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Technical Discussions
LANRE ALAPINI
NDT Inspector,
NDT TRAINING AND TESTING CENTRE HOUSTON TEXAS USA, Nigeria, Joined Nov 2008, 3

LANRE ALAPINI

NDT Inspector,
NDT TRAINING AND TESTING CENTRE HOUSTON TEXAS USA,
Nigeria,
Joined Nov 2008
3
06:49 Nov-18-2008
calibration

this kind of question could be could there be any diferent between the calibration of a single element transducer and dual element transducer


    
 
 Reply 
 
Tom Nelligan
Engineering,
retired, USA, Joined Nov 1998, 390

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
07:18 Nov-18-2008
Re: calibration
Yes, there will normally be a very significant difference in the zero offset calibration between a single element contact transducer and a dual element transducer of similar frequency and diameter. In the case of a dual, you have to zero out the pulse transit time through the internal delay line, while with a contact transducer you are zeroing out only a very thin wearplate. (Other minor factors like cable length and instrument switching delays wouldn't normally vary with transducer type.)

Material sound velocity is of course independent of tranducer type.


----------- Start Original Message -----------
: this kind of question could be could there be any diferent between the calibration of a single element transducer and dual element transducer
------------ End Original Message ------------




    
 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
00:59 Nov-19-2008
Re: calibration
Lanre

Aside form the technical differences which Tom has outlined, the philosophy of calibration must be the same no matter which tools you are using - namely, traceability, accuracy and repeatability. Before commencing calibration ensure you are familiar with all your equipment's characterisitics (read manufacturer's literature/operating manuals/technical references) and that it is undamaged and in good working order. Both the thickness meter or flaw detector, depending on which you are using) and the calibration block should bear valid calibration certificates and have passed the most recent proceduralised in-house checks as evidenced by a log record. The calibration block MUST be respresentative (very similar sound velocity) of the material which you wish to inspect/measure. You can accept equivalence within but not across material groups, e.g. low alloy steels, austenitics, aluminium, copper. Find yourself a comprehensive table of sound velocities in various materials and get to know the percentage variations.

Now the same applies whether you are calibrating single or twin crystal probes with the keywords in either case being:

TRACEABILITY, ACCURACY, REPEATABILITY.

As always watch out for careless and lazy assumptions creeping in, the major cause of disastrous measurement error.

Cheers

Nigel

----------- Start Original Message -----------
: this kind of question could be could there be any diferent between the calibration of a single element transducer and dual element transducer
------------ End Original Message ------------




    
 
 Reply 
 
LANRE ALAPINI
NDT Inspector,
NDT TRAINING AND TESTING CENTRE HOUSTON TEXAS USA, Nigeria, Joined Nov 2008, 3

LANRE ALAPINI

NDT Inspector,
NDT TRAINING AND TESTING CENTRE HOUSTON TEXAS USA,
Nigeria,
Joined Nov 2008
3
06:21 Nov-20-2008
Re: calibration
nigel, if i get you right, all things being equal theres no different between calibrating with dual element transducer and single element transducer

----------- Start Original Message -----------
: Lanre
: Aside form the technical differences which Tom has outlined, the philosophy of calibration must be the same no matter which tools you are using - namely, traceability, accuracy and repeatability. Before commencing calibration ensure you are familiar with all your equipment's characterisitics (read manufacturer's literature/operating manuals/technical references) and that it is undamaged and in good working order. Both the thickness meter or flaw detector, depending on which you are using) and the calibration block should bear valid calibration certificates and have passed the most recent proceduralised in-house checks as evidenced by a log record. The calibration block MUST be respresentative (very similar sound velocity) of the material which you wish to inspect/measure. You can accept equivalence within but not across material groups, e.g. low alloy steels, austenitics, aluminium, copper. Find yourself a comprehensive table of sound velocities in various materials and get to know the percentage variations.
: Now the same applies whether you are calibrating single or twin crystal probes with the keywords in either case being:
: TRACEABILITY, ACCURACY, REPEATABILITY.
: As always watch out for careless and lazy assumptions creeping in, the major cause of disastrous measurement error.
: Cheers
: Nigel
: : this kind of question could be could there be any diferent between the calibration of a single element transducer and dual element transducer
------------ End Original Message ------------




