How to choose the correct Delay Line for your Elcometer PTG Ultrasonic Thickness Gauge
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.
When triggered by a voltage, single element transducers emit an ultrasound pulse, and it travels from the transducer, into the material aided by ultrasonic couplant, hits the back-wall of the material, and echoes back towards the transducer where it is detected. The gauge then uses the speed of the pulse, and the time taken between the pulse being emitted and the echo being detected, to calculate the thickness of the material.
However, measuring thin materials means that 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.