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Technical Discussions
John Turner
John Turner
00:59 Dec-02-2004
Electrical resistance measurements

Does any one know where I can get hold of a piece of equipment called the 'AT&T Microhmeter'. This was produced 15 yrs ago for spot weld inspection (amongst other things). Unfortunately, the AT&T subsidary went into liquidation after a few years.

I would assume it may be available second-hand, or that some company is still producing a similar device.

Would be most interested to hear of what is happening in this field.

regards

John Turner


    
 
 
James Dolfi
Director
ford, USA, Joined Oct 1999, 8

James Dolfi

Director
ford,
USA,
Joined Oct 1999
8
01:40 Dec-03-2004
Re: Electrical resistance measurements
----------- Start Original Message -----------
: Does any one know where I can get hold of a piece of equipment called the 'AT&T Microhmeter'. This was produced 15 yrs ago for spot weld inspection (amongst other things). Unfortunately, the AT&T subsidary went into liquidation after a few years.
: I would assume it may be available second-hand, or that some company is still producing a similar device.
: Would be most interested to hear of what is happening in this field.
: regards
: John Turner
------------ End Original Message ------------
The subject ATT device was not effective at determining weld quality. It used a four point system where test current was injected into the surface and the voltage was measured with two probes. The resistance is not an effective method for determining welds in many materials due to several factors.

Materials will exhibit relatively good conductivity even when the fusion is not sufficient for a strong weld. Additionally, materials that are coated with zinc can be soldered together at the faying surface with zinc and exhibit good conductivity. They may also only be slightly bonded by diffusion. Resistance welds of this type will not survive even moderate impact and fatigue loads.

The risk you take is assuming a weld is good until it shows poor conductivity. In my opinion, you will only detect welds that are completely unacceptable while passing welds that are not fit for service grouped along with welds that are acceptable.

Our tests at a major automobile producer site did not show the resistance check method to be sufficiently robust for acceptance. If you are not going to test resistance spot welds then the device may be useful for other applications.

I am not aware of anyone still producing the resistivity weld checker commercially. You should be able to make one easily from commercially available equipment if you are handy designing and assembling electro-mechanical equipment. A suitable 100 A (max) power supply is available from RoMan Mfg. 861 47th St. SW, Grand Rapids, Mi 49509 Michigan, USA. The probe would have to be custom made.

The origginal unit was very portable. The power supply from RoMan will be rather large perhaps 15 kg.





    
 
 
Phil Thayer
Sales, -
MISTRAS Products & Systems, USA, Joined Feb 2002, 12

Phil Thayer

Sales, -
MISTRAS Products & Systems,
USA,
Joined Feb 2002
12
04:59 Dec-03-2004
Re: Electrical resistance measurements
John,

The AT&T resistivity line (M100 & M200) was purchased by Physical Acoustics Corp (PAC) in Princeton NJ. The aquistion was not surprising since PAC's founders were former AT&T scientists who spun off and created PAC, a very successful; Acoustics Emission, Ultrasonic & eddy current and NDT Field tesing company. The M100 is now called the M100A after a revisit by engineering last year. It is being used sucessfully in many industries and applications from weld inspection (spot & laser), material sorting, and hardness testing. For more information please visit the company web site at pacndt.com.


----------- Start Original Message -----------
: Does any one know where I can get hold of a piece of equipment called the 'AT&T Microhmeter'. This was produced 15 yrs ago for spot weld inspection (amongst other things). Unfortunately, the AT&T subsidary went into liquidation after a few years.
: I would assume it may be available second-hand, or that some company is still producing a similar device.
: Would be most interested to hear of what is happening in this field.
: regards
: John Turner
------------ End Original Message ------------




    
 
