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- since 1996 -
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Technical Discussions
Biju Varghese
Biju Varghese
06:54 Aug-19-2005
Near Field for TR Probes

How to calculate Near Field lenght for TR Probes?


 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1281

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1281
05:23 Aug-29-2005
Re: Near Field for TR Probes
Near field is a result of interference effects from the pulsed tranducer surface. Therefore the near field would apply to the transmitter. In the receive mode a piezo element is passive and sound pressure must impinge on it to generate a voltage indicated as the "received signal" so the interference effects associated with the near field are not applicable.

Assuming a single element for each of the transmit and receive sides of the probe, the near zone calculation should apply using the standard calculations for the transmitter element only.

Ed

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: How to calculate Near Field lenght for TR Probes?
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 Reply 
 
Devendra
Devendra
18:50 Dec-25-2014
Re: Near Field for TR Probes
In Reply to Ed Ginzel at 05:23 Aug-29-2005 .

it means that near field is not applicable for TR and Normal proble please ensure me sir.

 
 Reply 
 
Shank Vagal
India, Joined Jun 2014, 73

Shank Vagal

India,
Joined Jun 2014
73
23:57 Dec-25-2014
Re: Near Field for TR Probes
In Reply to Biju Varghese at 06:54 Aug-19-2005 (Opening).

In case of a TR probe you have no near field nor any dead zone. you can start reading from zero of the scale.

 
 Reply 
 
mark
mark
00:26 Dec-26-2014
Re: Near Field for TR Probes
In Reply to Devendra at 18:50 Dec-25-2014 .

Ed is right and I want to add some thing more,
TR probes has focal spot and and it is adjustable with roof angle of transmitter and receiver crystal by manufacturer design to get maximum response of reflector at desire focal point.focal spot is also affecte by near field of each crystal and as you know there is maximum response at the end of nearfield of single crystal so focal spot should be set at end of near field of transmitter crystal by manufacturers.you can measures focal spot for TR probes and near field for single probes by making DAC curve with special reference block.

 
 Reply 
 
John Brunk
Engineering, NDT Level III
Self employed, part-time, USA, Joined Oct 1999, 161

John Brunk

Engineering, NDT Level III
Self employed, part-time,
USA,
Joined Oct 1999
161
03:43 Dec-29-2014
Re: Near Field for TR Probes
In Reply to Shank Vagal at 23:57 Dec-25-2014 .

Although a TR probe does not exhibit a near field, it may have a dead zone. A small reflector such as a corrosion pit that is too close to the test surface will not necessarily produce a reflection that is well detected by the receiving element. Some TR probes are stated by the manufacturer to have an optimum range, with the minimum and maximum useful limits being somewhat beyond these. If the object is to measure very thin sections a single-element probe with a delay line may be better. But with this type of probe there is less sensitivity to corrosion pits because the beam is spreading beyond the near field, where with a TR robe the beam has effectively a focused zone.

 
 Reply 
 
John Norman
Consultant, owner of business
NTS Ultrasonics Pty Ltd, Australia, Joined Oct 2012, 114

John Norman

Consultant, owner of business
NTS Ultrasonics Pty Ltd,
Australia,
Joined Oct 2012
114
09:44 Dec-29-2014
Re: Near Field for TR Probes
In Reply to Biju Varghese at 06:54 Aug-19-2005 (Opening).

Hi Biju.

Mark is correct in that a good way to work it out is to generate a DAC curve for the probe. My concern with calculation based on the transmitter element is that TR probe elements usually have a complex shape, often a "half moon" or something like that. Nearfield calculations using simple text book formula are a bit difficult to apply, even for TR probes with rectangular elements.

Regards
John Norman

 
 Reply 
 
Anderson Hwang
Sales, - -
Guangdong Goworld Co., Ltd., China, Joined Sep 2010, 8

Anderson Hwang

Sales, - -
Guangdong Goworld Co., Ltd.,
China,
Joined Sep 2010
8
03:42 Dec-31-2014
Re: Near Field for TR Probes
In Reply to Biju Varghese at 06:54 Aug-19-2005 (Opening).

Dear Sir,

Yes, the peers above my "floor" are all right. And I think both DAC and DGS are OK. DGS might be simple to witness.

 
 Reply 
 

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