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Technical Discussions
Larry Mullins
Larry Mullins
08:11 May-03-2007
Why 2.25 MHz?

It always seemed odd to me that 2.25MHz is a popular frequency for UT? What is the importance of that extra .25MHz? 1.0, 5.0, 10.0 are popualr and are round numbers. Why 2.25 and not just 2.0? Just wondering if someone can provide insight.


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

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
05:20 May-04-2007
Re: Why 2.25 MHz?
Good question, and I've wondered the same thing. My understanding -- maybe true, maybe an NDT legend! -- is that it was basically an accident of history, that an early manufacturer of ultrasonic transducers had some ceramic that was supposed to be 2 MHz but was inadvertently cut to 2.25 MHz and they marketed it as such and it became a standard frequency. Things were a little less formal in those days. I can definitely cite that Panametrics began making commercial transducers in the early 1970s and 2.25 MHz was a standard catalog frequency for us from the beginning, so this goes back more than forty years.

At the same time, Europeans were buying 2 MHz transducers from Krautkramer, and even now 2 MHz is a standard frequency in Europe but uncommon in the US.

----------- Start Original Message -----------
: It always seemed odd to me that 2.25MHz is a popular frequency for UT? What is the importance of that extra .25MHz? 1.0, 5.0, 10.0 are popualr and are round numbers. Why 2.25 and not just 2.0?Just wondering if someone can provide insight.
------------ End Original Message ------------




 
 Reply 
 
J. Mark Davis
Teacher, And Consultant
University of Ultrasonics, Birmingham, Alabama, USA, Joined Mar 2000, 85

J. Mark Davis

Teacher, And Consultant
University of Ultrasonics, Birmingham, Alabama,
USA,
Joined Mar 2000
85
06:36 May-04-2007
Re: Why 2.25 MHz?
----------- Start Original Message -----------

Here is what I tell my students from hearsay.

That 2.25 MHZ was a standard frequency to produce "X" number of wavelengths in a given material for a given materials thickness.

This is a great question.

However, to note some flaws such as IGSCC are better detected with 1.5 MHz.

: Good question, and I've wondered the same thing. My understanding -- maybe true, maybe an NDT legend! -- is that it was basically an accident of history, that an early manufacturer of ultrasonic transducers had some ceramic that was supposed to be 2 MHz but was inadvertently cut to 2.25 MHz and they marketed it as such and it became a standard frequency. Things were a little less formal in those days. I can definitely cite that Panametrics began making commercial transducers in the early 1970s and 2.25 MHz was a standard catalog frequency for us from the beginning, so this goes back more than forty years.
: At the same time, Europeans were buying 2 MHz transducers fromKrautkramer, and even now 2 MHz is a standard frequency in Europe but uncommon in the US.
: : It always seemed odd to me that 2.25MHz is a popular frequency for UT? What is the importance of that extra .25MHz? 1.0, 5.0, 10.0 are popualr and are round numbers. Why 2.25 and not just 2.0? Just wondering if someone can provide insight.
------------ End Original Message ------------




 
 Reply 
 
Linxiao Yu
R & D, NDE in Oil & Gas; Energy; Manufacturing
BP, USA, Joined Aug 2006, 13

Linxiao Yu

R & D, NDE in Oil & Gas; Energy; Manufacturing
BP,
USA,
Joined Aug 2006
13
07:06 May-04-2007
Re: Why 2.25 MHz?
Very good and interesting question. I have another hypothesis. A little calculation shows:

When Quartz was used as piezoelectric material (very likely 50 years ago), the element thickness of a 2.25MHz L-wave probe is 0.05", which is coincidently a "ROUND" number. The element thickness of a 2MHz L-wave probe is 0.05625”.
If I were the first probe designer who most likely did not have such information as which is a “popular frequency”, by nature, I may choose a design that is easier for my machinist.

*****L-wave velocity of Quartz is about 0.225”/us.


----------- Start Original Message -----------
: Good question, and I've wondered the same thing. My understanding -- maybe true, maybe an NDT legend! -- is that it was basically an accident of history, that an early manufacturer of ultrasonic transducers had some ceramic that was supposed to be 2 MHz but was inadvertently cut to 2.25 MHz and they marketed it as such and it became a standard frequency. Things were a little less formal in those days. I can definitely cite that Panametrics began making commercial transducers in the early 1970s and 2.25 MHz was a standard catalog frequency for us from the beginning, so this goes back more than forty years.
: At the same time, Europeans were buying 2 MHz transducers from Krautkramer, and even now 2 MHz is a standard frequency in Europe but uncommon in the US.
: : It always seemed odd to me that 2.25MHz is a popular frequency for UT? What is the importance of that extra .25MHz? 1.0, 5.0, 10.0 are popualr and are round numbers. Why 2.25 and not just 2.0? Just wondering if someone can provide insight.
------------ End Original Message ------------




 
 Reply 
 
Rocky
Engineering
Milky Way Jewels, USA, Joined Nov 1998, 40

Rocky

Engineering
Milky Way Jewels,
USA,
Joined Nov 1998
40
09:39 May-04-2007
Re: Why 2.25 MHz?
The story I heard from an old hand about 35 years ago was that early transducer frequencies were uncertain and were made and then tested to determine the frequency and marked accordingly. The 2.25 MHz was just the one some influencial first adopter chose to use successfully and that got incorporated into the the specification. Since the usual tolerance on frequency is 10% this would allow a center frequency of 2.03 to 2.48 MHz even then.