 
S.V.Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
07:11 Dec-04-2004
Re: Electrical resistance measurements
----------- Start Original Message -----------
: : Does any one know where I can get hold of a piece of equipment called the 'AT&T Microhmeter'. This was produced 15 yrs ago for spot weld inspection (amongst other things). Unfortunately, the AT&T subsidary went into liquidation after a few years.
: : I would assume it may be available second-hand, or that some company is still producing a similar device.
: : Would be most interested to hear of what is happening in this field.
: : regards
: : John Turner
: The subject ATT device was not effective at determining weld quality. It used a four point system where test current was injected into the surface and the voltage was measured with two probes. The resistance is not an effective method for determining welds in many materials due to several factors.
: Materials will exhibit relatively good conductivity even when the fusion is not sufficient for a strong weld. Additionally, materials that are coated with zinc can be soldered together at the faying surface with zinc and exhibit good conductivity. They may also only be slightly bonded by diffusion. Resistance welds of this type will not survive even moderate impact and fatigue loads.
: The risk you take is assuming a weld is good until it shows poor conductivity. In my opinion, you will only detect welds that are completely unacceptable while passing welds that are not fit for service grouped along with welds that are acceptable.
: Our tests at a major automobile producer site did not show the resistance check method to be sufficiently robust for acceptance. If you are not going to test resistance spot welds then the device may be useful for other applications.
: I am not aware of anyone still producing the resistivity weld checker commercially. You should be able to make one easily from commercially available equipment if you are handy designing and assembling electro-mechanical equipment. A suitable 100 A (max) power supply is available from RoMan Mfg. 861 47th St. SW, Grand Rapids, Mi 49509 Michigan, USA. The probe would have to be custom made.
: The origginal unit was very portable. The power supply from RoMan will be rather large perhaps 15 kg.
:
:
------------ End Original Message ------------
Dear John,

If your interest in that equipment is for inspection of spot welds, I would recommend an ultrasonic test instead of weld resistance. Pl. contact me if you need more details.

Swamy
India



    
 
 
Richard Kazares
Richard Kazares
05:58 Dec-06-2004
Re: Electrical resistance measurements
Please note the comments of Phil Thayer - the M100A (current designation of product - with several generations of improvements) is available through Physical Acoustics Corp.

I mustm however take exception to Mr. Swamy's comments (below). While EVERY test method has its advantages and limitations, in the case of the M100A - it is currently being used by at least 2 MAJOR INTERNATIONAL auto manufacturers to inspect laser and laser-like (resistance and other methods) welds IN PRODUCTION!!

Both major manufacturers (that I know of) ran months (and in one case, YEARS) of testing the M100A methodology against other competing technologies and products - many cost as much as 200 TIMES the cost of the M100A. In every case the results of the M100A were as reliable as the competing methods.

Notice, I didn't necessarily say "BETTER" - simply that EACH METHOD has its share of "issues" - but that at the price point of the M100A, coupled with the simplicity, time to measure and ease of use - the M100A was the morecost effective solution, WITHOUT any lose (and in many cases - actual gains) in reliability and accuracy - compared to other methods.

PLease contact me directly via e-mail if you would like additonal information about the M100A product.

----------- Start Original Message -----------
: : : Does any one know where I can get hold of a piece of equipment called the 'AT&T Microhmeter'. This was produced 15 yrs ago for spot weld inspection (amongst other things). Unfortunately, the AT&T subsidary went into liquidation after a few years.
: : : I would assume it may be available second-hand, or that some company is still producing a similar device.
: : : Would be most interested to hear of what is happening in this field.
: : : regards
: : : John Turner
: : The subject ATT device was not effective at determining weld quality. It used a four point system where test current was injected into the surface and the voltage was measured with two probes. The resistance is not an effective method fordetermining welds in many materials due to several factors.
: : Materials will exhibit relatively good conductivity even when the fusion is not sufficient for a strong weld. Additionally, materials that are coated with zinc can be soldered together at the faying surface with zinc and exhibit good conductivity. They may also only be slightly bonded by diffusion. Resistance welds of this type will not survive even moderate impact and fatigue loads.
: : The risk you take is assuming a weld is good until it shows poor conductivity. In my opinion, you will only detect welds that are completely unacceptable while passing welds that are not fit for service grouped along with welds that are acceptable.
: : Our tests at a major automobile producer site did not show the resistance check method to be sufficiently robust for acceptance. If you are not going to test resistance spot welds then the device may be useful for other applications.
: : I am not aware of anyone still producing the resistivity weld checker commercially. You should be able to make one easily from commercially available equipment if you are handy designing and assembling electro-mechanical equipment. A suitable 100 A (max) power supply is available from RoMan Mfg. 861 47th St. SW, Grand Rapids, Mi 49509 Michigan, USA. The probe would have to be custom made.
: : The origginal unit was very portable. The power supply from RoMan will be rather large perhaps 15 kg.
: :
: :
: Dear John,
: If your interest in that equipment is for inspection of spot welds, I would recommend an ultrasonic test instead of weld resistance. Pl. contact me if you need more details.
: Swamy
: India
------------ End Original Message ------------




    
 
 
John O'Brien
Consultant, -
Chevron ETC , USA, Joined Jan 2000, 278

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
278
07:37 Dec-07-2004
Re: Electrical resistance measurements
John

as advised it is made by Physical Acoustics. There are units in the UK if you require a demonstration.Simply email me.


