where expertise comes together - since 1996 -

# The Largest Open Access Portal of Nondestructive Testing (NDT)

Conference Proceedings, Articles, News, Exhibition, Forum, Network and more

where expertise comes together
- since 1996 -
 477 views
Technical Discussions
Alex
,
Israel, Joined Sep 2017, 8

Alex

,
Israel,
Joined Sep 2017
8
08:35 Dec-11-2019
Influence of pulse frequency on measurement of material thickness change

Hi guys,

I'm a bit confused with the following question. Assuming the signal sampling frequency is sufficiently high, how the ultrasonic pulse frequency influences the measurement precision of material thickness change in a pulse-echo mode?

The example of the problem is this. Material with c=3.4 mm/microsec is grinded by a 0.1 mm steps from top to bottom, signal sampling frequency is very high (1.25 GHz) and the frontwall and backwall echoes are clearly visible. What is the basic difference if a transducer with 1MHz, 2.25 or 3.5 MHz or higher is used for that?

Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 786

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
786
11:02 Dec-11-2019
Re: Influence of pulse frequency on measurement of material thickness change
In Reply to Alex at 08:35 Dec-11-2019 (Opening).

No difference, but you got to use zero crossing method.

Wiesław Bicz
Engineering,
PBP Optel sp. z o.o., Poland, Joined Feb 2009, 272

Wiesław Bicz

Engineering,
PBP Optel sp. z o.o.,
Poland,
Joined Feb 2009
272
12:38 Dec-11-2019
Re: Influence of pulse frequency on measurement of material thickness change
In Reply to Alex at 08:35 Dec-11-2019 (Opening).

Time of flight measurement has not much to do with frequency, but with the method of signal analysis. This was already discussed on this forum many times. Frequency of signal is of much lower importance than for example the accuracy of amplitude measurement.
Zero crossing method mentioned by Anmol is one of the simplest possibilities.

Alex
,
Israel, Joined Sep 2017, 8

Alex

,
Israel,
Joined Sep 2017
8
14:16 Dec-11-2019
Re: Influence of pulse frequency on measurement of material thickness change
In Reply to Wiesław Bicz at 12:38 Dec-11-2019 .

Hi Anmol and Wieslaw, thank you for your response.
I use envelope extraction and cross-correlation to estimate the time of flight. And use this method consistently between all acquired signals on the course of material thickness change.

Can you though, describe why the pulse wavelength has nothing to do with the distance change measurement? Can I measure smaller and smaller increments of the thickness change only by carrying for sufficiently high sampling period?

Wiesław Bicz
Engineering,
PBP Optel sp. z o.o., Poland, Joined Feb 2009, 272

Wiesław Bicz

Engineering,
PBP Optel sp. z o.o.,
Poland,
Joined Feb 2009
272
18:08 Dec-12-2019
Re: Influence of pulse frequency on measurement of material thickness change
In Reply to Alex at 14:16 Dec-11-2019 .

There are two critical factors in TOF measurement:
The most important factor is the accuracy of amplitude measurement.
In the case if you want to measure the distance to some pulse measured from the excitation moment, the synchronization between the pulser excitation and sampling clock is also critical.
In the case of measurement between two pulses practically only the accuracy of amplitude measurement. Sampling rate must be sufficient from the point of view of Nyquist criterion, but is of significantly lower importance than the amplitude measurement accuracy.
And naturally the algorithm, that calculates this is very important and the final result depends on its quality.
If you are interested in checking this, I can send you a simple paper, where I have explained this.

Alex
,
Israel, Joined Sep 2017, 8

Alex

,
Israel,
Joined Sep 2017
8
08:31 Dec-15-2019
Re: Influence of pulse frequency on measurement of material thickness change
In Reply to Wiesław Bicz at 18:08 Dec-12-2019 .

Thank you Wiesław, I will be happy to get the paper.

Alex
,
Israel, Joined Sep 2017, 8

Alex

,
Israel,
Joined Sep 2017
8
08:58 Dec-15-2019
Re: Influence of pulse frequency on measurement of material thickness change
In Reply to Wiesław Bicz at 18:08 Dec-12-2019 .

Wiesław,
Even if I fulfill the minimum Nyquist criterion and have 10 bit vertical range, the sampling points won't fall each on the maximum of two received pulses. Why do you state that for the time of flight measurement the sampling frequency is of much lower importance?

Wiesław Bicz
Engineering,
PBP Optel sp. z o.o., Poland, Joined Feb 2009, 272

Wiesław Bicz

Engineering,
PBP Optel sp. z o.o.,
Poland,
Joined Feb 2009
272
12:23 Dec-16-2019
Re: Influence of pulse frequency on measurement of material thickness change
In Reply to Alex at 08:58 Dec-15-2019 .

If you are too close to Nyquist criterion it will be necessary to take in account not only one, but many points - correlation would be the best solution. If you have sampling rate that is more than 3 times higher in many cases only two points (with good SNR): one before zero transition and one above.

Product Spotlight

#### HARDNESS TESTER TKM-459CE combi

TKM-459CE combi applies 2 methods of hardness control: UCI and Leeb. It provides high-accuracy tes
...
ting of metals and alloys as well as items of different sizes and configurations, their hardened layers and galvanic coatings. Device represents results in HB, HRC, HV and others. Shock-, dust- and water-proof housing with intuitive software make this gauge easy to use in all working conditions.
>

#### TraiNDE UT

TraiNDE UT is a virtual tool associated with a signal database which simulates real inspection con
...
ditions for numerous applications (Type A/V1 block, DAC block, welds and plates).
>

#### Customized Probes and Transducers

With a strong development department and our own piezocomposite production, we accompany you from th
...
e first product idea to serial production. Our scientists are continuously researching new methods in the field of ultrasonic measurement technology. The progress achieved enables us to offer you optimal solutions.
>

#### ISAFE3 Intrinsically Safe Sensor System

ISAFE3 intrinsically safe sensor system of Vallen Systeme is especially targeted at the petrochemica
...
l - as well as oil and gas transportation industry. The sensor system is designed for permanent monitoring or periodic inspection tasks. Sensors are available for different AE-frequency ranges optimized for corrosion and fatigue crack detection and other applications. The ISAFE 3 sensor system consists of an AE-sensor (model ISAS3) certified according to ATEX/IEC for installation in zone 0, gas group IIC, IP68, 20 to +60 °C, and a signal isolator (model SISO3) certified for installation in zone 2. An ISAS3 sensor can be mounted in atmosphere or submerged, e.g. in water or crude oil. It is supported by mounting tools for temporary (magnets) or permanent (welded) installation. ISAFE3 supports automatic sensor coupling test and can be used with any AE signal processor supporting 28V supply at 90 mA peak, e.g. Vallen Systeme ASIP-2/A.
>

Share...
We use technical and analytics cookies to ensure that we will give you the best experience of our website - More Info
Accept
top
this is debug window