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Technical Discussions
nddung
NDT Inspector,
PHATECO, Vietnam, Joined Nov 2010, 16

nddung

NDT Inspector,
PHATECO,
Vietnam,
Joined Nov 2010
16
11:29 Dec-04-2019
Why two Gauss meter show to much difference value?

Dear All

Please advice me why I use two Gauss meter it show to much difference value on the same item. It is due to difference measuring area of each Gauss meter?

The photo of measurement please look at here https://photos.app.goo.gl/yLfBun14GcdUA72E6

 
 Reply 
 
Rick Lopez
R & D,
John Deere - Moline Technology Innovation Center, USA, Joined Jul 2011, 189

Rick Lopez

R & D,
John Deere - Moline Technology Innovation Center,
USA,
Joined Jul 2011
189
15:06 Dec-04-2019
Re: Why two Gauss meter show to much difference value?
In Reply to nddung at 11:29 Dec-04-2019 (Opening).

The black plastic unit is not a precision device and is not able to be calibrated/adjusted (many vendors sell these cheap/disposable items). The metal unit looks like one that may be calibrated, and the price tag happens to be quite a bit higher for the higher quality. Because the response of analog magnetic field indicators varies widely between manufacturers (although this unit looks to be made by a highly reputable one), the latest revisions of ASTM MT standards (e.g. E1444) have mandated multiple positive and negative field verification points in addition to a zero level. Does either device conform with this requirement?

 
 Reply 
 
Keith Brewer
NDT Inspector,
New Zealand, Joined Sep 2019, 6

Keith Brewer

NDT Inspector,
New Zealand,
Joined Sep 2019
6
23:26 Dec-04-2019
Re: Why two Gauss meter show to much difference value?
In Reply to nddung at 11:29 Dec-04-2019 (Opening).

Hi Ali

My experience tells me that these gaussmeters are good only for indicating polarity and excessive fields (degree of demagnetization) and useless for precision measurements.

Sensitivity is affected by exposure to high fields such as proximity to yokes and coils etc. Any original certification is unreliable from after the first use. I adopted the practice of general use of exposed meter with occasional verification using control meter kept away from magnetizing equipment. Excess field is indicated by less than full scale deflection, usually corresponding to one or two gauss indicated on the correct meter. This practice was adopted after failure by another contractor to achieve demag condition on a long drive shaft during field testing. I was unable to improve the result with my equipment and out of frustration I bought a new meter which confirmed over sensitization of the in use meter.

The MAC meter is by a well established and reputable US company and I have no doubt of its quality of manufacture.

 
 Reply 
 
nddung
NDT Inspector,
PHATECO, Vietnam, Joined Nov 2010, 16

nddung

NDT Inspector,
PHATECO,
Vietnam,
Joined Nov 2010
16
04:26 Dec-05-2019
Re: Why two Gauss meter show to much difference value?
In Reply to Keith Brewer at 23:26 Dec-04-2019 .

Thank you very much for your reply.

It is possible for the difference that is the size of Gauss meter? Each one measure difference size area so result is difference? If it is the size so there are any standard requirement for the structure of Gauss meter that it will show the same value even the difference size?

 
 Reply 
 
Manuel Haces
Director, - Wire rope inspection
Haces Inspección del Noreste and Wire Rope Inspection, Mexico, Joined Jun 2002, 124

Manuel Haces

Director, - Wire rope inspection
Haces Inspección del Noreste and Wire Rope Inspection,
Mexico,
Joined Jun 2002
124
13:54 Dec-05-2019
Re: Why two Gauss meter show to much difference value?
In Reply to Keith Brewer at 23:26 Dec-04-2019 .

Coulis you please provide Moreno info regarding thai MAC meter? Thank you

 
 Reply 
 

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