    
 
 
S.V.Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
07:40 Dec-07-2004
Re: Electrical resistance measurements
----------- Start Original Message -----------
: Please note the comments of Phil Thayer - the M100A (current designation of product - with several generations of improvements) is available through Physical Acoustics Corp.
: I mustm however take exception to Mr. Swamy's comments (below). While EVERY test method has its advantages and limitations, in the case of the M100A - it is currently being used by at least 2 MAJOR INTERNATIONAL auto manufacturers to inspect laser and laser-like (resistance and other methods) welds IN PRODUCTION!!
: Both major manufacturers (that I know of) ran months (and in one case, YEARS) of testing the M100A methodology against other competing technologies and products - many cost as much as 200 TIMES the cost of the M100A. In every case the results of the M100A were as reliable as the competing methods.
: Notice, I didn't necessarily say "BETTER" - simply that EACH METHOD has its share of "issues" - but that at the price point of the M100A, coupled with the simplicity, time to measure and ease of use - the M100A was the more cost effective solution, WITHOUT any lose (and in many cases - actual gains) in reliability and accuracy - compared to other methods.
: PLease contact me directly via e-mail if you would like additonal information about the M100A product.
: : : : Does any one know where I can get hold of a piece of equipment called the 'AT&T Microhmeter'. This was produced 15 yrs ago for spot weld inspection (amongst other things). Unfortunately, the AT&T subsidary went into liquidation after a few years.
: : : : I would assume it may be available second-hand, or that some company is still producing a similar device.
: : : : Would be most interested to hear of what is happening in this field.
: : : : regards
: : : : John Turner
: : : The subject ATT device was not effective at determining weld quality. It used a four point system where test current was injected into the surface and the voltage was measured with two probes. The resistance is not an effective method for determining welds in many materials due to several factors.
: : : Materials will exhibit relatively good conductivity even when the fusion is not sufficient for a strong weld. Additionally, materials that are coated with zinc can be soldered together at the faying surface with zinc and exhibit good conductivity. They may also only be slightly bonded by diffusion. Resistance welds of this type will not survive even moderate impact and fatigue loads.
: : : The risk you take is assuming a weld is good until it shows poor conductivity. In my opinion, you will only detect welds that are completely unacceptable while passing welds that are not fit for service grouped along with welds that are acceptable.
: : : Our tests at a major automobile producer site did not show the resistance check method to be sufficiently robust for acceptance. If you are not going to test resistance spot welds then the device may be useful for other applications.
: : : I am not aware of anyone still producing the resistivity weld checker commercially. You should be able to make one easily from commercially available equipment if you are handy designing and assembling electro-mechanical equipment. A suitable 100 A (max) power supply is available from RoMan Mfg. 861 47th St. SW, Grand Rapids, Mi 49509 Michigan, USA. The probe would have to be custom made.
: : : The origginal unit was very portable. The power supply from RoMan will be rather large perhaps 15 kg.
: : :
: : :
: : Dear John,
: : If your interest in that equipment is for inspection of spot welds, I would recommend an ultrasonic test instead of weld resistance. Pl. contact me if you need more details.
: : Swamy
: : India
------------ End Original Message ------------
Dear Richard,

Did I give an impression that ultrasonic test is superior to weld resistance measurement? I reread what I wrote but didn't understand it that way. I meant that if testing of spot welds is the area of interest, a simple ultrasonic test technique is available. And we used a very simple set-up. I have no commercial interest in any test method or equipment.

I will be happy to know more about the two applications that you mentioned.

Regards.

Swamy



    
 
 
Eng. Farid shawky
Eng. Farid shawky
00:26 May-31-2005
Re: Electrical resistance measurements
----------- Start Original Message -----------
: John
: as advised it is made by Physical Acoustics. There are units in the UK if you require a demonstration.Simply email me.
------------ End Original Message ------------
pls sent me thank you




    
 
 

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