invented by Edward E. Simmons in 1938, the metallic strain gauge consists of a fine wire or metallic foil with an electrical resistance (Ro) adhered to a flat rigid substrate. Ro typically varies from tens to thousands of ohms and the substrate is often referred to as the carrier.

Strain gauge

Metallic strain gauge Metal foil

Term

inal

s

Gauge factor

Semiconductor gauge

GFRR G

21

GRR

GFρ is resistivity

ν is Poisson’s ratio Change in strain gauge resistance

α is temperature coefficient Θ is temperature change

Material Gauge Factor Metal foil strain gauge 2-5

Thin-film metal 2 Single crystal silicon -125 to + 200 Polysilicon ±30 Thick-film resistors 100

46

Leads


120 Ω, 350 Ω, and 1,000 Ω Nominal resistance

Strain gauge type

Backing Encapsulation

Copper-coated tabs

Metallic grid pattern

Sold

er t

abs

Carrier

Strain measurements

Gage pattern

M F T1

T2 T1 T2 T4

T3

F

T2, T3 dummy T1, T4 tension

F Torque Force

overload protection

strain gauge

Force Force

Load cell

Strain

Compression

Force


90-degree rosette

T1

T2

T3

T4

Output voltage

Input voltage

VS

0V VG

Active gauge

Active gauge

Dummy gauge

Dummy gauge

http://www.google.cz/url?sa=i&rct=j&q=half+bridge+strain+gauge&source=images&cd=&cad=rja&docid=OaYNk7eDPWW_0M&tbnid=T8_EzHNVjSh0fM:&ved=0CAUQjRw&url=http://www.alibaba.com/product-gs/484493736/Half_Bridge_Strain_Gauge_BB.html&ei=W609UbvEG9HMswbghIDwDw&bvm=bv.43287494,d.Yms&psig=AFQjCNGJ-QK9inyfTmHbWC9TGBQOv7zC3Q&ust=1363082459278982

http://www.google.cz/url?sa=i&rct=j&q=half+bridge+strain+gauge&source=images&cd=&cad=rja&docid=OaYNk7eDPWW_0M&tbnid=erF_ouySqCJAoM:&ved=0CAUQjRw&url=http://www.alibaba.com/product-gs/484493736/Half_Bridge_Strain_Gauge_BB.html&ei=iq09UYTOO87jtQbOyIDQCQ&bvm=bv.43287494,d.Yms&psig=AFQjCNGJ-QK9inyfTmHbWC9TGBQOv7zC3Q&ust=1363082459278982

Bridge strain gauge circuits Full-bridge strain gauge circuit

Half-bridge strain gauge circuit

Quarter -bridge strain gauge circuit


Signal conditioning for strain gages

• Amplification to increase measurement resolution and improve signal-to-noise ratio • Filtering to remove external, high-frequency noise • Offset nulling to balance the bridge to output 0 V when no strain is applied

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Extensometers


An extensometer is a device that is used to measure changes in the length of an object. It is useful for stress-strain measurements and tensile tests. Its name comes from "extension-meter".

A Zwick Roell Clip-on Extensometer - Measuring Strain on a Metal Specimen.

Properties that are directly measured via a tensile test are ultimate tensile strength, maximum elongation and reduction in area.[

Istron

Encoders Incremental Rotary Encoder

T/4 T

A

B

Absolute Rotary Encoder

T/4 T

A

B

Turn Left Turn Right

Standard binary encoding

Gray encoding

Adjacent codes differ in only one position

Phase between two strings of pulses


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Examples of encoders


Large Bore Hollow Shaft Encoders

Hollow Shaft Encoder Solid Shaft Encoders

Incremental Encoders Absolute Encoders

Parallel Output Format (Single Turn) with Semi Hollow Shaft

High Resolution Encoders They are available encoders with any value resolution from 1 to 65536 pulses per revolution, which in turn can be interpolated by 4 times if required for even greater resolution. A similar miracle can be provided with absolute technology too, up to as much as 20 bit resolution per turn.

