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BASIC FUNCTIONAL CONTROLS OF: Ultrasonic Flaw Detector
For Reference only
Ultrasonic Flaw Detector Modsonic Made
KEYPAD INSTRUMENTATION
UFD’s make use of menu sections that are adjusted from push-button keypads instead of knobs and toggle switches. The keypads and menus allow for the adjustment of all functions required for the standardization of the instrument in preparation for the actual test.
POWER – ON/OFF CONTROL
It is usually a press button. It starts or stops the flow of
power to the unit’s components, enabling or stopping the operation.
Almost all of the UFD Systems today use Lithium-Ion battery
pack battery sources for power to make the instrument portable.
Battery Status Indicator is used to indicate the amount of
power left in the instrument for example in the above figure When all the three
cells are displayed empty, then the battery needs to be recharged.
PROBE MODE CONTROL
There are two modes for operation in a UFD that are:
Single – used for normal and angle probes
Dual – used for TR probe
probe with applicable Mode
In single probe mode, the instrument sends and receive short
bursts of electrical energy through a co-axial cable to a single transducer.
When switched to dual-probe mode, the instrument directs
outgoing electrical bursts through the coaxial connector toward one transducer.
The transmitter is tasked with sending ultrasonic waves into the test object.
Reflected incoming signals from the material are received by a separate transducer (Receiver) connected to the coaxial connector. This results in a through transmission or dual probe test, where the sending is isolated from the receiving transducer.
RANGE CONTROL
The range control enables the technician to set a visible
A-scan screen range. Generally, the range should be set so the echo from the
thickest range material will be displayed on the screen.
Successive presses of the range key toggle through present
range values or the slewing keys can be held down to finely adjust the range
setting.
ZERO OFFSET CONTROL
The zero control compensates for sound transmission delays
associated with the transducer, cable, and Couplant. This is a subtracted time
data described below.
Electric zero: point in time when the pulser fires the
initial pulse to the transducer.
Acoustic Zero: point in time when the sound wave enters the
test object.
VELOCITY CONTROL
The velocity control adjusts the instrument’s settings to
match the speed of sound in the test object. Velocity variables are related to
Material density and elasticity,
Material temperature
mode.
i.e. longitudinal wave versus shear wave, affect the
velocity of sound within a given material.
This control allows the technician to adjust the ultrasonic
instrument based on the chosen mode of transmission, as well as the true
velocity of that mode within the test object.
Moreover, we know there are
many types of waves out of which most commonly used are
Longitudinal waves or Compression Waves: Propagation of
waves in a straight direction.
Transverse Waves or Shear Waves: particle vibrations are at
a right angle to the direction of wave propagation. Propagates in solid only.
These waves have a velocity approximate 50% of longitudinal waves.
QUICK TIP: NORMAL PROBE AND TR PROBE TRANSMIT
LONGITUDINAL WAVES AND ANGLE PROBE TRANSMITS TRANSVERSE WAVES. HENCE YOU WILL
HAVE TO CHANGE THE ALSO AS PER THE PROBE USED.
THE BELOW TABLE PROVIDES VELOCITY VALUES FOR DIFFERENT
MATERIALS FOR LONGITUDINAL AND TRANSVERSE WAVES.
Sound Velocity in Different Materials.
Instrument gain controls connect to the amplifier and adjust
the amount of amplification that incoming signals from the transducer receive
before the screen display is made.
The gain key controls
the amplifier circuit. It does not have any influence over the outbound pulses,
but the has everything to with signals returning from the test material.
The gain or system sensitivity, in modern ultrasonic instruments, may exceed 100dB and is adjustable in increments as small as 0.1dB. to use the gain control in the figure , the technician would simply press the decibel key(dB) and then the so-called slewing key(+/-) to increase decrease the amplification.
COARSE RANGE, FINE RANGE, AND DELAY CONTROLS
These controls serve as a means of causing the instrument
screen to adjust the display along the horizontal axis. This display axis
usually shows the time, distance or depth of ultrasonic travel in the test
object.
The coarse range and fine range controls are sometimes
called material calibration or material velocity controls, depending on the
manufacturer of the instrument. These controls allow the technician to perform
a basic part of the standardization/calibration of the instrument.
Coarse range and fine range controls allow for the precise
screen placement of signals from known reference distances with standardization
blocks. By the use of these controls, as well as the delay control, signals
from known distances are placed in their correct position on the display
screen.
This enables the screen to represent the appropriate
distance that will allow for complete through dimension testing. By the use of
standardization blocks made of a material like that to be tested, the
instrument screen can be set to represent 2.5,13,25 cm or more of sound travel
within test objects.
DISPLAY STATUS CONTROL
The display/status control allows the technician to switch
between views of the display screen. For example, the screen would display the
A-scan, the instrument settings or a combination of both shown on a so-called
split-screen, the figure below shows what the technician sees after pressing
the display/status button a second time.
example of Display status control
REJECT CONTROL
The purpose of the reject control in Ultrasonic flaw
detector (UFD)is to eliminate unwanted, low-level A-scan signals. It is
particularly useful in the inspection of typically coarse-grained castings.
This control works on the amplifier circuit.
GATED ALARM
In Ultrasonic flaw detector’s (UFD) Gated alarm units enable automatic alarms when discontinuities are detected. This is accomplished by setting up specific, gated or zoned areas within the test object. Signals appearing within these gates may be monitored automatically to operate visual or audible alarms. These signals may be also be passed to recorders and external controls devices, Gated alarm units usually have three controls.
Delay or Gate start: The gate start or delay control is used
for adjustment of the location of the leading edge of the gate on the display
screen.
width or Gate length: the gate length or width control is
used for adjustment of the length of the gate or the location of the gate
trailing edge.
sensitivity or Gate alarm level: The alarm level or
gate-level control is used for adjustment of the gate vertical threshold to
turn on signal lights or to activate an alarm relay.
Example of gate control, Reject & Monitor LED’s in
A-scan
DAC CURVE
In an Ultrasonic flaw detector (UFD) DAC curve stands for
the DISTANCE AMPLITUDE CORRECTION curve. It is sometimes also called TIME
CORRECTED GAIN OR TIME VARIED GAIN.
DAC Curve
CALIBRATION
The first step in any Ultrasonic test is to calibrate the instrument system to ensure proper performance. A predictable and reproducible response to known reflectors of different sizes and depths within the calibration standard must be demonstrated before any actual application to the test object can begin.
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