Eddy current testing – 1

Hi everybody in these days we’re going to begin a new matter and in order to be on eddy-current testing so like what you do constantly we can first gain knowledge of concerning the general precept of this distinctive technique after which go on to see how it’s executed ok so allow us to and spot what is the common underlying principle behind this exact manner after which we will be able to see how it’s completed as a set okay so this is the topic that now we have at present in short sometime this is known as et which stands for Erika and checking out now coming back to this basic precept behind this so first let us comprehend what is meant via eddy current and why it is called eddy present okay now this name ad it comes from a flow pattern function you’ll discover in a flowing stream of liquid or gasoline when it encounters an quandary so this go with the flow direction across the main issue in a flowing move of liquid are referred to as eddies you would have obvious that in a flowing flow of water if the water the flowing water encounters any problem for instance like a stone like a rock it tries to head round it in a round path ok so this swirling of the water around this quandary is these are referred to as eddies ok now this eddy present is nothing however an caused present which we are going to talk about in more element so the path of this eddy present or this brought on current is similar to the path of the eddies which kind in a flowing move of liquid k so in view that of this as similarity this brought on current is called as Eddy present okay okay allow us to say you may have a conductor like this which is carrying an alternating current or altering present and in the event you carry a 2d conductor near to it so on the skin of the 2nd conductor you are going to have triggered present which will be having a drift sample like this as I said which resembles the eddies which type on a flowing stream of liquid around obstacles when the conditions are right k now if there is a defect on the surface this go with the flow pattern will likely be disturbed okay so on a completely defect free floor like this you’re going to have this type of flow in this detailed sample and there might be no disturbance on this glide path however now let’s consider there is a small discontinuity on the outside let’s say there is a discontinuity over here so when the in the present encounters this discontinuity the glide pattern round this will likely be these items like this so there might be a metamorphosis in this brought on current and therefore of that you would also see a transformation on this coil on account that the present within the coil is responsible for inducing this present k now if that you would be able to connect a detector to this coil which is able to realize this modification then this may tell you that there’s some discontinuity on the outside of the 2nd conductor and that’s how you will come to learn about defects and flaws on the surface of a conductor which is being brought almost this coil which is carrying an alternating current k so these eddy currents that you’ve they’re limited to the skin most effective and that is why this system is also a surface entity process ok however the question here is how do you discover that change on the grounds that this transformation due to the fact that of a small discontinuity will probably be very small ok so if you wish to detect that by means of a sensor connecting to this coil how do you do this and what parameter certainly you could possibly seem for to detect that change k so this is the question that we ought to answer to be able to have an understanding of the fundamental principle in the back of is method ok so let me provide an explanation for that to you as to how do you detect this alteration and what parameter is needed for that intent so when you speak about induction or electromagnetic induction you ought to go back to Faraday’s legislation which says that if a conductor contains a various or a changing current it is going to have a changing magnetic area round it and that altering magnetic area can result in a present or set off an EMF k either within the same conductor or to a 2d conductor which is just about the first conductor ok so this is often called Faraday’s law which says that this EMF which is the prompted EMF it can be a if we name that prompted EMF as VL this is because of the exchange in the magnetic flux which is created with the aid of the changing current ok so that you need a altering magnetic area to create this caused present or this caused EMF ok so this is referred to as Faraday’s regulation of induction k and this is the basis of the eddy present technique as i am going to explain now so in case you have n quantity of turns in a coil then this shall be n into D Phi DT where n is the number of turns okay but nonetheless the place we’re but to reply the query that we requested within the establishing as to what’s that parameter which is required for this to hook up with eddy current testing okay so for that apart from Faraday’s law we have got to take into account an additional regulation which is in regards to the course of the precipitated current okay so let us say on this circuit or on this conductor you’ve got a altering current flowing and considering that of that this altering magnetic area which is represented by using these arrows is created ok so with the intention to create that brought on EMF this magnetic flux has to change it has to both expand or scale down and as a consequence of that fluctuate you will have an brought on present but the query is how are you aware what will be the path of that brought about present k see so as to know that path of the precipitated current you have to take the support of another law which is known as Lenz’s legislation ok and it states that the course of the brought on current we’ll be such that it will oppose any change in the magnetic discipline which set off the present ok so the triggered present will oppose any change within the magnetic flux which induces the current k so that suggests when these alterations let’s assume the magnetic flux raises so due to this alteration there will likely be an caused present ok so that triggered present might be like this or it may be like this k so you do not know in which path it might go whether it’ll go clockwise or it is going to go counterclockwise so Lenz’s law will support you realise the path of the precipitated current based upon the conservation of energy ok so in the event you remember this course if this be the path of the caused present so this present will have its possess magnetic discipline and the path of that field may also be found via correct-hand thumb rule so if that is the thumb direction of the thumb of your proper hand then the fingers will point towards the magnetic field being generated by way of this current so if you happen to put your thumb around this you are going to see the magnetic field course might be like this k it’ll give a further colour to this so this will be the direction of the area if the course of the caused current is like this okay so that suggests this subject will probably be additive to this so this might be again add to this and the magnetic flux will further broaden which is against the conservation of vigor legislation k on the other hand if you bear in mind this direction k however by making use of correct hand thumb rule you’ll see the direction of the area on this case the course of the brought about magnetic discipline will be like this and this may increasingly then try to diminish this magnetic flux or this may occasionally attempt to oppose the expand in the magnetic flux and that is what the Lenz regulation