A much simpler and cheaper solution is to use a gauge with multiple echo capabilities. Multiple echo gauges measure just the metal substrate and completely ignore coatings up to 20mm thick, depending on the coating type and as long as they are solidly adhered to the surface. They work by ‘looking’ at three or more consecutive ultrasound pulses. The first returned echo is used as a reference and the subsequent echoes are used to measure just the metal thickness. A reading is only given if these are equal, which ensures the gauge is definitely measuring to the back wall and not a pit or flaw in the material. Multiple echo gauges also do not require zeroing before use.
3. ULTRASONIC PROBES
There are two common types of probes used with ultrasonic thickness gauges. These are twin crystal and single crystal probes. Twin crystal probes have a separate transmit and receive crystal on their face, which are angled towards each other, resulting in a ‘V’ shape ultrasound path. The ‘V’ shape means that the probe has to be in a certain orientation on curved or round surfaces, such as pipelines, because the angle at the bottom is otherwise affected. This is also the case over varying measuring ranges and corrections are often programmed into the gauge to compensate.
Single crystal probes however, as their name implies, have a single crystal which transmits and receives the ultrasound pulse. The ultrasound travels straight up and down ensuring there is no V-beam error, and it means they have a linear accuracy throughout their measuring range. Single crystal probes can be rotated through 360° without any change in measurement accuracy, even on curved surfaces. This is essential when using a gauge on a drone because it is very difficult to always ensure the orientation of the probe on the surface being measured.
All probes manufactured by Tritex NDT have a microchip installed which contains specific information relating to the probe, such as its sensitivity, gain setting and frequency. This information is transferred to the gauge when the probe is connected, resulting in a perfectly matched probe and gauge combination for improved performance.
4. MULTIGAUGE 6000 DRONE THICKNESS GAUGE
Multiple echo is therefore ideally suited for using on a drone because coatings do not have to be removed. This also means that probes can have protective membranes on their face which in no way affect the accuracy of the measurment. The Multigauge 6000 Drone Gauge takes advantage of this with the addition of a special membrane material which allows measurements to be taken without the need for wet couplant. However, the dry couplant membrane does have some limitations in that extra pressure has to be applied and it is only suitable for use on smooth surfaces.
For this reason, Tritex NDT have also developed a gel dispenser which is controlled wirelessly from the dedicated communicator software. Simply clicking on the button within the software will dispense a pre-determined quantity of gel onto the face of the probe prior to taking any measurements.
The Report • September 2018 • Issue 85 | 65
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80
