8/12/2019 2.a.omniscan Setup - Calibration for Sectorial Scan
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By Nick Bublitz
Performing a Sectorial ScanSensitivity/ Velocity/Wedge Delay
Calibration-Shear Wave PA Using
SDHs at Known Depths 2.0 SW
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Calibrations-Required items
Calibration block with 2 same size reflectorsat known depths- (Navships block with
SDHs or other calibration block with 2 same
size reflectors at known depths)Couplant-water works best for practice-
otherwise whatever you will test with
Guide to keep from skewing- use a ruler, setthe block on its side, or on IHC wedges can
screw down one sides carbide pins.
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Velocity Calibration
The velocity calibration will fine tune the velocity to that ofthe calibration block. It will require two reflectors of thesame size at two different known depths (Depth). A radiusmay also be used in sound path overlay (Radius) .
In many cases the default material velocity and wave type
set by the operator in the group wizard is sufficient and thiscalibration can be skipped because wedge delay will adjustaccordingly to allow accurate measurements in the depthaxis.
If performed the velocity calibration should be done beforethe wedge delay calibration. Performing a velocitycalibration after wedge delay will remove the wedge delaycalibration.
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Velocity Calibration
Just like Con. UT the velocity calibration will calculate the time
difference to two reflectors of known depth or sound path and
calculate a material velocity. Many conventional users use an IIW
block (radius), in PA we often use true depth rulers so a Navshipsworks well (depth)
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Select Velocity Calibration
Go to the Wizard-Calibration menu
Select Ultrasound and
Velocity
Start the wizard
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Select A-Scan
Put the probe on yourblock over the first
reflector.
Choose an angle near the
middle of your anglesweep using the angle
function. The calibration
will utilize a single beam
as the velocity will be
consistent across all the
angles.
Adjust range as needed to
ensure you will see the 2
reflectors you have chosen.
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Set Gate A on Depth 1
Move probe back and forthover the first reflector
building an envelope. Use
a guide so you do not
skew right or left. Ensure you peak the
reflector.
Adjust the gate to
encompass the reflector. Get position.
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Set Gate A on Depth 2
Repeat the peakingprocess on your
second reflector.
Adjust the gate to
encompass this
reflector.
Get position.
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Accept or Restart
View the velocitydetermination
If it is sensible accept the
calibration, if not restart.
Depth readings may not be100% accurate after a
velocity calibration at all
angles due to the different
wedge path distance ofindividual beams. Wedge
delay calibration will
compensate for this.
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Set Section
Decide if you want tocalibrate the whole
angular sweep or
break it up into
separate calibrations-for most setups with a
good calibration block
you can calibrate the
whole sweep. Hit Next
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Set Gate A on Depth A
Put the probe on the block soyou can see the chosen
depth reflector.
Adjust the gate
start/width/threshold toencompass the reflector.
Move the probe forward
and backwards to ensure
gate is encompassing
reflector through all angles
and there are no other
reflectors that will affect
calibration.
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Calibrate and Accept
Move the probe forwardand backward applyingeven pressure andavoiding skewing right orleft.
Move in both directionsuntil the green line is builtacross the whole angularrange. Adjust gain asneeded.
Hit calibrate.
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Accept or Restart
After hitting calibrate-rerun the probe
through the angular
range verifying you are
within the settolerance.
Accept or Restart.
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Verifying Wedge Delay
Set the DA reading fromthe Measurement-Readings menu
Turn on the Highest %feature in the Display-
Properties-Source menu Run the probe through the
angular sweep whileobserving the DA reading.
The Omniscan will trackthe highest reflector in thered gate. Return thesource to normal beforenext calibration!
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Sensitivity Calibrations
Sensitivity calibrations equalize the sensitivity(amplitude) to a given reflector through all the
angles.
This will insure no matter what angle the reflector
is seen at the % FSH is the same for rejection or
detection purposes as well as for the amplitude
based color coded imaging selections. Calibration
reflector and natural flaw response relies heavilyon angle so it is critical each beam/angle can be
calibrated to the same sensitivity level.
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Sensitivity Calibration
Enter Calibration menuand select Sensitivity
Choose a reference
screen height to equalizesensitivity to (80% FSH)and a tolerance. Thedefault tolerance of 5% willshow two linesone 2.5%
above your set reference,one 2.5% below. This doesnot affect the quality of thecalibration it is merelyvisual reference.
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Getting Started
Choose a SDH andcouple your probe
above it
Use a guide system to
keep the probe from
skewing side to side.
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Set Section
Choose whether tocalibrate the whole
angular sweep in one
step or break it up into
separate calibrations-if your calibration block
has adequate spacing
between SDHs you
can usually do the
whole range.
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Set Gate A on Echo A
Set the gate to encompass theSDH reflection. Adjust the
start/width/threshold of the gate.
