we found or we concluded that we cannot have a very low value of D for buck nor we can have a very high value of D for boost and buck boost type of converters. So, therefore I cannot have a too low a voltage in a buck converter nor I can have a very high voltage in a boost or a buck boost converter maximum ratio could be of the order of 7 to 10 not more than that. Then that was the end of my lecture I derived a transfer function by using a transformer. What was the transfer function that I derived? I connected a switch battery to a transformer in this function in this manner I did not allow both the coils to carry current simultaneously purposely we connected this diode. Now, by doing that what we achieved whatever the energy that I stored here by when I close the switch gets transferred to the secondary. So, if I connect a capacitor here it gets charged. So, on a transfer function in this case happens to be N 2 by N 1 N naught is equal to N 2 by N 1 into V dc multiplied by D into 1 minus D. So, I have in addition to the transfer function of buck boost converter I have another term which is the terms ratio N 2 by N 1. So, there is a power supply what is known as the fly back converter this diode is also known as the freewheeling diode also known as the fly wheel diode. It is very popular up to up very popular up to say 150 and 200 is the upper limit why we will see. So, this is also known as the isolated buck boost because transfer function is same as the buck boost converter, but then there is an isolation between input and output. So, isolated buck boost converter I am not we already discuss the principle of operation it is same get connected diode accordingly and polarities of V naught this is positive dot this is also positive. So, this terminal very current enters the dot current enters the dot. So, this is positive ensure that only one coil is carrying current if of course, you can put a dot here at that time current leaves the dot. So, in this case also current should leave the dot I will repeat I have put a dot here and directly connected to the positive of the battery and when I close the switch current enters the dot no need I can connected in such a way that current can leave the dot as well. Now, if the current leaves the dot here current should leave the dot in the secondary as well. So, you connect the diode and the battery accordingly how to determine the voltage rating the diode and the switches is given here current enters the dot of the teller I too should leave the dot is explained it is fairly simple go back and read if you are if you are still doubts you can send me an email no issue and switches if an flux in the core must be continuous. So, I to flow in the secondary in such a way that direction of flux due to I 1 is same as that of the primary. Now, there was a question how does the current waveform look like in the primary there are two possible conduction continuous conduction and discontinuous conduction. Now, here conduction means flux in the core has not become 0 prior to closing the switch for the second time I will repeat continuous conduction in buck boost buck boost or chook converter is the inductor current here when I say continuous conduction implies that there is a flux in the core is finite prior to closing the switch that is all flux is continuous. So, the B H loop something looks something like this the flux becomes 0 this is the residual flux whatever it starts when I close the switch current increases therefore, the flux and when I open the switch current in the current in the coil in secondary decreases and therefore, the flux in the core as well and I close it again. Now, if the flux if there is a finite flux. So, B H loop looks something like this which mode we operate we will discuss. So, if I operate in continuous conduction in other words there is finite flux or in other words when I just prior to closing the switch for the second time in the primary there was some current flowing in the secondary there was some current flowing in the secondary. Instead the moment I close the switch whatever the current that was flowing in the secondary get transferred to the primary now it is I 1 increases linearly it reaches a peak I p. Now, the moment I open the switch here this I p gets transferred to the secondary now I need to take care of the turns ratio I p is flowing in N 1 what should be it is equivalent when it is flowing in N 2. So, and current decreases similarly this is the value of current just prior to closing the switch it is flowing in N 2 turns. When I close the switch for the second time it gets transferred to the primary and it starts flowing in I 1. So, this value you need to you can determine by knowing the turns ratio and see here current in the coil I 1 increases flux also increases it starts with the finite value of flux because flux is continuous here it was flux current in the secondary was carrying some current there was some flux here it increases and therefore, decreases generally operated in discontinuous mode. In other words secondary current has become 0 therefore, the flux in the core there is some time neither the switch nor the diode are conducting after sometimes switch S is closed and current starts increasing from 0 and this is the B H loop if it is continuous if it looks something like this. Now, why am I saying that generally it is operated in discontinuous mode reason may be bit reason is quite obvious if I operate in this mode and accidentally say for example, load has changed see that load has changed output therefore, output voltage will fall the signal comes to the controller saying that output voltage is falling. So, naturally the controller will try to increase the value of D duty cycle and if there is no limit on D and if D increases. So, high value your core may get saturated core may get saturated see I will repeat I just show you the you want generally the output voltage has to be regulated V naught ref this is V naught actual now, load there is a sudden increase in load therefore, nothing has happened to the primary primary does not know the controller does not know the load has changed current capacitor starts supplying the power capacitor voltage will try to fall. So, V naught starts decreasing it is trying to fall it was almost constant now starts decreasing. So, this is error increases there is a regulator assuming that there is no limiter assuming that there is no limiter D has to in D will increase controller says increase D by increasing D I can supply more power. So, increase D now this increase in D might result in core saturation. So, might increase in D implies that switch is switch is closed for a longer time. So, flux continues to increase it I have shown you linear increase because core is not saturated now for a higher value since the D has increased it may so happen that core may get saturated and if that happens you can see may be smoke coming out of the fly back converter because if the transformer core is saturated current will be limited by the internal resistance of the coil fortunately here solar panel there is a inner and short circuit limit. So, you may have to take care so that nothing should happen to the devices transformer as well as other components if you operate the core in saturation. So, generally thumb rule is thumb rule is we operate in discontinuous core mass saturate this how we have derived transfer function increase in flux should be equal to decrease in flux that is for steady state condition same transfer function we have derived. Therefore, magnitude of it is can be significantly different D max is generally kept at 0.5 and choose N 2 by N 1 suitably now which is a very important parameter it is L 1 is a very important parameter that should answer why we are why this circuit topology is popular for low power low power why it is not suitable for high power that should answer the question now what are we doing when I close in the switch the energy is storing energy is being stored in the primary inductance L 1. So, current is the peak value of the current is given by V dc divided by L 1 into D into t provided it is operating in discontinuous mode current is starting from 0 increases linearly it is a peak value of I p is given by this this is the peak value what is the total power of this converter in the sense the p in given by V dc is the input voltage I am assuming it to be constant average of this because from d t to t current is 0 source does not supply any power from d t to t. So, average of this is area of the strangle is half I p into d by d. So, power N input power is given by the input voltage V dc into the average value of this. So, that also should be equal to power out neglecting the losses. So, neglecting the losses this is the expression for I p d is limited to 0.5 now you see what will happen to I p as the power rating increases. So, as I p increases primary inductance for a given value of d will decrease. So, your overall size of the transom are of the converter size may increase because of the peak currents. One of the advantages is output can be significantly output voltage sorry not output power output voltage can be significantly different other is isolation third is I can have multiple outputs of course, when you are doing solar this may not be very important. What I mean is I can have multiple inputs I can have multiple inputs current enters the dot current enters the dot current enters the dot current enters the dot. So, one primary large number of secondary of different voltage ratios of course, regulating this voltage is may be difficult of course, but then there are solutions. So, this will having N 2, N 3, N 4. So, I can have different