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3024 views
08:11 May-03-2007
Larry Mullins
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.


 
05:20 May-04-2007

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
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 ------------




 
06:36 May-04-2007

J. Mark Davis

Teacher, And Consultant
University of Ultrasonics, Birmingham, Alabama,
USA,
Joined Mar 2000
83
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 ------------




 
07:06 May-04-2007

Linxiao Yu

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




 
09:39 May-04-2007

Rocky

Engineering
Milky Way Jewels,
USA,
Joined Nov 1998
40
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 ------------



 
01:31 May-29-2007

David Mackintosh

Engineering,
Acuren Group Inc.,
Canada,
Joined Feb 2011
85
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 ------------




 
01:02 Jun-02-2007
Andreas Voge
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.




 
01:14 Jun-02-2007
Ken Beck
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?


 
01:43 Jun-02-2007

John Brunk

Engineering, NDT Level III
Self employed, part-time,
USA,
Joined Oct 1999
157
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.



 


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