Ultrasonic Thickness Gauges are capable of non-destructively measuring a wide variety of materials, when only one side is accessible.
Ultrasonic NDT Thickness Gauges are ideal for, among other things, monitoring corrosion and erosion, or checking for defects in complex, manufactured components.
This video explains how the Dakota CX and PCX Ultrasonic NDT gauges work, by explaining how Dual Element Transducers and Single Element Transducers take readings.
The video covers how the measurement modes of Pulsed - Echo (P-E), Interface Echo (I-E), Echo - Echo (E-E), and Echo - Echo ThruPaint™ Mode (E-E) all work.
CONTENTS
0:08 - What are Ultrasonic Thickness Gauges?
1:05 - How do Ultrasonic NDT Gauges Work?
2:00 - How Dual Element Transducers Work?
4:25 - How do Single Element Transducers Work?
6:33 - For More Information
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Ultrasonic distance measurement uses high-frequency sound pulses generated by a device called a Piezoelectric Transducer. These pulses travel through the material being tested and bounce back to the transducer. We measure the time it takes for the pulse to be sent and the echo to be received, also known as the ‘Time of Flight’. This time is then multiplied by the speed of sound in the material to calculate the total distance travelled. The thickness of the material is half of this distance.
The DakotaNDT CX range of ultrasonic material thickness gauges can measure both coated, and uncoated materials of up to 500mm thick.
Dual element transducers consist of two independent crystals separated by an acoustic barrier. The two elements are angled so that when one crystal emits an ultrasonic pulse, the energy path creates a “V” shape, entering the material via ultrasonic couplant, hitting the back-wall of the material and echoing towards the other crystal , where it is detected. The gauge then uses the speed of the pulse and the time taken to travel from one crystal to another i.e.,. from pulse to echo, to calculate the thickness of the material - with the acoustic barrier preventing any sound from reaching the receiver directly from the emitter, before the pulse has completed its path.
When it comes to measuring coated materials, in order to ignore the thickness of the coating and measure just the thickness of the material underneath, the gauge is adjusted to measure the time between two echoes.
The first pulse passes through the coating and echos off the boundary (which is then ignored by the gauge), that same pulse hits the back wall of the material being tested (this is the first echo), and echos back up to the transducer, with a small portion of that sound pulse bouncing off the inside of the material, into the back wall once again, and finally back up to the transducer (this is the second echo). The transducer detects both echoes and uses the speed of the pulse and time between echoes to calculate the thickness of the material, ignoring the coating above it and any other echo. This would be called Echo Echo or Through Paint
Alternatively, the Dakota PCX range of ultrasonic precision thickness gauges use single-element delay-line transducers to measure uncoated materials as thin as 0.15mm.
Single element transducers, as the name suggests, consist of one crystal which both emits and receives the ultrasound pulse. The pulse once again travels between the transducer and the material via ultrasonic couplant.
When measuring thin materials with ultrasonic signals, the quick return of the signal poses a challenge, as there may not be enough time between sending the pulse and receiving the echo. To address this, the Dakota PCX uses a delay line with single element transducers to increase the time gap and improve accuracy.
Rather than calculating the time from pulse to echo, the gauge measures from Interface to Echo. The Interface is when the pulse passes between the delay line and the material, and the Echo is when the pulse hits the back-wall of the material and returns to the transducer. By considering the time taken and the known speed of the pulse, the gauge disregards the delay line's length and accurately measures the material thickness.
For measuring extremely thin materials (as thin as 0.15mm), the Dakota PCX is adjusted to measure between two echoes. While the gauge still reads the Interface, it focuses on the time between the two subsequent echoes. The first echo occurs when the pulse hits the boundary between the coating and the material, and the second echo occurs when the pulse hits the back wall of the material. The time between these echoes, combined with the pulse speed, enables the Dakota PCX to measure very thin materials with high precision.
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For more information on the Dakota NDT CX2, visit our website:
dakotandt.com/...
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STANDARDS:
DAKOTA CX:
ASTM E797, EN 14127, EN15317
DAKOTA PCX
EN14127, EN15317
23 авг 2024