voltages large number of voltages it may not be possible to have using the conventional buck boost or a boost converter. So, there is another advantages of having using a transformer, but then with large number of multiple winding. Now, one of one way to see here I said the transformer may get saturated how do I take care of the saturation I can take care of saturation by providing a small air gap because if there is an air gap it will be difficult to be difficult to saturate, but then the moment I use an air gap there is going to be a leakage coils are not tightly coupled. Now, if there is a leakage what will happen when I open the switch see here see if there is a leakage and the transformer equivalent circuit now become something like this. I am neglecting the winding resistance this is V naught, this is diode, this is L m, this is L s L. When I close the switch this is the way of the direction of current and when I open the switch switch could be anywhere I will open the switch whatever the current that was flowing through L m will flow through diode and V naught what will happen to the energy associated with this inductor. There are solutions of course we have to handle now we have to try to address or we have to address the energy associated with this inductor. My circuit overall complexity increases. So, here is one such solution. So, you close S this is how the circuit current will flow open S inductor current was flowing through this that leakage inductance. This direction of current should remain the same for the leakage inductor and it has to flow back to the source. So, what I will do I will modify the circuit something like this close the switch. So, it will flow magnetizing current increases open S now this diode leakage battery. So, that is the reason see in order to take care of saturation I provide an air gap if there is a provide an air gap leakage flux will come if there is a leakage flux my circuit complexity will increase that is what you try to address one problem it will give rise to another problem, but then solution do exist. So, these are the various possible configuration only the diode you need to take care of the diode connections you should not allow the both the cause to carry current there in the fly back converter is the time. Now, I will take few questions please come in chat mode. So, there is a question sir we know that example voltage source is a battery please tell me practically a current source yeah current source if I I do not how do I how do I construct a current source see something like this by regulating this voltage say I have a fixed voltage V dc this is L by regulating this voltage can I can I make current flowing through the inductor approximately constant something like this. See if this if V 2 if V 2 is less than V dc current increases say slowly current increases if V 2 is greater than V dc current decreases I will redraw here I will repeat if V 2 is less than V dc current flowing through the inductor increases I assume that some steady state has reached current increases the moment it touches an upper limit I will try to reduce this I will try to increase this voltage. So, if this voltage is in higher than V dc voltage across inductor is now negative current will fall when it touches a lower limit I will again decrease this voltage V 2 V dc I am not going to do anything the next question is can we have fly back converter having multiple output from different DC sources. So, it should be multiple input can we have fly back converters having multiple input from different DC sources it should not be multiple output I have type. You mean to say that you have multiple inputs from different energy sources for fly back converter. No, no, no see what you do is you have n number of sources coming n number of sources coming to one common DC link n number of sources coming to one common DC link are you with me and then and a fly back you can have n number of sources coming solar 1 solar 2 solar 3 may be a small windmill rectified whatever and you have you can have this, but then remember this is suitable for low power not more than say 100 to 150 watts in principle yes you can have one common DC link connect all the sources there why it is not it is possible this is what you have in mind, but can we have fly back converter having multiple inputs. See let me not can you can you draw the figure what you have in mind scan it and send then may be tomorrow I will try to answer multiple input fly back input I do not know see this is what you mean these are the various inputs and may be I have a selector switch connecting to various this one multiple inputs means what in the sense I have finally I have to connect this transformer to I have to finally I have to connect a transformer to a source. In the transformer there will be multiple primary coils. Multiple primary coils let me not answer straight away in the sense now this question is multiple primary coils and one core no no one transformer no no let me not let me not answer this I have to study that I have to see what will happen to the flux in the core because you are trying to energize the switches they may not be there is no are they synchronized all the switches. So, no no what I am saying is you are saying may be then I think I need to need it you have to see what exactly is happening in the flux in the core let me not answer let me think the question is how to find d max so that converter will not you know the question of converter saturating is a transformer saturating the question is how to find d max so that converter will not such converter does not saturate is a transformer saturating because you are the one who are designing the transformer you are the one who are designing that inductor you should ensure that after all it is b h loop will tell you whether it is saturates or not your n i photon should not increase beyond the saturation this is h this is b h is h is proportional to current that is flowing when the close when the close the switch. So, you should ensure that you should not go the saturation level the question is if v d c is varying continuously how can we regulate v naught see fine is a good question v d c is varying continuously what are the what are the input what are the minimum and maximum limits of v d c variation and d is generally at point five. So, you choose choose for a minimum condition for minimum input d is point five now choose n 2 by n 1 accordingly now as v d c increases v naught is the same now d has to come down it is transform may not get saturated if follow what I am saying v d c now you have to you cannot be just saying that v d c is varying continuously fine what are the upper v u and v l.  So, therefore as v increases same v naught d has to come down choose n 2 by n 1 for v l and point five as v l increases above sorry as v increases above v l d has to come down very fine you are not increasing d above point five. So, the apprehension of transformer getting saturated is not there what is the maximum reverse blocking voltage rating there is d c voltage here it has to block d c it is please try to under what is the reverse blocking question is wrong in a sense there is no reverse voltage being applied across the switch here that can happen only in a c and if you have if I am using an a c then I need to choose the devices accordingly conventional BJT, MOS, IGBT they will not block the reverse voltages. So, as I understand correctly it looks like your question is what is the voltage rating of the switch see when the switch is open when the switch is open what is the voltage it has to withstand this is v d c plus the voltage induced here that is v naught into the turns ratio now turns ratio take suitable definition v naught is being applied to n 2 what is the voltage induced in n 1 this is with. So, this is positive or equivalent circuit v d c assume the dot is here dots are negative both the dots and this is the switch s this is the ground there is no reverse voltage being applied across s. So, voltage rating is v d c plus the induced voltage in the in the primary winding that is v naught into turns ratio turns ratio now you choose your be careful while substituting the value of n it is v naught is being applied to the secondary having n 2 turns what is the voltage being induced in the primary you need to find out and that is n here. The next question is why cannot we use boost converter alone to step up the voltage from 24 to 230 you want to use only boost converter please go ahead and do my best wishes to you. Next question why fly back converter is not popular for power rating about 200 I showed you the transparency as well this is the expression for p in is equal to p out now you have to do your paper and you have to take a paper and a pencil and design and you have to find out what will happen to the transformer as the power rating increases what will happen to I p the p currents size. So, I encourage you to do a simple transformer design problem say for example, 300 watt transformer only one winding carrying current at a time fix some input d is 0.5 calculate I p calculate l 1 and try to get this l 1 what will happen to the size and the p current I p. So, can we know the power rating of buck boost and buck boost converters for design application see we discussed about this converters I told you we have a problem when if I if there is a large ratios of input and output that is all power rating we have not discussed we can power rating is not a problem only is the voltage ratings if the output voltage ratio of v naught by v d c is very high then I may not be able to use the conventional boost or buck boost it is a problem with the voltage ratios.


