Proveden

1
Experimental methods E181101
EXM4
Displacement, Deformation,Pressures
Some pictures and texts were copied from
www.wikipedia.com
Rudolf Žitný, Ústav procesní a zpracovatelské
techniky CVUT FS 2010
2
DISTANCEs or how to measure geometry of samples
(thickness)
EXM4

• Unit of length 1 m (defined in terms of speed of
  light)
• In laboratories/industry are used the following
  MECHANICAL instruments
• Calipers
• Gauge blocks (Johansson gauges)
• Micrometers

Rudolf Žitný, Ústav procesní a zpracovatelské
techniky CVUT FS 2010
3
DISTANCEs or how to measure a motion of samples
electronically
EXM4

• In laboratories/industry are used the following
  ELECTRICAL sensors
• Inductive (eddy current sensors, impedance of
  coil depends upon distance from metallic sheet)
• LVDT Linear Variable Differential Transformer.
  Three solenoidal coils are placed end-to-end
  around a tube. The center coil is the primary,
  and the two outer coils are the secondaries. A
  cylindrical ferromagnetic core slides along the
  axis of coils. An alternating current (frequency
  1 to 10 kHz) is driven through the primary coil,
  causing a voltage to be induced in each secondary
  proportional to its mutual inductance with the
  primary.

Maximum sensing range is roughly coil radius.
Linearity 1, resolution in ?m. Driving
frequencies up to 50 kHz.
Lag and amplitude 1 ?m
Mention the fact, that the two transducer
secondaries are connected in opposition.
Therefore at central position of feromagnetic
core the resulting voltage is zero.
Rudolf Žitný, Ústav procesní a zpracovatelské
techniky CVUT FS 2010
4
DISTANCEs
EXM4

• In our laboratories the following ELECTRICAL
  sensors are used
• Potentiometers (linear, string-the spool is
  coupled to the shaft of a rotational sensor, you
  will see this arrangement in our laboratory
  piston displacement of extrusional rheometer
  measurement).
• The same principle is used in the project
  SYRINGE, see Fig.

Specific electrical conductivity of liquid in
syringe S/m
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DISTANCEs
EXM4

• The following OPTICAL instruments will be used in
  your project (inflation test)
• Laser scanner ?Epsilon
• Confocal probe Chrocodile M4
• Cross-correlator Dantec Q 450

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Laser scanner
EXM4
Wikipedia (Laser scanner) A laser rangefinder is
a device which uses a laser beam to determine the
distance to an object. The most common form of
laser rangefinder operates on the time of flight
principle by sending a laser pulse in a narrow
beam towards the object and measuring the time
taken by the pulse to be reflected off the target
and returned to the sender. Due to the high speed
of light, this technique is not appropriate for
high precision sub-millimeter measurements, where
triangulation and other techniques are often used.
3D laser scanner shines a laser on the subject
and exploits a camera to look for the location of
the laser dot. Depending on how far away the
laser strikes a surface, the laser dot appears at
different places in the cameras field of view.
This technique is called triangulation because
the laser dot, the camera and the laser emitter
form a triangle. The length of one side of the
triangle, the distance between the camera and the
laser emitter is known. The angle of the laser
emitter corner is also known. The angle of the
camera corner can be determined by looking at the
location of the laser dot in the cameras field
of view. These three pieces of information fully
determine the shape and size of the triangle and
gives the location of the laser dot corner of the
triangle. In most cases a laser stripe, instead
of a single laser dot, is swept across the object
to speed up the acquisition process.
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Confocal probe
EXM4
The chromatic coded principle utilises the
chromatic length aberation of specialised lens to
measure distance and transparent layer thickness.
Due to the independence of surface properties
merely all materials can be measured by the
sensor. The measurement range of the sensor
stretches from some micrometers up to millimeters
with corresponding resolution. The passive sensor
probe is connected via an optical fiber to ensure
the operation in problematic or hazardous
environment like strong electromagnetic fields,
vacuum or explosive areas.
Light is reflected from the point of changing
refractive index
8
Cross-correlator
EXM4
The Digital 3D Correlation System Q-450 is used
for non contact measurement of surface and
deformation of any object. A stochastic pattern
is applied onto the surface of the test object.
This pattern can be sprayed with a white base
colour and spattering a black colour on top. The
surface is observed with two high-speed CCD
camertas. In each captured image homologous
points of the stochastic structure are identified
using a specific pattern matching algorithm. The
three-dimensional position of each object point
is determined by triangulation performed by the
software. How?
This is in principle matter of a pure geometry
knowing x1,y1 and x2,y2 position (pixels) of the
same material point in the two 2D images recorded
by two cameras, it is possible to evaluate its
coordinate x,y,z in the 3D space. It can be
illustrated schematically in a 2D reconstruction
of point (x,y) from the two 1D images x1, x2
In 3D there are two cameras giving 4 coordinates
(x1,y1, x2,y2) of point x,y,z. This is
overdetermined problem!
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Cross-correlator
EXM4
10
Cross-correlator DIC
EXM4
Digital image correlation algorithm is based upon
assumed mapping between two images from camera.
The goal is to identify a shift (displacement)
and deformation of material points. The whole
image is divided to sub-images, called facets (a
set of material points). It is assumed that the
material facet in the second image is shifted (by
displacements u,v in the x,y directions) and
linearly deformed (gradient of displacement)
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Cross-correlator DIC
EXM4
6 parameters u,v (shift) and gradient (du/dx,)
should be identified at each facet. These
parameter (spatial transformation) are selected
in such a way that the correlation between
corresponding material points in both images
(initial and deformed configuration) is
maximized. It is assumed that each material point
has the same intensity of pixel in both images
(intensity F in the first and G in the second
image). Then the correlation rij between pixels
i,j in both images (facets) can be expressed as
Maximum rij corresponds to optimal values of
displacement and deformation in a facet.
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Grid-Facet DIC
EXM4
Problem !) averaging DIC params 2) Interpolation
DIC We do not know how it is implemented in Q 450
Grid
Facet
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Grid-Facet DIC
EXM4
Grid
Facet
14
OCT , ESPI
EXM4
There are many other different optical methods
based upon interferometry, see e.g. OCT (Optical
Coherence Tomography)
ESPI means Electronic Speckle Pattern
Interferometry and it is similar to previously
described DIC
15
Pressure
EXM4
16
Pressure
EXM4
Units and terminology Gauge pressure relative
to atmospheric (Pa gauge, psig) Absolute pressure
(psia)

