2.a.omniscan setup - calibration for sectorial scan

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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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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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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2.a.omniscan setup - calibration for sectorial scan

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