Hi everyone, Joe from jaskiescasebreaks.com coming at you with a box of origins football and international blaster break number 11. The last fellow, the only filler we had to do to unlock that choice division break coming up in the next video. Let's do the break first. Big thanks to this group for making it happen. All 32 teams are in. Let's roll it. Let's randomize it. Five into two, seven times for names and teams, different dice for the giveaway part two. Three, four, five, six, and seventh and final time. No trade windows in these either. Let's just blast through this blaster. Two, three, four, five, six, and seven. Oh, the filler says three. Come on, Joe. Yeah, it should be four. It's for four. Three are we obviously did already. Hold on. Stand by filler. Stand by filler people. It's for four. Obviously, three already did. But now it's official. All right. Back to this. All right. There's the first half of the list right there. Second half of the list right over here. I was just making sure that Thomas and Jayce, I was just making sure you guys were paying attention. You guys passed the test. Congrats. NFL playoffs coming up this weekend. That should be really exciting. Looking forward to that as the final printout hot off the presses. Who's going to win the NFL MVP? According to this random website here, tracking NFL MVP odds, Mahomes looks like the prohibitive favorite at minus 1,600, Joe Burrow plus 900, Josh Allen 15 to 1, Jalen Hearns 15 to 1. Well, Raymond, this is just a filler box. You're not. This is really, you're chasing the division spots. The break itself doesn't. Not as consequential. Hey, if those two, if those two teams gets you a spot in the division break, then you'll be happy. All right. Now let's flip back to this list here. The whole point of this obviously being who's going to win those division spots. So $18 and 99 cents could help you win $125 spot. It should be pretty nice. All right. Big thanks to this group once again. Just the top four after three fingers crossed. Good luck, everybody. One, two, and three. So there's three times top four. Get those division spots and you'll be in the next video. Spot five, sorry, Carter got close there, but no cigar five through 32. Thank you for giving this a shot. Appreciate it. Top four, you're happy because you're in the next break. Corey, you're happy. So is Brian, Russell, and hey, there you go, Raymond. Brown's and Lyon's not too bad, right? Because you got yourself a spot in the next break. Jaspy's casebreaks.com. I'm Joe. I'll see you in the next video.


Hi everyone, Joe for jazzy's casebreaks.com coming at you with 2022 tops chrome baseball update edition one box ram team Break number four our last filler last one got to do to unlock that that hip-raid baseball break That's coming up in the next video, but first the break itself big. Thanks to this group for making it happen All 30 teams are in let's roll it. Let's randomize it three and a five eight times for names and teams one two three Four five six Seven and eight we got Eugene down to Steve We'll do a different dice will for the giveaway part at the end three and a five eight times for the teams one two three four five six Seven and eighth and final time After eight we got the rays down to the jays. All right, so there's the first half of the list right over here And the second half right over there no trade windows And let's print and rip There it is doing a whole box. I am a whole box Final printout hot off the presses. I think we have a don't we have a case of this loaded up on the site somewhere Yeah, we've got a full case of this a random division break That is part of the promo two full division spots left plus a couple fillers You want to get in on that? the the filler for the Donner's Optic baseball Do the tool dual case rate the double header is sold out and now we just need someone to grab one full spot And we can lock that in on the schedule Which is good with plenty of time to spare which means we'll have time to squeeze in some more breaks at the After that break all right is a is TCU and Georgia like playing their Their seniors yet like the seniors who usually don't get snaps like Some fourth string tight end who's gonna go to med school after this or something like that Give that kid a snap or two Throw him a pass. There's a nice wander Franco Julio nice Julio Rodriguez Kevin and the Mariners Oh That's who scored the last TD the backups. I Was telling my colleague Chris all guys. I'll I'll stake you TCU plus 50 Will you take it? He said no. I'll be with juniors to you virtue in the Royals. Oh There the all star game refractors are not numbered the Non-alts the regular cards are Refractors are numbered Purple cards are exclusive to this set not numbered though. They will ship. There you have it. All right now important part about this is who is going to Win those hit parades spots That's the whole point of this so second and final dice roll Six and a four ten times top ten after ten gets into the next break hit parade Coming up in the next video one Two three four five six seven eight nine and good luck 10th and final time So from 11 on down Craig sorry Got very close Just short But I appreciate you and everyone trying 11 30. Thank you Top 10 happy times for you. You're in the next video Steve Birch is happy So is Bartholomew Jason Steve Steve Steve Steve Steve Eugene and Steve Steve did have a lot of spots There you go Congrats to the top ten after ten. We'll see in the next video. Jasper's case rakes calm


Hi, it's Bridget. Welcome to Above Life Channel. The purpose here is to inspire your spirit and to fill you with hope. Today we're going to have a conversation about control. It's so funny. I literally hear in my head the Janet Jackson song, control. Okay, so some of you that might be like not in your wheelhouse. So take a minute to Google it up or look it up on YouTube and say control. Energy of control is something that I think our mind really buys into and really thinks is just this great, wonderful thing. And the truth is it doesn't really exist.  