Linear Encoders

Magnetic Type Optical Type

http://www.industrialencodersdirect.co.uk/wp-content/uploads/2016/06/110HA-Encoder-1-1.jpg

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http://www.industrialencodersdirect.co.uk/wp-content/uploads/2016/06/58TA-Encoder-1.jpg

http://www.industrialencodersdirect.co.uk/wp-content/uploads/2016/06/MLS-3-Encoder-1.jpg

http://www.industrialencodersdirect.co.uk/wp-content/uploads/2016/06/ALS-Encoder-1.jpg

Uniformity of engine rotation


DC electric motor control

53

time

Voltage Average: high

Average: medium

Average: low

Pulse width modulation (variable duty cycle)

Optical chopper

PID Controller

Pulse width modulator

Feeback

Error DC motor

Frequency to voltage converter

Set point

Tacho

DC motor

Switching transistor or MOSFET

Flywheel (flyback) diode

Logic control


D T

Period Duty cycle … D / T = ξ

0

0

d Uttuu

T

u(t) U0

U0

U0

u(t)

u(t)

A chopper is an electronic switch that is used to interrupt one signal under the control of another (frequency of rotation)

Voltage mean value …

Duty cycle

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Chopper (electronics)


In electronics, a chopper circuit is used to refer to numerous types of electronic switching devices and circuits used in power control and signal applications. A chopper is a switching device that converts fixed DC input to a variable DC output voltage directly. A chopper is an electronic switch that is used to interrupt one signal under the control of another. In signal processing circuits, use of a chopper stabilizes a system against drift of electronic components; the original signal can be recovered after amplification or other processing by a synchronous demodulator that essentially un-does the "chopping" process.

An inverter changes a DC input to an AC output

Rectifiers


AC DC

Diode Transformer

Half wave rectifier

Full-wave rectifier using 4 diodes

Single-phase supply

AC DC

Average

Full-wave rectifier using a center tap transformer and 2 diodes

peakDC UU

peakDC UU 2

peakDC UU 2

//upload.wikimedia.org/wikipedia/commons/5/58/Halfwave.rectifier.en.svg

//upload.wikimedia.org/wikipedia/commons/d/d5/Gratz.rectifier.en.svg

http://en.wikipedia.org/wiki/File:Fullwave.rectifier.en.svg

Magnetostrictive sensors


http://www.mdpi.com/1424-8220/11/5/5508/htm

Linear position sensors based on magnetostrictive effect are widely used for position measurement. In accordance with the Wiedemann effect and the Villari effect, the magnetostrictive linear position sensor (MLPS) uses a ferromagnetic material waveguide to perform accurate position measurements.

Pressure transducer

Wire

Measuring diaphragm

Isolating diaphragm

Glass Silicone oil Silicon

Strain gauge arrangement on a diaphragm

Strain gauges

Pressure

strain compression

The movement of the centre of a diaphragm can be monitored by some form of displacement sensor.

Diaphragm sensor


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Force-to-current converter

R F

I

UR

F*

Force = surface area x pressure

ΔU

Δx Δx

Displacement sensor

pressure

coil A lever in balance

Pressure -

Pressure +

Current

Bellows


magnet

Impulse pipe

Liquid level sensors

Displacement

Float

Pressure Min Max Capacitive sensor Transmitter receiver

conductivity ultrasound hydrostatic pressure

ghp


Radionic gauges

Sou

rce

Det

ecto

r

Conductivity methods can be used to indicate when the level of a high liquid reaches a critical level.

The source of gamma radiation is generally cobalt-60, caesium-137 or radium~226. A detector is placed on one side of the container and the source on the other.

Load cell

Bin

Bulk material

Volumetric flow rate measurement

Sharp-edged orifice

p1 p2 p1 p2

Long radius nozzle

p1 p2

Venturi tube

313

1 kgmPa,;sm,

pkQ KPa,Pa,;sm, 013

2

T

p

pkQ

pressure drop, p density

liquid

Δp

Pressure drop sensor

steam orifice

condensate pot

gas

5 valves

Impulse pipe

Orifice plate Carrier ring

Annular slot Equalising valve

Test point

Primary isolating valve

Secondary isolating valve

An orifice plate is a device that measures the flow rate of fluid in a pipe.

Orifice plate

60

Measuring orifice


Orifice plate installation

Flange

pipe elbow pipe diameter

Orifice plate installation - how much straight pipe should be upstream and downstream?

