Pulse-Echo is the basic mode: a pulse leaves, bounces off the opposite wall and comes back. The instrument times the journey and converts it into thickness. Everything else is a variation on this theme.
- ✓ Measurement of the time of flight between emitted pulse and back-wall echo
- ✓ Conversion into thickness using the material’s propagation velocity
- ✓ Access to one side of the part only
- ✓ Known limit: any coating is counted in the measurement
The transducer emits a short acoustic pulse that enters the material through the couplant gel. The pulse crosses the wall, meets the opposite surface, where the material ends and air begins, and is almost entirely reflected. The echo returns to the transducer, which converts it into an electrical signal.
What the instrument measures is therefore a time, not a length. To turn it into thickness one must know the velocity at which ultrasound propagates in that material: thickness is the product of velocity and time, divided by two, because the path is travelled twice, out and back.
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From this simplicity come both the merit and the limit of the method. The merit is that access to one side of the part is enough. The limit is that the pulse does not distinguish between different materials along its path: if there is paint on the surface, the pulse crosses it and the thickness read includes it too.
What is needed for the measurement to succeed
| Condition | Why it is necessary |
|---|---|
| Coupling between probe and surface | Without gel the interposed air reflects almost all the energy |
| Correct propagation velocity | It converts time into thickness: a wrong value skews every reading |
| Reflective opposite surface | A back-wall echo recognisable by the instrument is needed |
| Reasonably parallel faces | An inclined back wall sends the echo off the probe axis |
| Material not too attenuating | The echo must return with enough amplitude to be detected |
When Pulse-Echo is not enough
The most frequent case is the painted surface. In Pulse-Echo the reading includes metal and coating, and on a structure protected with thick coating systems the difference is not negligible. The answer is the Echo-Echo mode, which ignores the applied layer.
The second case is the heavily corroded inner surface, where the back wall is no longer flat and reflects in different directions. Here dual element probes are needed and, when the reading appears unstable, a check on the A-Scan waveform.
Instruments using this mode
| Instrument | Typical use |
|---|---|
| Dakota ZX-1 | Fixed-velocity Pulse-Echo measurement, without specialist training |
| Dakota ZX-3 | Pulse-Echo with adjustable gain for difficult surfaces |
| Dakota CX2 | Entry level with preset materials |
| Dual element transducers | Dual crystal probes for corroded surfaces |
Frequently asked questions
Because the pulse travels the thickness twice: once on the way out, to the opposite surface, and once on the way back to the transducer. The measured time therefore corresponds to twice the path.
Yes. The pulse crosses the coating and the thickness read includes it too. To measure the metal alone, Echo-Echo mode is required.
The echo is reflected in a direction different from the one it came from and may not return to the transducer. On non-parallel surfaces the measurement becomes unstable or fails.
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Further information and contacts
Systems division and sensor integration partner : www.roder.it
More information about RODER SRL : about us
Contact for general information : info@roder.it
Contact for information about these products : info@roder.it
The information contained on this web page is provided for information purposes only. Although it has been compiled with the utmost care, it does not constitute a contractual offer or a binding commitment to supply. It may contain transcription, translation or typographical errors. For precise and up-to-date information, please contact our company directly.
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