It's not even real. There's this false narrative around the idea of control, which is to create this presence of what we perceive to be. Safety, security, a structure that gives us a understanding of how to act, how to be, what to expect. And really control is something that isn't even possible in our human form. And I don't know if it's possible in our spiritual form, because I haven't been just pure spirit without a body. I can tell you though that part of our human mind experience wants to, our human mind really wants to help contain and understand what's happening in our human experience and it uses a concept or idea of control in order to help do that. So control isn't a bad thing, not at all. But it really is getting at our root core desire to feel secure, to feel safe and to have known, to know things. And again, this kind of leads into the idea or the concept of the unknown, which is really upsetting, which is really off-putting as we've seen with the pandemic experience. The unknown creates so much fear and so much anxiety and gives this ambiguity space that provides the opportunity for so many different stories and so many different spins on things that we don't know what's fact and what's fiction and some people don't even care about the difference between the two. It's more about the feelings, not fact or fiction, but it's about feeling, feelings, which is why the amplification of being an empath or being a hard intuitive has become so much a priority and so very important and acknowledged and recognizable to so many people at this time. So how does an empath deal with control? Are you or do you find yourself being a control freak? Ooh, ooh, ooh, ooh, ooh. Is that a hotspot? Control freak? The need for control is really this desire for an assemblance of order in order to be able to process or understand things that are happening and also to provide a level of security. We've established that safety and security. However, it doesn't exist. So if control actually doesn't exist or it's this unattainable thing, then where does that leave us? How can we be comfortable? How can we be safe? How can we know for sure? Well, you can't. There's no such thing as control. It's an illusion. And you can't ever be 100% sure of anything because there is always room for change, for shift, for things like free will, for things like the unexpected, for newer opportunities to bubble up, for you to become more aware of something that you haven't been aware of before, a new level of thinking, a new or deeper, broader understanding, which creates different opportunities, which promotes change, which is not anything related to control. Change is not controlled. It's not even close. Change is more of an art. And it's a constant fluid part of life, like breath, like air, like being. The energy of control is quite a bit like certainty. And I know that for myself, I want to be certain. I want to know for sure. I want to be present and able to process and understand the life that is happening around me. I want to be able to engage and be part of fully this life that we're gifted. And I know that I have to release control in order to do that. In addition, the concepts that we create in order to establish a false sense of security or reality isn't to be judged, isn't to be compared. It is simply to be acknowledged and to know there is no way to know for sure. So the idea of control is a myth. It sets you up for disappointment, for misunderstanding. So let's try to shift this, our relationship with our needs for certainty. And to not misunderstand that safety can't exist only unless there is certainty. That's not true. You can be safe and have a fluid life experience and allow for change to happen. And you can be safe during times of change. Certainty, if you can allow yourself to be loose and flexible with what that actually means, it doesn't have to be tied to an outcome. It can simply be part of your process, part of the bigger picture, the grand plan, the incredible experience that you're on this journey, the adventure of life. So let us take a moment here to breathe and be with an understanding. Let's deepen our understanding of the energy of control. This is not something that we can rely on. We can't depend on control. We can't depend on the old ways of thinking and doing. We cannot look to a false sense of security because now is the time as an empath for you to step into a broader, greater, more connected and a whole understanding of how the world works, soul to soul, energy being to energy being, to see one another with the power and the freedom and the flexibility that we can only have when we are sovereign, when we are able to make clear choices, when we are amplified in our oneness and yet brought together by solidarity. None of these things can occur when there is this constant strive for control or this need for control. It does not exist. It cannot coexist in a place where the spirit longs to be free, not free from the body or the mind, but free, free to do and express and to feel, to connect with your heart and your mind and your body. The soul desires freedom and expression. The soul craves for the spontaneity and the moments of opportunity that come when there is not containment, confinement and restriction. These are byproducts of control. Misunderstood, yet still, elements that do not support your spiritual growth and your personal development.  It is an old story that does not help you expand and grow and reach your limitless potential, but it holds you back. And not just to you, but everyone else that buys into the structure, the need for this secure, restricted life where in control is the goal and it is also the process or the way. Control is temporary. It is short-term. It is not withstanding. It has no longevity. It cannot bring you to the promised land that you desire. It cannot gift you your dreams, your hopes and your wishes. For those are manifestations that come only when the soul can be free to express, to experience, to live life. Now, I do not know what to tell you as far as advice about how to get there, how to do that, how to achieve that freedom that the soul desires and yearns for and longs for and needs so deeply needs for its fulfillment of life on purpose. I don't know how to tell you how to do it because you are unique.  And as such, you have your own unique formulas, different dreams and hopes that are strung together to create your life, vision, purpose and mission. But it's not about knowing how to get there. It's about knowing that there is a worthwhile, worthy purpose. And it's not about restriction, containment or confinement like control. It's about freedom and expression and expansion. And it is real. It is very, very real. And I know it's in your heart. Touch your heart right now. Just put your hand on your heart and take a breath in. Head and exhale out. And rest in the knowing. But in your heart, you are truly free with the wisdom of your soul to light your way, softening the energy of the mind to invite it in, to include it in the freedom of expression of creativity and imagination and hope for the future. Hold a higher vision. Expand your thinking. Open your mind and be here and present for the now. Nice breath in. Big exhale out. Yes. And I hope that your spirit feels inspired today as you listen and filled with hope, the light of hope and remember, this is your life after all and you get to live it. Just live it. This is Bridget. Thanks for being here. On this Sunday morning coffee podcast episode, if you're looking for me trying to connect, find me on social media. I had Bridget inspired on Instagram, Bridget inspired on Facebook, above life channel on Facebook and on my YouTube channels, above life channel and the fairy grasshopper that is fairy grasshopper on YouTube.