Flange

DL 101

pipe elbow

DL 51

Orifice

D

upstream downstream


//upload.wikimedia.org/wikipedia/commons/b/b8/Blende_eng.png

//upload.wikimedia.org/wikipedia/commons/0/0f/Orifice.png

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Pressure difference measurements

62

Simple pitot tube

Pitot-static tube


Static pressure

Total pressure

Static pressure

Total pressure

Strain gages

Bellows Bellows

Pressure measurement with strain gauge on bellows

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Flow rate measurement

v

E

N

S B

v Impulse sensor

v

Flow rate is proportional to rotational frequency

Karman effect Magnetic flow meters Turbine flowmeter

Vortex

For a particular bluff body, the number of vortices produced per second, is proportional to the flow rate. For example, a thermistor, heated as a result of a current passing through it, senses vortices due to the cooling effect caused by their breaking away.

bluff body

B magnetic field v velocity L length of conductor E voltage

E = B v L

for conductive process medium Sensing

electrodes


Temperature sensors


Bimetallic strip

The metals have different coefficients of expansion

Liquid in glass thermometers

Resistance temperature detectors

Thermistors

Thermocouples

Thermodiodes and transistors

Pyrometers

The liquid in glass thermometer involves a liquid expanding up a capillary tube. The height to which the liquid expands is a measure of the temperature. (mercury alcohol, pentane)

Platinum, nickel or copper alloys

tRR 10

Thermistors are semiconductor temperature sensors made from mixtures of metal oxides, such as those of chromium, cobalt, iron, manganese and nickel.

When the temperature of doped semiconductors changes, the mobility of their charge carriers change. As a consequence, when a p-n junction has a potential difference across it, the current through the junction is a function of the temperature.

Resistance thermometer

Pt 100 T

Vzdálená

instalace

Pt 100 T

I = konst

Pt 100 T

Four-wire configuration Three-wire configuration Two-wire configuration

Pt – 100, resistance for temperature of 0°C 100 Ω


(alternatively Pt – 500, Pt – 1000)

//upload.wikimedia.org/wikipedia/commons/e/eb/Rtdconstruction.gif

//upload.wikimedia.org/wikipedia/commons/8/80/Coil_Element_PRT.png

Temperature-dependent resistances


Temperature Resistance in Ω

in °C ITS-90 Pt100

Pt100 Pt1000

Typ: 404 Typ: 501

−50 79.901192 80.31 803.1

−40 83.945642 84.27 842.7

−30 87.976963 88.22 882.2

−20 91.995602 92.16 921.6

−10 96.001893 96.09 960.9

0 99.996012 100.00 1000.0

10 103.977803 103.90 1039.0

20 107.947437 107.79 1077.9

30 111.904954 111.67 1116.7

40 115.850387 115.54 1155.4

50 119.783766 119.40 1194.0

60 123.705116 123.24 1232.4

70 127.614463 127.07 1270.7

80 131.511828 130.89 1308.9

90 135.397232 134.70 1347.0

100 139.270697 138.50 1385.0

150 158.459633 157.31 1573.1

200 177.353177 175.84 1758.4

Thermocouple

thermostat 500C

Copper cable

terminals

Hot junction T1 T2

A B voltmeter

Cold junction Properties of thermocouple circuits

Long length of extension cable

Head

Measuring junction Conductors Sheath Insulator

Metal A

Metal B


Material EMF versus temperature

With reference to the characteristics of pure Platinum

emf-electromotive force

68

alloy


Themocouple characteristics table

Class 1 Class 2 Class 3

Thermocouple Range [° C] Tolerance

[° C] Range [°C]

Tolerance [° C]

Range [°C] Tolerance [°C]

T Cu-CuNi -40 to 350 ±0,5 or

±0,004 T -40 to 350

±1,0 or ±0,0075 T

-200 to 40 ±1,0 or ±0,0015 T

E NiCr-CuNi -40 to 800 ±1,5 or

±0,004 T -40 to 900

±2,5 or ±0,0075 T

J Fe-CuNi -40 to 750 ±1,5 or

±0,004 T -40 to 750

±2,5 or ±0,0075 T

K NiCr-Ni -40 to 1000 ±1,5 or

±0,004 T -40 to 1200

±2,5 or ±0,0075 T

-200 to 40 ±2,5 or ±0,0015 T

N NiCrSil-NiSil -40 to 1000 ±1,5 or

±0,004 T -40 to 1200

±2,5 or ±0,0075 T

-200 to 40 ±2,5 or ±0,0015 T

S Pt10Rh-Pt 0 to 1100 (… to 1600)

±1,5 or ±0,004 T

0 to 1600 ±1,5 or ±0,0025 T

R Pt13Rh-Pt 0 to 1100

(… to 1600) ±1 or ±0,004

T 0 to 1100

±1,5 or ±0,0025 T

B Pt30Rh-Pt6Rh 600 to 1700 ±1,5 or ±0,0025 T

600 to 1700 ±4 or ±0,005 T


Installation of thermocouples

Termination head

Nipple

Union

Nipple


Pyrometers


Total radiation pyrometer Disappearing filament pyrometer

Vibration measurement


Vibration – fundamental formulas

Displacement [m], [mm] ……………..