----------- Start Original Message -----------
: Good question, and I've wondered the same thing. My understanding -- maybe true, maybe an NDT legend! -- is that it was basically an accident of history, that an early manufacturer of ultrasonic transducers had some ceramic that was supposed to be 2 MHz but was inadvertently cut to 2.25 MHz and they marketed it as such and it became a standard frequency. Things were a little less formal in those days. I can definitely cite that Panametrics began making commercial transducers in the early 1970s and 2.25 MHz was a standardcatalog frequency for us from the beginning, so this goes back more than forty years.
: At the same time, Europeans were buying 2 MHz transducers from Krautkramer, and even now 2 MHz is a standard frequency in Europe but uncommon in the US.
: : It always seemed odd to me that 2.25MHz is a popular frequency for UT? What is the importance of that extra .25MHz? 1.0, 5.0, 10.0 are popualr and are round numbers. Why 2.25 and not just 2.0? Just wondering if someone can provide insight.
------------ End Original Message ------------



 
 Reply 
 
David Mackintosh
Engineering,
Acuren Group Inc., Canada, Joined Feb 2011, 85

David Mackintosh

Engineering,
Acuren Group Inc.,
Canada,
Joined Feb 2011
85
01:31 May-29-2007
Re: Why 2.25 MHz?
I heard from some instructor that when the US started developing UT programs they specified 2.25 in order to make it harder for Europeans to sell their 2 MHz probes in the US market.

----------- Start Original Message -----------
: It always seemed odd to me that 2.25MHz is a popular frequency for UT? What is the importance of that extra .25MHz? 1.0, 5.0, 10.0 are popualr and are round numbers. Why 2.25 and not just 2.0? Just wondering if someone can provide insight.
------------ End Original Message ------------




 
 Reply 
 
Andreas Voge
Andreas Voge
01:02 Jun-02-2007
Re: Why 2.25 MHz?
----------- Start Original Message -----------
: I heard from some instructor that when the US started developing UT programs they specified 2.25 in order to make it harder for Europeans to sell their 2 MHz probes in the US market.
: : It always seemed odd to me that 2.25MHz is a popular frequency for UT? What is the importance of that extra .25MHz? 1.0, 5.0, 10.0 are popualr and are round numbers. Why 2.25 and not just 2.0? Just wondering if someone can provide insight.
------------ End Original Message ------------
With a small calculation you will see a crystal cut to 1/4" will give you a frequency of 2.25 Mhz.




 
 Reply 
 
Ken Beck
Ken Beck
01:14 Jun-02-2007
Re: Why 2.25 MHz?
I have heartd that 2.25 MHz was selected to avoid interfering with WWV signals at 2.5 MHz - which is a logical progression as half of 5 MHz (which is of course half of 10 MHz, which is half of 20 MHz). This seems doubtful since 5, 10 and other frequencies correspond to WWV frequencies. The band widths of many early flaw detectors would have allowed them to use 2 MHz transducers as well as 2.25 MHz units so the explanation that you have heard is also doubtful. Does anyone know for sure?


 
 Reply 
 
John Brunk
Engineering, NDT Level III
Self employed, part-time, USA, Joined Oct 1999, 162

John Brunk

Engineering, NDT Level III
Self employed, part-time,
USA,
Joined Oct 1999
162
01:43 Jun-02-2007
Re: Why 2.25 MHz?
----------- Start Original Message -----------
: : I heard from some instructor that when the US started developing UT programs they specified 2.25 in order to make it harder for Europeans to sell their 2 MHz probes in the US market.
: : : It always seemed odd to me that 2.25MHz is a popular frequency for UT? What is the importance of that extra .25MHz? 1.0, 5.0, 10.0 are popualr and are round numbers. Why 2.25 and not just 2.0? Just wondering if someone can provide insight.
: With a small calculation you will see a crystal cut to 1/4" will give you a frequency of 2.25 Mhz.
------------ End Original Message ------------

Back in 1963 I was taught that 2.25 MHz resulted from an even older myth that the smallest detectable discontinuity size was 1/2 wavelength in the particular material, and a common expectation/desire/requirement was to detect discontinuities in steel that were 0.060 inch and larger. This is believable if you dig into the origins of the equally correct coil formulae for magnetic particle inspection with a coil.



 
 Reply 
 

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