6. Effects of stress. Insomnia. Insomnia is when you cannot sleep. Insomnia is an effect of stress. Worrying about school, work, or family can sometimes cause insomnia. 7. Angry. Anger is the emotion or strong feeling you get when someone does something bad to you. When someone has a lot of stress, they tend to get angry easily. 8. Sleep. Sleep is to rest your mind and body, usually at night, when you are lying in bed with your eyes closed. It can be difficult to sleep when you feel stressed. 9. Cry. To cry is to produce tears from your eyes, usually because you are unhappy or hurt. Yelling at someone or saying mean things might make them cry. 10. Panic. Panic is a sudden, strong feeling of fear or nervousness that makes you unable to think clearly. Don't panic if you make a mistake on your homework. 11. Headache.  Not getting enough sleep, eating unhealthy food, and too much stress can cause a headache. 12. Stomachache.  When some people experience stress, they get a stomachache. 13. Depression. Depression is a medical condition that makes you very unhappy and anxious, and often prevents you from living a normal life. Exercise can help prevent depression. 14. Sick. To be sick is to not feel well physically, like to have a cold or the flu, or other physical problems. If you are sick, you should stay home from school or work. Sad. To be sad is to have a feeling of unhappiness. It is common to feel sad when you feel a lot of stress, and there are many problems in your life. The end.


Welcome to All Hands Update, I'm Petty Officer Ian Cotter. The 2014 tax statement schedule has been released on the MyPay website. Reserve sailors can expect their W-2 to be available January 7th. Active and Reserve Marines will receive their W-2 January 14th, while Active Duty Sailors will receive their W-2 January 24th. Tax season can be a stressful and confusing time, so take advantage of programs that are designed to help you. Active Duty Sailors, their dependents and retirees can use the Volunteer Income Tax Assistance or VITA program to get free help with filing their taxes. To find a local VITA site near you or to find out how to be a volunteer, visit the IRS website. If you contributed to a Roth TSP this year and wish to continue into 2015, you must submit a new Roth TSP election. You can do this on MyPay or submit an election form to your finance office by January 31st. For more information, visit the MyPay website at mypay.dfast.mil


This is another lecture on non-destructive evaluation or testing of structures or machine components for fault detection and in this module we will be discussing on two techniques today in this class. One is on acoustic emission other being the eddy current testing, first I will discuss about acoustic emission. So, as the slide says you know all materials essentially if they are stressed they will give back some energy and this energy if it can be captured and analyzed it gives us clue as to what is the defect in this material. So, if I look at this definition or what this acoustic emission is, so if any body or elastic body is subjected to any kind of a stress it is going to release an acoustical energy and this energy is called as an acoustic emission event as if the material or the machine is crying because of a stress or load on it. And the peculiarity or the characteristics of this energy which is known as the acoustic emission is that it is an body is stressed whether you can be pulling it with some force. So, this gives out some sort of an energy in all directions and if this energy can be sensed by a transducer this gives a clue as to what is the defect or the condition. If there is no defect the amount of energy will be different if there is a defect this amount of energy will be defect. There are certain characteristics of this acoustic emission signal first of all it is in the megahertz range and then this is either in the form of continuous wave form or as in burst of certain energy. Now, the acoustic emission condition or the strategy is to have this transducer we should be able to detect this kind of stress waves and this is what we are going to look into this in this course and how it can be measured analyzed and so on. So, if I was to look into the applications of acoustic emission it is an non-destructive testing of heavily mechanically stressed components or complete structures of fiber and first plastics or composites as used in the aerospace industry. So, this can be used both for materials which are metallic and non-metallic. Acoustic emission can be used in materials research to understand the material properties and breakdown of the failure mechanisms of the damage behaviors and materials. Acoustic emission particularly in non-destructive testing or condition based maintenance is towards inspection quality assurance example monitoring of welding and wood drying processes, series inspection of ceramic components, scratch test and few more. This is used to detect leaks in large reservoirs or large containers it is used for seismic research and so on. This is one photograph of an acoustic emission testing been done on 25 meter length pressure vessel of diameter 4 meter this can be instrumented with pressure sensors or acoustic emission sensors and this signals can be analyzed to find out the source of the leaks. Like this example or this diagram shows I can be having many sensors around the location and each of the sensors will give us an acoustic emission signal. So, by the method of triangulation the source of defect can be identified ok, but as I was mentioning you these signals could be their time domain they are very high frequency time domain they could be continuous signals A signals or they could be in burst burst or continuous signals. Now, there is a little historical development in this acoustic emission systems because they are of the order of few megahertz ok. Now, to do any signal analysis if you will recall the class on computer aided data acquisition to do signal analysis on such high frequency signal. We always have to if you have to do DSP on the signal we have to acquire them through an AD process and then we can this is the acoustic emission signal we have to an AD process then once we have the digital data these are the digital data we can do some sort of an analysis on the computer. However, when DSP was not developed in the early days people used analog signal analysis processors and in particular because they are high frequency signals all we could do was at most find out the RMS level or the peak level or may be the time duration etcetera or the number of peaks in a given time. So, these were very gross parameters which were used in and I will show the details of these parameters this is how they were being done. So, basically it was a E transducer and then some sort of a signal conditional and then we have the display signal conditional and A E transducer ok, but this kind of instrumentation was good enough to detect no defect and defect and it gave us a qualitative feel of the defects in a component or machine and this is how a typical transient acoustic emission signal looks like mind you this is in microseconds. So, you can understand it is a very very high frequency signal and this has to be captured in a device you know this is an analog device ok from on which this has been captured like a digital storage oscilloscope ok and from this time domain signal certain features could be found out like number of peaks beyond a certain threshold, number of peaks occurring in a time period. So, all this could be done through a simple analog processor and as opposed to the transient signal which was mostly a burst this is what is known as the continuous signal there is some sort of an energy signal either this is in some millivolt we get in a particular time waveform of the continuous A E signal. There is another related effect in acoustic emission which is known as the Kaiser effect. Now, this is because of the fact that it was named after Dr. Kaiser which says that as an irreversible phenomena in the behaviors of material called the Kaiser effect and this says that this is the effect of the that act indicates that irreversible processes during plastic deformation in the strain which can be shown by using a visual lateral crystal and because of the Kaiser effect whenever the material has stressed beyond the earlier limit then only we will have a meaningful acoustic emission signal coming out of the system. For example, just to illustrate the Kaiser