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Here is something that I do frequently when I get a new wedge/probe combination. In most cases, things are as they should be, some sometimes they are not. When the probe pitch, wedge/water velocity, wedge angle, and height to first element are correct, the results should be that all elements are firing perpendicular to the surface (be it Rexolite or plate if immersion) and they should start at 0.000in. That is, the leading flank of the first signal should be at 0.000. Here's what I do to check this:

Create a Focal Law calculator with an Aperture of 1 and zero degree (stop element that of the probe). Adjust the start of the A-Scan to -0.100in and zoom in ... set Reference UT Cursor to 0.000 and look to see if they are flat and start at 0.000.

http://img103.imageshack.us/img103/7457/sa2n45s2l64a2defaulttz1.gif

Above is a link to a SA2-N45S wedge with a 2L64-A2 probe. Notice the leading flank of the A-Scan is at 0.000in and the elements are flat across the face. If something is wrong, you will see it as not being flat or as in the case below, the height not starting at 0.000.

http://img218.imageshack.us/img218/7268/sa2n60l2l64a2defaultrf1.gif

In this image above, this is a SA2-N60L wedge with a 2L64-A2 probe. Same setup as described, but notice that the elements do not start at 0.000in. It appeared that it was off by approximately 0.015in. The blue line in the S-Scan should touch the red Reference cursor at 0.000in. The depths are all wrong and calibration on a NAVSHIPS block is very difficult. I am attempting to Define a wedge that will help this ...

I do the same type procedure to check out Immersion type setups with water wedges on the FOCUS LT also. I think it is a good idea to have a look ultrasonically to see if the parameters are correct. The setup with the first link above (SA2-N45S) calibrated beautifully with surface distances spot-on from 0.500in to 1.500in SDH and the depths had a delta of +0.007in/-0.009in. Average depth delta was about 0.15mm which I think is pretty good!

The most important parameters I've found for a great calibration are:

Probe Pitch
Wedge Angle
Wedge Velocity
Height to First Element

Once these values are set/verified Material Velocity is the next thing I look at.

_____________________________
NAS-410 Level III UT
Phased Array Ultrasonic Testing

Well, to reply to my own post ...

I am currently taking a two week course on the OmniScan MX, offered by an affiliate of Olympus NDT: Davis NDT, Inc. So far, I am very pleased with the content and applications.

I was also happy to notice today in class that there was an exercise which utilized the "... aperture of 1 / 0 degree" to check out the probe/wedge combination. That is the same thing I described above that I do with the FOCUS LT & TomoView ... as little (or as much) as the OmniScan can relate to the FOCUS LT, there really is justification for checking out probe parameters if one is trying to extract as precise of measurements as possible.

As with the OmniScan, I take it as far as zooming in to see exactly how far off - or how precise - the Height to First Element is set in relation to 0.000 in(mm). That's a bit nit-picky, I know, but it's something I do in the lab environment. I was happy to see that this was somewhat incorporated into the class teachings as well!

If you are a "tweaker" this is fun stuff!

_____________________________
NAS-410 Level III UT
Phased Array Ultrasonic Testing

Thanks for the feedback, Jeff. It's always nice to hear good feedback about our training Partners, especially as training is really the limiting factor for phased arrays.

As for your new exercise, it definitely falls into the advanced level for OmniScan users, but looks like fun. So, thanks again for the feedback, but it may not be appropriate to add this to the standard OmniScan courses yet.

Michael

[quote=Jeff]Well, to reply to my own post ...

I am currently taking a two week course on the OmniScan MX, offered by an affiliate of Olympus NDT: Davis NDT, Inc. So far, I am very pleased with the content and applications.

I was also happy to notice today in class that there was an exercise which utilized the "... aperture of 1 / 0 degree" to check out the probe/wedge combination. That is the same thing I described above that I do with the FOCUS LT & TomoView ... as little (or as much) as the OmniScan can relate to the FOCUS LT, there really is justification for checking out probe parameters if one is trying to extract as precise of measurements as possible.

As with the OmniScan, I take it as far as zooming in to see exactly how far off - or how precise - the Height to First Element is set in relation to 0.000 in(mm). That's a bit nit-picky, I know, but it's something I do in the lab environment. I was happy to see that this was somewhat incorporated into the class teachings as well!

If you are a "tweaker" this is fun stuff!

_____________________________
NAS-410 Level III UT
Phased Array Ultrasonic Testing[/quo

Jeff:

Thanks for the suggestion. Maybe it's a good idea to add this, but hopefully the training companies will read this site periodically and decide to add their own (like Davis NDE). We have a policy of supplying the companies with material, then letting them do what they know how to do (set up training courses and train). The alternative is for Olympus NDT to post an appropriate application note on our Training Extranet site. Of course, NASA is a very high-end user, so it may be that many applications do not require the quality that you do, i.e. fractions of a millimetre accuracy.

Michael Moles