Move the probe forward and
backward to ensure the gate
covers the reflector through all
the angles and there is not on
any other reflectors that may
inhibit the calibration
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Set Compensation Gain
Allows you to adjustthe gain as needed toensure the reflector isseen properly
throughout all theangles
In most cases noadjustment or an
adjustment of theoverall gain (if overreference level FSH%)is needed.
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Calibrate and Accept
Press Calibrate Verify the calibration
by repeating theforward and backward
movement of the probe The green line should
fall within the definedtolerance lines across
all the angles.Accept or Recalibrate
as needed.
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To Verify Sensitivity Calibration
To verify sensitivity go toDisplay menu
Select properties
Change source to Highest
Run the probe back and forthand observe FSH in the
A% reading field as the
data cursor tracks the
highest amplitude signal inthe red gate. Return the
source to normal before
further calibrations!
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General Tips for Calibrations-Omniscan-General
Even pressure and couplant are key- practice
makes perfect. Practice with water-it doesntshovel like gel couplant.
A good calibration block helps a lot- theNavships block is a great block for PAcalibrations. Tighter spacing of reflectors mayrequire breaking up the calibrations into two ormore sections using the set section feature tokeep other reflectors from entering the gatedtracking area.
A guide will ensure sure the same portion ofthe beam sees the reflectorthis is key
The Omniscan must see the natural state(building of green line) between about 10%FSH and the high tolerance set.
Instead of restarting calibrations you canreduce gain, rebuild green line and hit
calibrate again. If the green line drops off suddenly examineyour a-scan at the point it drops, your gatethreshold and/or width may need adjustment.
Utilize the scan view for setting gates, lookingfor interfering reflectors- it is a tendency forcon. ut operators to look at only the a-scan-remember this is only one angle in a sweep.
max tolerance line
10% FSH
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General Tips for Calibrations-Omniscan settings
Ensure the tracking function is set tonormal-Display-Properties-Source-Normal, since the wizards use a trackingsystem Highest/Thinnest/All Laws caninterfere
Make sure you are set to run off theclock of the Omniscan, not an encoderbase-Scan-Inspection-Scan-Time-lookin right hand corner-should be inseconds.
Make sure db reference is off- Utsettings-Advanced-db Ref-Off look in lefthand corner
These are all set ok by default but if youcreate a setup and have issues these
are key places to look. Sluggish-low PRF- ensure gates are all
on screen and minimized, minimizerange etc
All of the above usually result in nogreen line at all of a very sluggish jerkytracking response.
No db ref ( )
x: sec
prf
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General Tips for Calibrations-Omniscan
Rounded irregular hills in green line-
usually due to uneven pressure orskewing left/right, also excess couplantin that area- hold probe with evenpressure, use a guide and apply evencouplant between wedge and block.
Green line not able to be set between
reference and 10% for training- adjustgain, use comp. gain, reduce angularsweep or change wedge. Comp. Gainwill add an amount of gain per us oftravel- longer beam paths (higherangles) will thus have more gain addedto facilitate proper calibration. Lowerwedge angles will be easier bent to lowangles, the opposite for highera 45degree wedge is easier to calibrate at 30degrees, a 60 degree wedge will beeasier calibrated at 72 degrees. 55degree wedge is a good wedge for bothextremes.
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General Tips for Calibrations-Omniscan
Sharp jagged triangular dropoutsin green line trace- usually couplantdependant- check couplantbetween wedge and block first- if itrepeats at the same angle everytime after reapplying couplant, it ismore than likely between the wedgeand probe- reapply couplant here.
Can also be gating-look at scan toset gates over the entirety of thereflector through all the angles.
Sharp diagonal dropout- completeloss of couplant or insufficientamplitude- view ascan at point ofdropout- reapply couplant, increasegain, lower gate threshold toencompass ascan amplitude.
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General Tips for Calibrations-Omniscan
Data cursor tracks to other reflectornot being used for calibration-examine and reposition gate, usecalibrate by section feature, usedifferent block.
Unable to perform wedge delay or
improper wedge delay- if everythingelse fails, observe a single reflectorin a true depth scan- the reflectorshould not drift in depthdramatically- if it does there isprobably an error in the wedge fileparameter- Probe/Part-Wedge-check if proper wedge is selected
and note the wedge settings-especially height- consult atechnical support specialist ordatabase of wedge parameters.
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Calibrate by Section
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Omniscan Error Messages during Calibration-
Sensitivity
-At least one context has an amplitude
peak greater than 100%. The calibrationcannot be performed (sensitivitycalibration) -at least one angle or vpa isgreater than the reference amplitudeyou set. Reduce gain until all beams fallbelow the high tolerance line but stillabove about 10% FSH.
-at least one context has an amplitudepeak of 0%.The calibration cannot beperformed or At least one context hasno amplitude peak in gate A. Wedgedelay calibration cannot be performed..
at least one angle or vpa is not beingpicked up due to low amplitude-increase gain, troubleshoot couplant etc
as needed Other cause of the above two errors-not
completing the edges (first/last angles/vpas)- green line may appear to go toedges, make sure you run the whitetrace line completely off screen andbeyond.
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