effect suppose I have a machine it has been stressed and there is a defect. So, I am getting some signal some acoustic emission signal. Now, in the next instance if it is stressed less than this whatever is the acoustic emission sensor signal it will not be realized till I come to a new level of stress which is higher than the previous signal and then only I am getting a high signal. So, this is essentially known as the Kaiser effect. So, if I was to look into the analog A E process chain. So, the machine or member is stressed and because of this there will be release of the elastic energy this wave will propagate and then this acoustic emission signal will be detected and then you can record them with number of sensors and then put them in a personal computer to analyze the signals. So, test object in application of load which produces the mechanical tensions, source mechanisms are basically they releasing the acoustical energy or the elastic energy wave propagation from the source of the defect to the sensors. Sensors basically convert the mechanical wave into an electrical signal. So, acquisition the converting the A E signal into electronic data set and you can either display it or store the data. So, in the modern methods of acoustic emission sensing there has been an A to D converter which had explained for mentioned few slides ago. This A to D converter are nowadays available. Say for example, if I have to sample an A E signal which is around 2 megahertz at least because of the Shannon's sampling theorem my sampling frequency f s should be greater than at least twice f max. So, at least greater than 4 megahertz in this case. In early days getting A D systems with such high sampling rates were a problem. So, acoustic emission was one way the digital signal processing for acoustic emissions was not very popular, but off late A to D systems with high sampling rates are available and they have been used in acoustic emission signal analysis. So, this is typically like I mentioned to you on the other class regarding ultrasonic transducer where I had a piezoelectric element which was made to resonate. Similarly, we have an acoustic emission sensor where in piezoelectric crystal is there and then this will be giving it will be sensitive to this surface the waves which are coming through the structure to the surface and then we will get a signal corresponding to the stress waves. And again because these are all capacitance and we are very careful regarding the noise and that is one of the important issues practical issues of AE is the noise or poor signal to noise ratio. Off late acoustic emission has mostly been used for a quite quick qualitative estimate estimate and location of the signal source of defect rather than unlike vibration where in we have cases like the signal I can be very sensitive I mean other I can say 1.2 meters per second square or 1.209 meters per second square they are two different quantities and this can be sensed by systems which is not true in the case of acoustic emission because of this capacitance and then we have to be very careful about this cables not be band strained and then this special cables which reduces the triboelectric noise are to be used in acoustic emission systems. And again this AE preamplifier has a low input noise to distinguish smaller sensor signals from electronic noise. It has a large dynamic range to process high amplitudes without saturation, large range of operating temperature for applications in neighborhood of low temperature vessels as well as above the transition temperature from brittle to ductile material. Usually a supply voltage of 28 volt for the preamplifier is given through a signal cable and then for the calibration pulse and all that will be required. Filter sets depending on the acoustic emission particularly for leakage and corrosion test the filters are within anywhere from 20 to 100 kilohertz. For metallic component testings we have filters from 100 to 300 kilohertz and above 300 kilohertz for small distance between the sensors. Certain terms which are used in acoustic emission I thought I should be mentioning it to you here in the class. So acoustic emission is a transient electric sorry elastic wave produced by the release of elastic energy during certain processes which could be mechanical stress. Event is this burst or if you see source of the origin signal is the signal which you get from the AE transistor. Signals could be a transient or a continuous burst. AE activities occurrence of an AE signal, AE intensity is the strength, AE channel is the number of such measurement sensors which we have and usually we require a multi channel system in machine structure so that by the method of triangulation we can find out the source of the acoustic emission. So some in the time domain we can set lot of triggering events for example this is the negative threshold with the positive threshold. So any number the number of peaks beyond a positive threshold can be used to quantify some of the AE signals like above a particular threshold and the first time the crossing has happened before the bureau arrival time. So all these kind of signals can be processed then the maximum amplitude number of overruns signal saturation so there are lot of features which have to be measured and monitored in such acoustic emission signals. So arrival time is the absolute time of first thresholding crossing peak amplitude, rise time, time between the first threshold and peak amplitude signal the recent time interval between first and last threshold crossing. Number of threshold crossings are the AE counts in one direction. So AE counts were earlier used as a method of detecting whether an acoustic event has happened or not. AE count increase in AE count represents a defect in the structure. So this AE can be calibrated by what is known as a pencil lead break test and this is one example where in you see how the principle of location is used. Sensors 1, 2, 3, 4 around a defect and you can see if the signal from the source defect is one depending on the time delay for the signal to come to one of these sensor locations people can have a 3 dimensional software I mean graphic software wherein they can triangulate around 4 spheres or maybe they use 3 spheres to triangulate wherever the 3 spheres meet will be if I can draw them in a 2 dimensional plane suppose one event is here you can draw a circle around it, circle around it and circle around it. So wherever these 3 spheres meet that will be the location of the defect from each of these sensors. So this kind of triangulation algorithms are there and this is just one such locations from a software which are used. So AE transducer by having multiple AE transducers and doing a triangulation the AE source can be determined. Though AE has been very qualitatively popular for knowing whether a defect has occurred and not occurred because as I was telling right in the beginning the material cries under stress and this cry signals are high frequency signals which has to be captured by piezoelectric crystals processed and through a software we can use them to quantify the AE event or even triangulate to find out the source of the AE event. However, there are certain limitations of acoustic emission one is defects which are neither growing nor moving do not produce AE and thus cannot be detected. According to the Kaiser effect only those defects are detected without exceeding the highest preceding load which are already active at the actual load level and are entering the end engineering the component anyway. So only by increasing the load above the previous maximum load level defects can be found which do not grow at standard load. Evaluation criteria do not exist in form of commonly accessible data like the rating of AE results is set firmly to the knowledge and experience of the service provider and AE's testing is very sensitive to noise threshold and noise cannot be stopped and so we have to be very careful about the certain signal to noise ratio and otherwise AE testing is not very deterministic if I may say so unlike vibration monitoring motor current monitoring or even ultrasonic or even the next topic which we are going to discuss is eddy current testing. But AE gives us a quick survey whether a defect has occurred because of stress or not and then we can sense it. So now I will move on to another related another topic in NDT and that is what is known as the eddy current testing. So eddy current of course the first and