Velocity [m/s], [mm/s] ………………..

Acceleration [m/s2], [g] ……………..

tAtXtx

tAtXtx

tAtXtx

coscos

sinsin

coscos

2

2

aREF = 10-6 m/s2 ][log20 dB

y

yL

REF

RMS

Reference (RMS)

Relative units, level in dB

vREF = 10-9 m/s = 10-6 mm/s

(FREF = 10-6 N force) 1 g ... 20 log(10/10-6) = 140 dB

3-2

Sinusoidal functions of time

dttyT

y

T

RMS 0

21

Root Mean Square (RMS) of a signal y(t)

Root Mean Square

t t

tttatx0 10 22 dd1

t

ttatx0 11 d

tatx


Effect of frequency on amplitude of acceleration and displacement

Frekvence

0

20

40

0 10 20 30 40 50

Time [s]

Výchylka

-2-1012

0 10 20 30 40 50

Time [s]

Rychlost

-2-1012

0 10 20 30 40 50

Time [s]

Výchylka

-2-1012

0 10 20 30 40 50

Time [s]

Rychlost

-50

0

50

0 10 20 30 40 50

Time [s]

Zrychlení

-1000

0

1000

0 10 20 30 40 50

Time [s]

Zrychlení

-2-1012

0 10 20 30 40 50

Time [s]

Frekvence

0

20

40

0 10 20 30 40 50

Time [s]

1 Hz 1 Hz

30 Hz 30 Hz

3-3

Vibration with a constant amplitude of acceleration Vibration with a constant amplitude of displacement

Displacement

Frequency

Acceleration

Velocity Velocity

Acceleration Displacement

Frequency


Dependency of amplitude on frequency

flog

Ampl log

acc

disp

vel A constant

flog

Ampl log

acc

disp

vel

A constant

Logarithmic coordinates

Amplitude Amplitude

frequency Frequency

2 dec/1 dec

1 dec/1 dec

0 dec/1 dec

Constant amplitude of acceleration Constant amplitude of displacement

3-4

Nomogram: an aid for the conversion of the oscillation amplitudes of acceleration, velocity or displacement for a selected frequency


Sensors, transducers

Displacement – proximity probes

Velocity – velocity transducers

Acceleration – accelerometers

Accelerometers

Piezoaccelerometers (generate electric charge)

Piezorezistive (changes the electrical resistance)

Accelerometers with variable capacitance (iMEMs)

3-5

The vibration sensor can be divided according to their primary output, i.e. a signal which does not need to integrate or calculate derivative to obtain a different signal than originally measured (e.g., the measured acceleration is not integrated in addition to obtain velocity).


Operational range of transducers

Frequency

Relative amplitude

Piezoelectric accelerometers

Transducer of velocity

Eddy current, Proximity probe

3-6

0 Hz


Proximity probe Proximity probe

Oil wedge

Proximity probes

Orbit plot

Journal bearing

Measured displacements d of the order of microns to millimeters with a frequency range of 0-10 kHz. The sensitivity of the sensor depends on material of the surface

-150

-100

-50

0

50

100

150

-150 -100 -50 0 50 100 150

mikron

mik

ron

Axis X

Axis Y Benefits from eddy current i2

3-7

i ~ d

i2 H2

H1 Magnetic field H1 is weakened by a field polem H2

The conductive material (usually a shaft, which may not be hollow)

Amplitude of alternate current i is modulated by varying d


Transducers of velocity

Seismic mass m (movable coil)

Vibrating pad

y

x v

yxBlBlvE REL

yxbyxkym

The induced voltage is proportional to the relative velocity of the coil with respect to the pad

Movable coil

Permanent magnet

Equation of motion

RELREL bvsvkysm 2

RELREL vbtdvkym

xksbysbsm 12

ksbsm

sm

v

vREL

2

2

Measurement ranga

flog

vvRELdB f0

System is weakly damped

kmkb 212

1

km

b

Restricting the frequency range:

