where expertise comes together - since 1996 -

The Largest Open Access Portal of Nondestructive Testing (NDT)

Conference Proceedings, Articles, News, Exhibition, Forum, Network and more

where expertise comes together
- since 1996 -
748 views
Technical Discussions
Harris Goodyear
Harris Goodyear
06:56 Aug-16-2001
eddy current probe size

My question is why do you get great depth of penetration with a large diameter probe. The reason I ask this question is becauseif you increase your probe size in fact you increase your coil inductance, with more inductance you have more XL, more XL moves you down the conductivity curve. If you use your standard depth of penetration formula, the further down the conductivity curve you go your effective depth of penetration decreases, so how in fact can you get such great penetration. ALL the eddy current formulas contradict this coil size to great penetration theory.


 
 Reply 
 
Jeff Draper
Jeff Draper
04:28 Aug-17-2001
Re: eddy current probe size
I think you are mixing up your technical information. You seem to be combining the probe design properties with the material properties. You calculate standard depth of penetration for a given material you are testing, not for the probe. The impedance change related to increased inductance is for the probe, not the material, whereas the conductivity curve is for materials, not the probe.

If you take a look at the formula for calculating the standard depth of penetration on a given material, you will notice that inductance is not part of the equation. It depends only upon the material properties (conductivity & permeability) and the frequency at which you are driving the probe.

The formula is d=50*sqrt[r/(f*rp)]
d=depth of penetration in mm
r=resistivity in milliohm-cm (equal to 172.41/%IACS) f=frequency in Hz
rp=relative permeability

The only way inductance is remotely related to this equation is through the impedance matching of the probe and the bridge. This will give you your optimal operational frequency range for a given inductance with a given bridge impedance.



 
 Reply 
 
Avi Sela
Avi Sela
09:08 Jun-20-2002
Re: eddy current probe size
I think you are mixing up your technical information. You seem to be combining the probe design properties with the material properties. You calculate standard depth of penetration for a given material you are testing, not for the probe. The impedance change related to increased inductance is for the probe, not the material, whereas the conductivity curve is for materials, not the probe.
.
: If you take a look at the formula for calculating the standard depth of penetration on a given material, you will notice that inductance is not part of the equation. It depends only upon the material properties (conductivity & permeability) and the frequency at which you are driving the probe.
.
: The formula is d=50*sqrt[r/(f*rp)]
: d=depth of penetration in mm
: r=resistivity in milliohm-cm (equal to 172.41/%IACS) f=frequency in Hz
: rp=relative permeability
.
: The only way inductance is remotely related to this equation is through the impedance matching of the probe and the bridge. This will give you your optimal operational frequency range for a given inductance with a given bridge impedance.
.



1
 
 Reply 
 
Tomasz Piech
Tomasz Piech
09:36 Jun-20-2002
Re: eddy current probe size
: I think you are mixing up your technical information. You seem to be combining the probe design properties with the material properties. You calculate standard depth of penetration for a given material you are testing, not for the probe. The impedance change related to increased inductance is for the probe, not the material, whereas the conductivity curve is for materials, not the probe.
: .
: : If you take a look at the formula for calculating the standard depth of penetration on a given material, you will notice that inductance is not part of the equation. It depends only upon the material properties (conductivity & permeability) and the frequency at which you are driving the probe.
: .
: : The formula is d=50*sqrt[r/(f*rp)]
: : d=depth of penetration in mm
: : r=resistivity in milliohm-cm (equal to 172.41/%IACS) f=frequency in Hz
: : rp=relative permeability
: .
: : The only way inductance is remotely related to this equation is through the impedance matching of the probe and the bridge. This will give you your optimal operational frequency range for a given inductance with a given bridge impedance.
: .
.

Diese Formel ist d.h. Küche Formel", sie ist Viel zu vereinfacht. In der Tat muß man die Umrechnungen mit Hilfe sehr komplizierten (Besselschen Funktionen höherer Ordnung) berechnen. In der Ingenieurpraxis nimmt man nicht in der Acht, daß der Werkstoff stell sich als nichtlineares Material sondern linear. Magnetisch Permäabilität ist eine nichtlineare Funktion der Magnetfeldstärke und für aller Berechnungen soll man genaue Verteilung drr magnetischen Feldes zu kennen. Aber das zur Zeit unmöglich ist!


1
 
 Reply 
 
Tomasz Piech
Tomasz Piech
09:37 Jun-20-2002
Re: eddy current probe size
: I think you are mixing up your technical information. You seem to be combining the probe design properties with the material properties. You calculate standard depth of penetration for a given material you are testing, not for the probe. The impedance change related to increased inductance is for the probe, not the material, whereas the conductivity curve is for materials, not the probe.
: .
: : If you take a look at the formula for calculating the standard depth of penetration on a given material, you will notice that inductance is not part of the equation. It depends only upon the material properties (conductivity & permeability) and the frequency at which you are driving the probe.
: .
: : The formula is d=50*sqrt[r/(f*rp)]
: : d=depth of penetration in mm
: : r=resistivity in milliohm-cm (equal to 172.41/%IACS) f=frequency in Hz
: : rp=relative permeability
: .
: : The only way inductance is remotely related to this equation is through the impedance matching of the probe and the bridge. This will give you your optimal operational frequency range for a given inductance with a given bridge impedance.
: .
.

Diese Formel ist d.h. Küche Formel", sie ist Viel zu vereinfacht. In der Tat muß man die Umrechnungen mit Hilfe sehr komplizierten (Besselschen Funktionen höherer Ordnung) berechnen. In der Ingenieurpraxis nimmt man nicht in der Acht, daß der Werkstoff stell sich als nichtlineares Material sondern linear. Magnetisch Permäabilität ist eine nichtlineare Funktion der Magnetfeldstärke und für aller Berechnungen soll man genaue Verteilung drr magnetischen Feldes zu kennen. Aber das zur Zeit unmöglich ist!
mei e-mail war unkorrekt!
Richtig: piech@arcadia.tuniv.szczecin.pl

Bitte um Entschuldigung!


1
 
 Reply 
 

Product Spotlight

OmniScan™ X3 flaw detector

The OmniScan X3 flaw detector is a complete phased array toolbox. Powerful tools, like total focus
...
ing method (TFM) images and advanced visualization capabilities, enable you to complete your inspection with greater confidence.
>

GEKKO - Portable Phased Array Testing with TFM in Real-Time

The portable phased array testing system GEKKO provides 64 parallel test channels. On creating testi
...
ng parameters the operator is assisted by the CIVA software. Due to its modular set-up the GEKKO instrument is suitable for operators of all skill levels.
>

Semi-Automated Phased Array Immersion System for Small Composite Parts

Turn-key semi-automated system as an improved and affordable solution for inspection of small comp
...
osite parts. Includes support table, immersion tank, scanner, PA instrument, PC, Analysis software, database, wedge management and other options.
>

MUSE Mobile Ultrasonic Equipment

The MUSE, a portable ultrasonic imaging system, was developed for in-field inspections of light-weig
...
ht structures. The MUSE consists of a motor-driven manipulator, a water circulation system for the acoustic coupling and a portable ultrasonic flaw detector (USPC 3010). The MUSE provides images of internal defects (A-, B-,C- and D-scan).
>

Share...
We use technical and analytics cookies to ensure that we will give you the best experience of our website - More Info
Accept
top
this is debug window