foremost thing which separates eddy current from ultrasonic testing which we have discussed earlier is eddy current testing is only possible with metals unlike ultrasonic testing which is both for metals and non-metals. So these are some of the applications of eddy current I can measure the metal thickness I can use to sort alloys, find out the heat treatment condition, damage because of heat treatment, the plate thickness or the cladding thickness, insulation thickness, non-metal plate coating thickness, certain vibrations particularly in eddy current proximity probes are used to find out the displacements in turbines or shafts, diameter of tubing or bar stock, cracks, seams, porosity corrosion, erosion, segregation, inclusion all these can be found out in metals by eddy current testing. So let us try to understand how and what is this eddy current testing. So the principle behind this eddy current testing is given in this slide. For example if I have a coil through which I pass usually a high frequency AC signal. So because of this signal being alternating there will be a magnetic field associated in this coil. Now what happens if I bring this coil because of its magnetic field around a conducting material, series of circular eddy currents will be formed. Now this eddy current will also have a magnetic field. Now what happens if there is a defect or change in thickness in this conducting material, the magnetic field produced by this eddy currents will be different and obviously because of Lenz's law this will oppose. So if some way we can detect this difference in the magnetic field because of this eddy current which could be different if there is an foreign inclusion, if there is a defect, if there is a change in thickness this gives us an indirect method to measure the thickness, the displacement of the coil etcetera from the conducting material and so on. So how is this eddy current used for finding out the cracks in a material. For example this is a test coil usually the primary is around 400 hertz or 400 sorry 40 kilohertz very very high frequency signal and then we will have a magnetic field because of this eddy current if there is a crack this magnetic field is going to change and then voltage corresponding voltage would change. Now there are certain relationships as to how close I need to bring this coil to the surface. So there is an relationship between the depth of penetration and given by the magnetic permeability and the frequency of excitation. So all these expressions are there, the eddy current strength is optimum to a certain depth. So eddy current density is greatest at surface and reduces exponentially with depth. So it is good to measure the surface thicknesses or change at the surface. So that is why lot of this coating thicknesses insulation thicknesses we can find out or surface defects or cracks on nice surfaces can be very easily measured through eddy current probes. So there is an effect of frequency if the frequency is high the primary coil in the test coil is frequency of excitation is high the penetration depth is pretty low and if the frequency is low the penetration depth is high and then you can see the proportionate intensity and depth. These are some things which have to keep in mind from this expression here where delta is the depth of penetration. Similarly the conductivity of the material does play a role if the poor conductor be eddy current intensity is different and then with the in a good conductor and so on. Effect of magnetic permeability you can see low permeability and high permeability you can see how the depth and the intensity vary in eddy currents. These are all very qualitative expressions but these equations are also there for different kinds of eddy currents. So what are the parameters by which this eddy current has to be can be influenced one is high frequency high conductivity high permeability one case another case we have low frequency low conductivity low permeability. So and to decide on the right probe for the eddy current the choice of these few parameters have to made the frequency of the primary signal frequency of the primary AC signal which is used to create the magnetic field then the conductivity of the metal and of course the magnetic permeability. So based on this there are different types of probes available if you go to any manufacturer there will be different types of probe depending on how thick material thickness you are going to measure depending on the type of material on which you are going to measure. So all these criteria will let you decide on the selection or let you decide on the type of probe to be eddy current probe to be used for such measurements. Now certain things are also to be noted. So when the suppose of the eddy current from the top view if the cracks are parallel to the eddy currents you will not detect any eddy currents because they are not interrupting the eddy currents. If they are interrupt like in this cross dimension you can see the eddy currents disturbed and then you will get a signal for that. By the way some of these details about this instrumentation can also be found in my website www.iitnoise.com and in our lab we have these measurement facilities both for eddy current, ultrasonic and so on. So you can visit this website to get an update on the instruments which we have. Certain edge effects are also occur. Sometimes edge produces signal just like cracks and misled the inspector. So different techniques can be used to avoid edge effects. So a lot of these NDT techniques you know if you think of thermography, ultrasonic, di-penetrant test, eddy current, acoustic emission a lot of this actually depends on the experience of the operator who is using them in the field to do the measurements. So in a classroom we can very nicely tell you the theories of these measurements but once you go out to the field to do this NDT test techniques many times you will be either misled by poor signal to noise ratios or because you do not have the right kind of transducer to capture the phenomena because if you have a digital signal processing followed by a display unit you know garbage N is garbage out. So we have to very very careful while doing measurements in the field using such techniques which are tested well tested and improved but always I would recommend you know any of you who are practicing NDT techniques for CBM to always do what is known as an in situ calibration of the test equipment and for such NDT techniques there are lot of ASTM standards both for eddy current testing, acoustic emission, ultrasonic, thermography etcetera even certain ISO standards are there ok which need to be referred and sometimes I am we have this kind of standards and at this website. So you can you can have the list of the standards and then of course you can get these standards in your local library or from their websites. So this has to be followed whenever you are doing such NDT techniques testing techniques for CBM. So there is some sort of an inductive coupling between the primary coil and the secondary magnetic field because of the eddy current. So this coupling is what we sense and then we use it. There is another parameter which we have to very careful as to how close should I bring this probe to the surface and that is something defined as the fill factor ok lift off and fill factor ok. This fill factor if you know the diameter D naught and D i. So this D naught square by D i square ok is what is known as the fill factor. Usually 70 to 90 percent of the fill factor is target for reliable inspection. So if you lift off ok this this diameter and this diameter is going to change because of the lift off. So we have to be careful about that we are within 70 to 90 percent of the fill factor for reliable inspection. So what I mean to say you should not be too far away or too close ok. This is the work piece or this is the eddy probe this is the eddy probe. So this distance I meant as the lift off similarly lift off is here. So this depends on the 70 to 90 percent of the fill factor ok. So we have to keep that in mind. So these kind of experiences have come from the analysis in the field and the these are some thumb rules you have to keep in mind while you are measuring the field. And there will be certain phase lag between the surface and the depth of penetration and this can be given by this method. So certain variables comparison we can do. So this is the test variable. So change in the variable and then effect on the surface