Ultrasonic Flaw Detector Modsonic Made1
EQUIPMENT USED IN ULTRASONIC TESTING
Each NDT Method is a vast subject and hence can’t be covered in one Article hence we will be learning about each method in multiple articles so that the articles don’t become overloaded and too long to refer and study. In this Article Equipment used in Ultrasonic Testing, we will learn about different equipment used in Ultrasonic Testing.
Their internal components
Their function and role in the Ultrasonic test.
DEFINITIONS
Pulse is a short wave train of mechanical vibrations.
ULTRASONIC FLAW DETECTOR
It generates and displays an ultrasonic waveform that is interpreted by a trained NDT operator, often with the aid of analysis software, to locate and categorize flaws in test pieces.
Ultrasonic flaw detector Block Diagram
It typically includes an ultrasonic Pulser/receiver, hardware and software for signal capture and analysis, a waveform display, and a data logging module.
POWER SUPPLY
Electrical power is provided from the line of supply or from a battery in the case of Portables UFD.
Usually controlled by on/off switch and a fuse.
Time delay devices protect the circuit elements during instrument warm-up.
Circuits to supply power in all the components.
TRANSDUCER
A transducer is a device that converts energy from one form to another.
An ultrasonic transducer consists of a thin piezoelectric disk and its holder.
The piezoelectric disk converts the electrical energy to ultrasonic energy and introduces vibrations into the test object.
It also reflected ultrasonic vibrations from within the test object and converts them into electrical signals for amplification and display
PULSER/ RECEIVER
The pulser/pulse generator is the source of short high energy bursts of electrical energy (triggered by timer) that are applied to the transducer.
Reflected pulses from the test object are received by the transducer, sent to the receiver, amplified and routed to the display unit.
The amplifier amplifies the received signal from the transducer which can be calculated using the equation.
Where H2 and H1 are different echo heights
SWEEP GENERATOR:
it sets a horizontal line (Time baseline) on the display to represent the thickness of the test item. HH and VV are two sets of electrodes. If voltage is applied on HH(Horizontal Deflection Plates)plates the beam will deflect horizontally and a voltage on VV(Vertical deflection Plates) plates will deflect the beam vertically.
DISPLAY AND TIMER:
In today’s ultrasonic testing devices flat panel display screens are used. Earlier in the 1990s oscilloscope cathode ray tubes were used. In both types of display, units are interrogated with a sweep generator and the controls required to provide a visual image signal received from the object.
TRANSDUCERS/PROBE/SEARCH UNIT:
a device that converts variations in a physical quantity, such as pressure or brightness, into an electrical signal, or vice versa. It is an essential component in ultrasonic testing. It is a combination of several elements performing many functions.
FREQUENCY OF PROBES:
Frequency (pulse repetition): the number of times per second an electro-acoustic search unit is excited by the pulse generator to produce a pulse of ultrasonic energy. This is also called the pulse repetition rate.
Higher the frequency, greater the sensitivity, and resolution, but attenuation is also greater and the penetration is poor.
Lower the frequency, deeper the penetration, and less the attenuation but greater beam spread, less the sensitivity, and resolution.
The sensitivity of a transducer is given by
TYPES OF PROBE:
NORMAL PROBE
It used to transmit longitudinal waves into the test object.
Here single transducer acts as both transmitter and receiver.
Dia. 10mm, 4 MHz and Dia 24mm, 2 MHz are general-purpose Normal Probes.
It can be used for raw material inspection, an inspection of slightly rough thickness. It is not advised to use the normal probe for very thin components because of the dead zone.
The dead zone is a zone where it is not possible to detect defects. Spherical waves interfere with each other and result in a system of maxima and minima in intensity in the region close to the transducer. This region is known as the near field region or Fresnel zone
TR (TRANSMITTER/RECEIVER) PROBE:
Used to transmit longitudinal waves into the test object.
It is a dual crystal transducer useful to test objects that are of relatively less thickness(less than 25mm) since it doesn’t have any dead zone.
One crystal acts as a transmitter and other act as a receiver.
Dia 10 mm, 4 MHz and Dia 24 mm, 2 MHz are commonly used TR probes.
Schematic Diagram of TR Probe
ANGLE PROBE:
When the ultrasonic beam incident at an angle to the interface the reflected wave is also at an angle to the surface.
When the ultrasonic beam incident at an angle, the transmitted beam undergoes an abrupt change in the direction and this phenomenon is called Refraction.
Angle probe is used for inspection of plates, castings, and welds.
COAXIAL CABLES:
Co-axial Cable
CONNECTORS ARE ATTACHED AT BOTH ENDS OF CO-AXIAL CABLE AND CONNECT THE UFD WITH PROBE
COUPLANT
If a transducer is placed in contact with the surface of a dry object, very little energy is transmitted through the interface into the material because of the presence of air between the transducer and test material.
The surface finish of the test specimen.
The temperature of the test specimen.
Possibility of chemical reactions between the test specimen and the couplant.
Cleaning requirement
Position of the test specimen.
Commonly used Couplants are glycerin, water, oils, petroleum greases, silicone grease, and other commercial pastes.
Above mentioned all types of equipment are basic equipment important to carry out Ultrasonic Testing of a material.
One more important thing is calibration of Equipment using calibration Blocks about which we will learn in the next article for Ultrasonic testing.