10 Hz < f < 1000 Hz

Hinge

3-8

1222

22

sTsT

sT

v

vREL

0

kmT

yxvREL

Relative velocity of permanent magnet with respect to the coil


Sensors using the inertial mass

m

Electric signal

Seismic mass m

The piezoelectric material like spring

Measurement range

y

x

ysmsvmamF 2 ysxsbyxkF

ymvmamF yxbyxkF

12

122

1

sTsT

sTm

a

F

2

111

sm

k

sm

b

sbk

x

F

flog

aFdB

+10%

Vibrating pad

0,3 f0

f0

a

+35 dB

Piezoelectric materials generate an electrical charge proportional to the force acting on it.

The system is slightly dampened

kmkb 2

kmT

m

k

m

bss

sbk

xs

F

a

F

22

1

Tf

1

2

10

k

bT 1

1

11

2

1

TT

3-9

Transfer function relating the force applied to the piezoelectric material to acceleration

Equation of motion

km

b

2

1

The acceleration sensor operates in the frequency band below the resonance, while the speed sensor operates in the range above the resonance


Operating principle of piezoelectric accelerometers

Pressure Shear

FQ

induced charge Q is proportional to force F

FQ

NpC NpC

3-10 (C) Jiří Tůma, 2016

Piezoaccelerometers

BK charge amplifier Accelerometers with an integrated charge amplifier

Electrical supply CCLD - Constant Current Line Drive

2 to 20 mA

Current source

Accelerometer

Alterning voltage

Coaxial cable with a parasitic capacitance in pF per meter

Output

Charge amplifier

alternating voltage

Output A/D:

Accelerometer without charge amplifier

These accelerometers do not measure static acceleration due to low frequency temperature drift

Accelerometer with a high internal resistance

3-11

(18 až 30 V)

IEPE - Integrated Electronics Piezo Electric

or ICP®, Isotron®, Deltatron®, Piezotron®

Acc model


Design of accelerometers

3-12

P: piezoelectric element S: spring E: embedded electronics B: base R: fixing ring (C) Jiří Tůma, 2016

Big or small accelerometer?

3-13 (C) Jiří Tůma, 2016

Mass Mass Acceleration

Frequency

Sensitivity

Special accelerometers Shock accelerometer

Triaxial accelerometer

Range: 20000 to 80000 g

3-14

(The charge amplifier is not embedded in accelerometer, but outside like connector.)

Kalibrační akcelerometr

Accelerometer to be calibrated

Shaker

Calibrator

Acc = 10 m/s2

= 1000 rad/s

Freq = 159,2 Hz

Calibration of accelerometers

Accelerometer to be calibrated

Calibrated accelerometer vibrates like a reference accelerometer.


Calibration accelerometer

Piezorezistive accelerometers

3-15

inertial mass

Embedded electronic

Piezorezistive material

Strain gauge

Accelerometer as part of the IC

Movable cantilever beam

These accelerometers can be designed for measurements from 0 Hz, ie. for static acceleration measurement (eg. gravity acceleration)


Piezorezistive Accelerometers DC Response Accelerometers

Wheatstone bridge

Cable

Type 4570

The accelerometer measures static acceleration (hence DC)

3-16 (C) Jiří Tůma, 2016

Principle of MEMS accelerometers

iMEMS: Integrated Micro–Electro Mechanical System

Direction of measurement

Substrate

anchoring Capacitor electrodes for measuring displacement

Analog Devices ADXL105

A uniaxial accelerometer, a range of ± 5 g Analog Output Sensitivity 2mg Frequency Response of 10kHz

Simultaneous measurement of temperature Low-power charge 2 mA at 5V,? The loss of functional abilities at 2.7V Additional Amplifier Surface Mount

(Variable Capacitance)

3-17

Suspension for movement in the direction of arrow


MEMs accelerometers

3-18

Direction of acceleration

Resistance bridge for strain gauges


Selecting the measuring place

We avoid places that could easily resonate like covers, lids, etc.!

It is not advisable to place the accelerometer eg. in the middle of a planar housing, etc.