say that the path would be such that it is going to oppose the change in the magnetic flux which triggered the present so on this case when it raises then the direction will be the direction of the present can be on this path k so now come back to the eddy present trying out so if this includes an AC present there might be an alternating magnetic subject also like this as a result of that alternating current so that they can induce this current on this conductor okay and if there are any discontinuities round this precipitated current there will be exchange within the induced present and therefore there will likely be some exchange on this coil which desires to be detected with the intention to realize the defect ok so let us see what is that parameter which is required to become aware of that and in order to do this we ought to go to the basics of drift of electrical current that implies we ought to go back to Ohm’s law we have got to from there and then eventually with the support of that we would see what’s that parameter which is priceless for detecting this change so Ohm’s legislation everyone knows if you are sending a present I by means of a register are then the voltage throughout it will be V equals to IR k so this is well identified the basic law of drift of electric current so the whole opposition or the whole resistance furnished to the drift of present on this case is the resistance R k however you might even have a an identical scenario but on this case the resistive detail is changed by an inductive detail so in that case the resistance to float of current would be the inductance which is denoted by L okay and allow us to call this present as IL to indicate that it’s flowing via an inductor k on this case in case of Ohm’s law should you plot the voltage or present then the voltage and the present are in segment k so allow us to say this is the voltage and this is the current there is no phase lag between the current and the voltage they’re absolutely in section however in case of an inductor if you happen to plot the identical then you’re going to see that there’s a lag between the voltage and the present which is flowing via the inductor ok so this is the primary change between a completely resistive circuit and a absolutely inductive circuit k in eddy-present testing what we use to induce the present is a coil k so the eddy present probe could have this coil within and it is a coil of a conductive wire so that means that coil may have each inductance and the resistance components ok so that implies we have to take into account a drawback the place in this present goes to glide go by way of a register and an inductor so that suggests you have got to don’t forget both inductive and resistive accessories okay however earlier than that permit me inform you right here what we be taught from the levels regulation is that this induced current is reverse to the exchange within the magnetic flux which prompted it and that introduces this bad signal within the Faraday’s legislation so this negative signal indicates that that the triggered present is hostile to the change of the magnetic flux which is that this okay so please keep in mind that we will be able to come again to it at the same time deriving that parameter what we’re looking for thus now coming back to this should you don’t forget a state of affairs like this the place both resistance and inductive components are there collectively in the same conductor then if you don’t forget the whole present ok then it would appear anything like this so let us say this is the present through the register so let us say this is IR then IL shall be this one so there is a segment lag between them and on this case the segment lag is ninety measure as you could see okay so that implies the whole present flowing by way of this particular circuit which contains both resistance as well as inductance factor shall be a sum of those two so that that suggests it’s going to be somewhere in between this like this so this whole present will name that as isay k so right here we have become introduced to a parameter Z which is referred to as impedance and this now represents the total resistance to the flow of current in a circuit like this the place you will have each resistance and inductance components k yeah so this impedance is the sum of each the resistance factor and the inductance aspect as we saw simply now so that suggests it will be a vector like this and this would be the phase angle between the resistance and the impedance okay so within the subsequent type i’ll exhibit you that headquartered upon this special parameter impedance we can assemble what is called as an impedance airplane and this is what is going to kind the basis for eddy present trying out ok so this may occasionally take some time so we will be able to take it up within the subsequent classification so in these days earlier than we shut let us take a moment to summarize so at present first we be trained about the eddy present and that is nothing however the induced current on a conductive surface when you deliver a present carrying conductor virtually a 2d conductive floor ok and the source for this eddy present as we mentioned today is a changing magnetic discipline which comes from a changing current or an alternating current k so that suggests when you have a conductor which is carrying an alternating or changing current it’s going to have a altering magnetic area additionally around it and while you carry this changing magnetic area of this conductor to the shut proximity of one more conductive surface then on the second conductor this eddy currents might be triggered and we also saw that these currents flow in a detailed sample like this which resembles the eddies which type in a flowing circulate of liquid when it encounters an main issue and that’s how this identify ADA current is given to this triggered currents okay and we also learnt that this comes from Faraday’s law which talks about electromagnetic induction or induction and the precipitated EMF if you name that as VL is the direct effect of this altering magnetic area D Phi DT there in Phi is the magnetic flux k then there’s a question as to what’s going to be the course of the induced present after which we saw that the answer to this query may also be located through using yet another law which is Linda’s legislation which states that the direction of the induced current might be such that it will oppose any change within the primary magnetic subject which brought about the current okay so that implies if the brought about EMF it is VL then we saw from Faraday’s regulation that it’s D Phi DT and this is antagonistic to the change in the foremost magnetic discipline so this may increasingly introduce a bad signal on this scale as a way to indicate that the induced present is reverse to the predominant magnetic field k and then subsequently we derived this parameter impedance which we will be able to call as lifeless from now onwards and that is the probably the most resistance and the inductance of the conductor in which the current is flowing ok for those who resolved it in phrases of inductance and the resistance components then as we noticed it’ll be a vector like this and that is the parameter that we are going to take up exceptionally within the subsequent class first we can derive an expression for this and then we will see how this specified parameter is used to do a degree in testing this what we’re going to absorb within the subsequent category so that is all i will have for in these days i will see you subsequent time and then we will speak about about the other points and we can continue from right here thank you

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