density and effect on the depth of penetration. So depends on the material conductivity relative magnetic permeability, geometry discontinuity, testing frequency, electromagnetic coupling, coil, current temperature. So these are the variations I will not go into the details. So like I want to say if material conductivity will increase it will have an increase in the surface intensity or the decrease in the depth penetration. So this kind of a table helps one understand which is what to be done so that we have good signal to noise ratio and good measurements. So this is a handy table which somebody can use and keep it in mind for a radio reference. And let me tell you this is something you all can keep in mind and then you can visit them again and again to ensure that you have a good acoustic sorry eddy current measurements. This is how the type of probes which can be used. This is like a surface probe. This is like an external probe like an external coil and this is like an internal probe. You can use eddy current also to measure the internal thickness of tubes and pipes like you can have an eddy current probe going inside a pipeline. So they can be traversing and then you can see. So these are used to measure the wall thickness from the inside. These are the methods like I am the one of the classes as mentioning how we can use an acoustic emission sorry an ultrasonic transducer. But you can also use an eddy current probe if it is a metal tube to find out its thickness this kind of been done. So this mode of operation can be either absolute or differential depending whether it is one coil or two coils you can find out whether it is sensitive, whether it is not sensitive. So this is how we can use this kind of eddy current probe configurations. So these are the views of some of the eddy current probes which you have in the laboratory. These are some of the internal probes, some of the external probes. In fact in vibration monitoring I was also mentioning about the eddy current proximity probe. For example when we have a shaft which is there on a particular turbine shaft which is on a journal. While this is rotating if there is a change in this gap because of an out of roundness this gap and here I can be putting in any of these locations you know maybe I can put an probe eddy current probe such proximity probe and I can measure the gap if it was a sinusoidal it will be essentially a sinusoidal with rotation. So this kind of displacements can be can be measured by eddy current proximity probes and in fact some of this eddy current proximity probes are permanently mounted on turbines at an angle of 45 degree to such probes and you can use them to plot what is known as the orbits is about 90 degree. So you can have an x and a y and you can plot them the signals and then you can you can get a circle or if you can get a point you can get an ellipse. So depending on the phase relationship between x and y you can find out from the orbit plots what is the problem with the shaft which is rotating the machine. Such eddy current proximity probes are also used in turbines or vibration monitoring or displacement monitoring and though here we just explained to you few probes which are used for measuring the coating thickness and so on. And this is a typical eddy current probe with it can have a digital meter or an analog meter which can see the voltage you know this can be all calibrated to a equivalent displacement you can have multi-frequency equipment you know where multiple probes can be done. So certain probes are used or certain calibration standards are available wherein holes and grooves are machined at different percentage of wall thicknesses like this on the inside. So I can move the eddy current probe inside it and then I can see what kind of signals are there. So like I was telling you in all this ASTM standards there are what are known as standard calibration blocks available both for ultrasonic testing I have mentioned about ultrasonic testing in one of the previous classes ultrasonic testing and also for eddy current testing. So whenever you purchase such equipment or sensors for eddy current testing or ultrasonic testing I would recommend that you also purchase a standard calibration block for example then you can calibrate it in the field ok. So some of the testing procedures is balance on the sound portion and then you know because this eddy current probes are actually the signal which we get can be balanced through a woodstone bridge circuit and then you can set the change the resistances to see what are you can balance it by changing the resistances and if there is a difference because of the eddy currents you can sense it through a galvanometer or some sort of a display meter. So effect of frequency on the signal you know you can see. So these are all different calibration standards. So you can see the frequency for high frequency and low frequency this kind of effects can be done. So now you see if you move this acoustic sorry the eddy current probe inside a tube which is made artificially with certain thicknesses you will see converting the eddy current signal to thicknesses. So 0.6 mm, 1.32, 1.98, 2.6, 3.30. So if this kind of in-situ calibration is done it gives us confidence as to whether we are what we are measuring is correct and this is a standard calibration tube which is made available to buy and this can be used to test the deflector. And some of this in a this is another example where we had a tube bottom tube top tube different baffles are there in the tube and then the thickness measurements were done and this can be achieved. So eddy current to summarize is actually used for systems where there is a metal present because when only we have metal there will be an electromagnetic induction between the primary flux or primary magnetic field which will produce a secondary magnetic field and then these two magnetic fields will interact and we will get an EMF according to Lenz's law and these if the material was not metallic I would not never get an eddy current. And few things we have to keep in mind regarding the penetration depth left of good signal to noise ratio is the magnetic permeability, the depth of penetration, the frequency of the signal which has been used to drive the eddy current, the diameter of the coil and so on. This is something which one has to keep in mind. This is another example depending on the crack. So this cross section of the crack which can be very easily detected by moving the eddy current through this can be also done.  We have discussed these NDT techniques so far and few more which we are going to discuss are the radiography or what is known as the x-rays, then we have the dye penetrant testing and of course, the last one the easy one is the visual inspection on places hard to reach. So, we are going to discuss about this in the next class on NDT techniques that will be your lecture number 39. And just to recap almost 10 percent of CBM or condition based maintenance use such NDT techniques. And we just discuss about these four so far in three classes I think this lecture number 36, 37 and this was 38. So, this four lectures would actually correspond to 10 percent of the CBM techniques which are used worldwide. And one has to be coming back to this eddy current testing. One has to be very careful about the frequency, the diameter of the probe and the traversing speed, magnetic permeability. There are few examples wherein such cracks can also be detected by acoustic sorry by eddy current probe. This is another view which I am going to show you is this kind of surface defects on pipes. Now, this kind of surface defects on the pipes can be detected by eddy current testing techniques ok. So, just to recap I mean eddy current is convenient like ultrasonic, but only thing that we are keeping in mind the material has to be metallic. And again lot of this NDT testing techniques lot depends on the skill of an experience of the operator and user of this equipment and mistakes do happen. So, it is always recommended that in-situ field calibration is done while using certain NDT test equipment ok. And then unlike vibration which is very well established where the signals are has have very good signal to noise ratios. They are well deterministic and can be analyzed through automated software and that is the reason why vibration monitoring is used for 70 percent of the machinery for diagnosis throughout the world ok. So, this should bring to a close this lecture. Thank you all.