• Instruments for pressure measurement
• U-tube

Micromanometers Askania extremely accurate
(used as a gauge)
Resolution 0.1 Pa !!
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Pressure
EXM4

• Instruments for pressure measurement (mechanical)
• FLEXIBLE elements
• Bourdon tube C/shape-oval
• Bellows elements
• Diaphragm

Can you explain how the Bourdon tube will be
deformed by internal pressure? And why?

18
Pressure
EXM4

• Instruments for pressure measurement (electronic)
• Piezoresistive Strain Gage (piezoresistive effect
  of bonded or formed strain gauges to detect
  strain due to applied pressure)
• Capacitive (a diaphragm create a variable
  capacitor)
• Magnetic (diaphragm displacement measured by
  inductance, LVDT, Hall Effect, or by eddy
  current).
• Piezotransducers (piezoelectric effect in certain
  materials such as quartz to measure the strain
  upon the sensing mechanism due to pressure).
• Optical (physical change of an optical fiber
  with strain)
• Resonant (changes in resonant frequency of a
  string, crystal, gas)

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Do you understand principle?
EXM4
Ultra-precision micro-differential pressure
measuring device and ultra-precision differential
pressure measuring device Patent Sekoguchi,
Kotohiko (8-10-1304 Sakaemachi, Ikeda-shi, Osaka,
JP)
20
Strain gauge
EXM4
SG - Resistor with electrical resistivity
dependent on strain Gauge Factor
deformation
There are two basic types of SG Foil SG. Metallic
wire (e.g. constantan) included in a thin plastic
sheet. The foil is bonded to surface of measured
object e.g. by cyanoacrylate glue. Typical gauge
factor is 2 and resistance 120? (almost the same
as resistance of Pt100 thermometers. Therefore
the same technique for measurement of electric
resistance Is used (Wheatstone bridge). Problem
with temperature dependent resistance can be
compensated using 2 SG bonded to the surface at a
place with the same temperature (half bridge), or
even 4 active SG at the same temperature (full
bridge). Selfcompensated SG make use of metallic
wire adjusted to the thermal expansion of basic
material. Semiconductor SG (piezoresistive).
Silicon wafer or rod doped by Germanium or As.
Much higher sensitivity (gauge factor),
but also sensitive to temperature.

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Piezoresistive transducers
EXM4
Exposed silicon membrane
Separating membrane silicon oil
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Piezoresistive transducers
EXM4
KULITE XTM 190 this transducer is used in the
project SYRINGE.
Please, be careful as concerns the wiring and
polarity of voltage