    
 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
06:23 Nov-20-2008
Re: calibration
Lanre, if your equipment is fitted with a single or twin option ensure that you are in the correct mode. With BOTH single and twin I would position the 1st backwall echo at zero on the timebase and the second and 3rd at 5 and 10 and then delay off so that the 1st BWE is on 5 and the 2nd on 10 (illustrative figures for compression wave only). That takes care of any delay line/perspex wedge sound path.

Tom Nelligan wrote some technical differences, i wrote that the concept of calibration is identical for both single and twin - traceability, accuracy, repeatability.

Enlighten me please Lanre, what has happened or been said that makes you concerned there may be a difference?

----------- Start Original Message -----------
: nigel, if i get you right, all things being equal theres no different between calibrating with dual element transducer and single element transducer
: : Lanre
: : Aside form the technical differences which Tom has outlined, the philosophy of calibration must be the same nomatter which tools you are using - namely, traceability, accuracy and repeatability. Before commencing calibration ensure you are familiar with all your equipment's characterisitics (read manufacturer's literature/operating manuals/technical references) and that it is undamaged and in good working order. Both the thickness meter or flaw detector, depending on which you are using) and the calibration block should bear valid calibration certificates and have passed the most recent proceduralised in-house checks as evidenced by a log record. The calibration block MUST be respresentative (very similar sound velocity) of the material which you wish to inspect/measure. You can accept equivalence within but not across material groups, e.g. low alloy steels, austenitics, aluminium, copper. Find yourself a comprehensive table of sound velocities in various materials and get to know the percentage variations.
: : Now the same applies whether you are calibrating single or twin crystal probes with the keywords in either case being:
: : TRACEABILITY, ACCURACY, REPEATABILITY.
: : As always watch out for careless and lazy assumptions creeping in, the major cause of disastrous measurement error.
: : Cheers
: : Nigel
: : : this kind of question could be could there be any diferent between the calibration of a single element transducer and dual element transducer
------------ End Original Message ------------




    
 
 Reply 
 
Tom Nelligan
Engineering,
retired, USA, Joined Nov 1998, 390

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
06:24 Nov-20-2008
Re: calibration
I believe that Mr. Armstrong and I have interpreted your original question in different ways.

Is there a difference in the "philosophy" of calibration to insure accurate depth or thickness measurements? No.

Is there a difference in specific instrument setup? Yes, due to the much greater zero offset required when using dual element versus single element transducers.

----------- Start Original Message -----------
: nigel, if i get you right, all things being equal theres no different between calibrating with dual element transducer and single element transducer
: : Lanre
: : Aside form the technical differences which Tom has outlined, the philosophy of calibration must be the same no matter which tools you are using - namely, traceability, accuracy and repeatability. Before commencing calibration ensure you are familiar with all your equipment's characterisitics (read manufacturer's literature/operating manuals/technical references) and that it is undamaged and in good working order. Both thethickness meter or flaw detector, depending on which you are using) and the calibration block should bear valid calibration certificates and have passed the most recent proceduralised in-house checks as evidenced by a log record. The calibration block MUST be respresentative (very similar sound velocity) of the material which you wish to inspect/measure. You can accept equivalence within but not across material groups, e.g. low alloy steels, austenitics, aluminium, copper. Find yourself a comprehensive table of sound velocities in various materials and get to know the percentage variations.
: : Now the same applies whether you are calibrating single or twin crystal probes with the keywords in either case being:
: : TRACEABILITY, ACCURACY, REPEATABILITY.
: : As always watch out for careless and lazy assumptions creeping in, the major cause of disastrous measurement error.
: : Cheers
: : Nigel
: : : this kind of question could be could there be any diferent between the calibration of a single element transducer and dual element transducer
------------ End Original Message ------------




    
 
 Reply 
 

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