Why do you use a delay line with a single element transducer when measuring thin materials using an Elcometer PTG Ultrasonic Precision Thickness Gauge? How do you choose the correct length and material of delay line to measure with?
When it comes to measuring thin materials with pinpoint accuracy, the Elcometer PTG6 and PTG8 Ultrasonic Precision Thickness Gauges are designed to provide accurate, reliable material thickness measurements, on materials as little as 0.15mm thick. To do this they use a single element transducer, with a suitable delay line.
CONTENTS
0:34 - How do single element transducers work?
0:59 - Why do you use a delay line?
1:25 - Choosing the correct delay line material
1:55 - Choosing the correct delay line length
2:32 - How do you change delay lines?
When measuring thin materials with a single element transducer, the ultrasonic signal will return to the transducer incredibly quickly, and as a result there is not always enough time between the pulse leaving the element, and the echo returning. This is why, when using an Elcometer PTG, single element transducers use a delay line, to increase the time between the pulse being sent and the echo being received, ensuring more accurate results.
There are two different materials of delay line – acrylic and graphite - and the material you are measuring will affect the material of the delay line you should use. Acrylic delay lines are suitable for measuring on steel, aluminium, and titanium, with the gauge in either Interface-Echo or Echo-Echo mode; while thin plastics and other similar materials should be measured using a graphite delay line, with the gauge set to Plastic Mode.
There are also different lengths of delay line, and the one that is best suited to your application is typically dependent on the thickness and density of the material you are measuring. For example, a 12mm Acrylic delay line is best used on thicker materials and provides greater accuracy on “noisy” materials – in other words, materials that are good conductors of sound.
On the other hand, because it is shorter, a 9mm Acrylic delay line provides a greater signal strength, helping you to measure more dense materials which are tougher to penetrate, such as plastics or lead for example.
To change delay lines, with the transducer disconnected from the gauge, unscrew the knurled collar and remove it, followed by the delay line you are replacing. Before placing the new delay line onto the transducer, you should ensure there is a small amount of ultrasonic couplant between the transducer and the delay line, to aid the ultrasonic pulse in travelling freely between them.
If there is no couplant between them, or it has dried out over time, the ultrasonic pulse will not reach the delay line, resulting in no measurements. That’s why it’s always worth applying more couplant periodically, or whenever you change delay lines.
With the couplant and new delay line in place, simply replace the knurled collar, and retighten.
Next, connect your transducer to your Elcometer PTG, and switch it on. Typically, you will be automatically asked to confirm the frequency and diameter of your transducer, along with the delay line you are using, instantly. Simply select the delay line from the list in the gauge, and press the ‘OK’ softkey.
For more information on the Elcometer PTG Precision Thickness Gauges, please contact Elcometer at sales@elcometer.com, or visit our website:
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STANDARDS:
EN14127, EN15317
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