3-19 (C) Jiří Tůma, 2016

Mounting accelerometers to measuring point

3-20

Permanent magnet

Hand held

Threaded stud

cement Thin double-sided adhesive tape

beeswax


Level

Frequency

Noise measurement Measurement Microphones

Sound pressure, sound pressure level

pREF = 20 μPa

dBlog20

REF

RMS

p

pL

RMS

Reference (RMS)

Relative units

Barometric, sound pressure, total pressure

0p tp tpptpCelk 0

103 kPa Less than unit of Pa

Absolute units tp

dttpT

p

T

RMS

0

21RMS

(threshold of hiring at 1 kHz)

Sound pressure level ... SPL (dB)

čas

pRMS = 20 μPa ... 0 dB

pRMS = 1 Pa ..... 94 dB

5-2 (C) Jiří Tůma, 2016

Tima

Transducers of sound pressure - measuring microphones

Sound field

Condenser microphone

Balancing the static pressure before and behind of the membrane

Outside of sound field Inside of sound field

Size from 1/8’’ to 1’’

5-3

Vent Vent

Sound field


Microphone with preamplifier

Sensitivity: 50mV / Pa Frequency: 6.3Hz to 20kHz Dynamic range: 6.14 to 146 db Temperature: .30 to + 150 ° C Polarization: 200V (20 V)

Microphone

Amplifier Coupling capacitor

Source for polarization voltage U

Electric resistance

Full electromagnetic compatibility (EMC) Detachable, thin cable for easy installation Compact LEMO connector and preamplifier Charge-injection calibration (CIC) technique Very low noise, high input impedance Low output impedance

½″ Free-field Microphone Type 4190

Preamplifier Type 2669C

td

CUd

td

Qdi

iPolarization voltage is 200V, 20V or 0V

5-4

If U = konst, then

td

dCUi

Changes in sound pressure excites changes in the capacitance

Membrane Backplate


Microphone windscreen protection

5-7

Microphone without windscreenu

Microphone windscreen

Windscreen of foam prevents air flow turbulence at the edges of the lattice and thus the parasitic noise

Protection against wind, rain and birds, who could sit down for microphone

Microphone for outdoor measurements


Electret microphone with polarization

Electric field

Membrane

5-8

Microphone Type: 1/2”, omni-directional (všesměrový), pre-polarized condenser, free field transducer

Sensitivity : balanced (20 ±2) mV/Pa, unbalanced (10 ±1) mV/Pa @ 1 kHz, 20°C +0.05 dBSPL / °C

Frequency Response: Class 2 acc. to IEC60651, tolerance curve is shown on individual calibration certificate

Peak Acoustic Input : 130 dBSPL @ 1 kHz

Noise : 32 dBSPL, A-weighted

Load Conditions : 20 - 200 kOhm balanced

Power Supply : 1x AA battery 1.5 V, battery lifetime typical 300 hrs, no phantom power supply, phantom power resistant

Dimensions: 22 x 180 mm, 0.87” x 7”

Weight: 100 g ( 3.5 oz ) incl. battery

Backplate

Air gap

Membrane

Electret microphones does not require polarization voltage

NTI Mini SPL Measurement Microphone (low price)


Surface microphones and MEMS microphones Surface microphone manufacturer by Brüel and Kjær. Types 4949 and 4949B are designed for small and medium noises on the surface of objects.

Properties - Sensitivity: 11.2 mV / Pa - The frequency range of 5 to 20 kHz - Dynamic range: 30-140 db - Temperature: 30-100 ° C - Built-Delta-Tron amplifier - There is a mounting pad TEDS. IEEE P1451.4 Connecting to CCLD / DeltaTron® input - CIC verification of input sensitivity embedded hub (Type B 4949)

5-9

MEMS Microphones, manufacturer Analog Devices, type ADMP401 ADMP421 are worth about $ 1 is $ 2.

Type ADMP401 has an analog output, while ADMP421 contains ΔΣ - 4th order modulator and therefore has a digital output.

3.7

6 m

m

4.72 mm

1 mm

hole

1

1, 2, 4, 5, 6

3

4 5

2

6

terminals

Both microphones have a flat frequency characteristic in the band from 100 Hz to 15 kHz. Signal to noise ratio S / NDB is 60 db? Suppression and changes in the supply voltage PSRR? Is 70-80 db.


Microphone array

5-10

The array is used to obtain input data for the spatial transformation of sound fields (STSF - Spatial Transformation of Sound Fields) and holography close acoustic field (Near-field Acoustic Holography). The first method predicts the acoustic field at any distance from the source and the second method allows you to identify the source of the noise.

Typ 4961

¼’’ Multi-field Mic


Measurement Sensors Devices -...

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