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- since 1996 -
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Technical Discussions
Rishi
USA, Joined Feb 2013, 2

Rishi

USA,
Joined Feb 2013
2
05:45 Feb-03-2013
About UT term Noise level

Hello All,
I am new in NDT. Just completed Level II. I am not understanding the term "Noise Level" which are used in many discussion in UT. What it is and how it happens in practical?

 
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Mario Talarico
NDT Inspector,
Italy, Joined May 2010, 411

Mario Talarico

NDT Inspector,
Italy,
Joined May 2010
411
23:54 Feb-03-2013
Re: About UT term Noise level
In Reply to Rishi at 05:45 Feb-03-2013 (Opening).

Rishi,
welcome to the forum.In general, the noise is a continuous signal can not be analyzed. In UT applications can observe it along the time base of the instrument during a control greatly increasing amplification (is called 'grass') or during control in materials with coarse structure.
In Eddy Current applications may depend of one or a combination of reasons: continuous drift in instrumentation, high wear in probe (coils short-circuited ), probe oscillation (lift-off), state of the surface in contact with the probe. In this last case is simulated on test-block with scratches diffuse (to delete it in the application).
In all cases the signals of defects are analyzed from a certain level (function of requirements) above this continuous unanalyzable signal (noise).
greetings
mario

 
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Debdutta Mallik
Consultant,
Malaysia, Joined Jun 2005, 37

Debdutta Mallik

Consultant,
Malaysia,
Joined Jun 2005
37
16:47 Feb-04-2013
Re: About UT term Noise level
In Reply to Rishi at 05:45 Feb-03-2013 (Opening).

Rishi,
Noise is a common phenomenon and can not be eliminated but can be minimized.
In a single sentence,noise is a result of several interferance and signal.
It is important to verify what is the signal to noise ratio before testing..Generally it is suggested to get at least 3:1 ratio,higher is better.
Debdutta Mallik

 
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Rishi
USA, Joined Feb 2013, 2

Rishi

USA,
Joined Feb 2013
2
14:10 Feb-05-2013
Re: About UT term Noise level
In Reply to Debdutta Mallik at 16:47 Feb-04-2013 .

Hello Mario & Talarico,
Thank you very much for your reply.
Noise level is mainly due to the geometry of the examination object surface or it is due to machine interference.

Regards,
Rishi

 
 Reply 
 
Mario Talarico
NDT Inspector,
Italy, Joined May 2010, 411

Mario Talarico

NDT Inspector,
Italy,
Joined May 2010
411
17:20 Feb-09-2013
Re: About UT term Noise level
In Reply to Rishi at 14:10 Feb-05-2013 .

Rishi,
Mario & Talarico ...... like Tom & Jerry, Simon & Garfunkel !
Talarico is my surname and Mario my name. Would be too beautiful be divided into two: one for work and one 'dolce far niente'. At the moment I work for two ...... My name is one of the most trivial and common italian names, so much so that in a piece of theater of Woody Allen father ends a series of recommendations to his daughter saying '.... and above all…. not marry someone called Mario ', an obvious allusion to immigrants, mafia, Italy. Finished digression, stop relax!
Electronic noise. Since each component produces noise each instrument is subject to electrical noise and distortion. The rules of characterization and verification of instruments and probes as european standards EN 12668/1/2/3 for UT and EN 13860-1/2/3 for ET regulate this matter. The / 3 is for test on equipment (equipment = probe + cable + instrument connected together) for the user, to perform periodic checks, which may include noise. This is procedure reduced to the essential: 1) maximize and put to 20% the hole 1.5 dn of V1 (sensitivity = dB reading). 2) Clean the probe and place it to the side 3) put the grass to 20% by increasing dB. The difference between the dB reading in 1 and 3 represents the signal to noise ratio of the equipment at that depth. The standard recommends this test at various depths (it is intuitive that this same test has a value signal-to-noise more unfavorable at depths much higher).
With regard to your observation , in the applications we encounter other sources of noise associated with the control and external to the equipment.
Noise due to the intrinsic characteristics of the material: in ET: local random variations in magnetic permeability during the control of ferrous materials (in the past I've always managed to avoid me this kind of control, very coarse until the advent of remote field); areas with the presence of ferritic phases in monel material : in UT: random signals due to the coarse structure.
Noise due to the surface condition of the components. In case of ET probe for internal the micro irregularities or pitting diffuse on the inner surface of pipe are an important source of noise, may generate a random signal of constant disturbance; detection with UT of a notche in cap weld , among signals of surface irregularities due multiple passes is often a task too hard function of state as weld and notche depth.
For other types of signals due to geometry or construction configuration that can interfere with the signal and involve changes in techniques and instrumentation (edges, veld cap and penetrations, misalignments in UT; intercalary baffles, increases or decreases in diameter, expandings in ET), I never heard use the term noise signal but rather baffle signal, denting signal, penetration signal and so on, being usually a single signal with well-defined origin.
And since should never complaining about because the worst is never at the end, in applications remain lurking other sources of noise due to the environment (network) or dysfunction of a part of the electronic chain.
At the moment I can not think of anything else but the list may increase.
Gretings
mario

 
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