PLC Lecture 12 - Data Files vs Program Files - Sinking Sourcing, A PLC Training Tutorial.

now comes the moment that we have all been waiting for the program files the logic the relay ladder logic we are going to cross the line that separates the data files from the Program Files for this family of processors the program files the files that store the sequential logical instructions are labeled latter X beginning with latter two up through ladder 255 this family of processors allows the user to organize their logic into as many as 254 Program Files ladder 2 through ladder 255 ladder to is unique in that it it always executes automatically whenever the processor is the run or remote run modes ladder 3 through ladder 255 however require a special instruction to jump from ladder 2 to their location in memory and to execute them because they are actually subroutines and they are subject to the execution of ladder 2 with data files and Program Files the file numbers are arbitrary for data files you can create new files number 9 up through number 255 and you can have any data file number between without successive data files you can have a data file 47 without having a data file 9 through 46 for Program Files you can create ladder 3 through ladder 255 you can create a program file ladder 15 LED 15 without Program Files 3 through 14 they are markers only like flags on a golf course they can be sequential a number but in truth they only identify the subroutine and can be executed in any order ladder 2 led to led to is the only routine that always executes although memory is memory a different set of rules apply to the working with files below the line than those above the line data files have one set of rules for editing while program files have another set of rules even though the technology to do online editing is the same anywhere in memory the processors in this family processors the ones that do allow online editing do not allow the expansion or contraction of the data arrays in the data table which means everything from the dashed line down can I be altered in size while you are online in the run mode but the Program Files the Lanter logic itself in some of the processors in this family you can edit and change those online the smaller processors in this family of products with the exception of the newest one do not allow online editing the larger modular processors do allow online editing but none of these processors allow you to shift the size or shape of the data table files much less create a new data table file while online with a processor you can expand contract and create new data table files offline only you can edit the logic online but not create a new program file online with the newest family of processors not covered in this presentation you can do almost anything online and in the run mode while we are on the subject of being online with a processor let's briefly introduce the project or program documentation what we refer to as the man readable stuff the stuff that we see on our computer screen the text without which we feel lost by now you have realized that the variable be 3 : 0 a 16-bit integer was designated before any i/o data structures were added to the memory layout which would have moved the actual location to be 3 : 0 to a higher location of memory and yet this thing that most of us refer to as an address remains the same and of course this is because it is not an address but a variable and when it gets moved around the process is invisible to us the variable name doesn't change but the memory location that it points to changes the most accurate explanation of this relationship between the variable and the memory location is this when you download the memory layout is translated into real memory locations the actual program that downloads to the processor is in machine language a language that most of us do not understand the language that we created this program with the program files the data table files is graphics based and what downloads to the processor is entirely obscure to us let's pick a single bit B 3 : 0 / 0 from the variable B 3 : 0 and look closely at the nomenclature first of all we cannot see the real memory location or the real memory ID it's numerical it's probably in hex code we use a variable pointer operand or tag name also referred to as an alias this is an alias for the real memory address since we never see the real memory address we'll stick to variable tag name pointer operand because later on we will create an alias for the variable or the tag name many find the default variables to be in conveniently named they represent positions in a numerical array and that alone allows us to know where the bit is located in memory structured by its variable name however when the bit is use in your logic and comes to represent whether or not the machine is in the manual mode B 3 : 0/0 means nothing to anyone trying to analyze the logic for this reason the manufacturer of the programming software allows us to assign an alias to the variable that is more indicative of the use of the bit for this programming software they have chosen to call the alias a symbol the symbol is unique to one variable and the software will not allow you to assign the same symbol name to other variables once it has been used so you could say the symbol and the variable name are interchangeable when you are creating logic you can type in the symbol and it will bring the base variable with it with this programming software the symbol is limited to a single line of 20 characters if more descriptive nomenclature is needed this programming software allows you to add a description and associate it with a variable although I show only three lines the descriptions are limited to five lines of 20 characters almost enough to write a book the programming software will not inhibit you from assigning the same description to two separate variables so beware it's not like the symbol where it will prevent you from using the same symbol twice it will allow you to put anything you want in those five by twenty characters for the description now this is a very important point that I want you to remember and not forget this and that is this the symbols and the descriptions reside on the hard drive and in your laptop's RAM but the symbols and descriptions are never downloaded to the processor this means that if you write the program on your laptop download the program into a processor on a machine ship the Machine off to Timbuktu and then someone in Timbuktu connects their laptop to this processor and goes online or uploads with another laptop there are no symbols and no descriptions for them to see you have to send the offline file along with the processor for them to open first in their PC or their laptop before they connect and go online another point there are no online projects only offline projects you can go online from within and offline project download and upload from within an offline project if you do not have an offline project for the program in a PLC when you connect to it you will find this out you will then have to create a new offline project then from within the newly created offline project upload and go online the PLC is just one component of an industrial control circuit how does it fit in with some of the other components such as in MMI or operate interface the screens as people refer to them well folks you're looking at the whole shebang here I have added a few external influences to enhance our story you Larry laptop feet panel of you repeat panel view and repeats other brother repeat panel view while there are some inexpensive processors such as the one used in the training manual that do not have two communication ports most have two communication ports as shown here we have you Larry laptop connected to channel zero and we have several man-machine interfaces networked to channel 1 channel 0 is typically rs-232 and uses the DF 1 D H 45 protocol whereas channel 1 can be an addressable D H 45 and addressable data Highway plus or even better yet Ethernet the CPU central processing unit is central to everything that happens the kingpin we ought to mention that the firmware has an active role in this process and that there is another chunk of code called the executive that is really the primary execute which in turn executes the code that we have downloaded our code that we have created does not have instructions to go retrieve the input image information etc that is the realm of the executive code which we cannot access what exactly does this executive code which is built into the processor do for us when we first put the processor into the run or remote run mode the first thing the executive does after a little housecleaning is to activate the input modules on the backplane one at a time and second to order and store the images or input status of each of these modules into the memory locations designated for each slot in the input data table file one how long this takes is dependent solely upon the quantity of words that have to be activated one at a time onto the backplane it's transferred into memory locations remember some of the processors in this family allow 30 possible slots of i/o that slot 1 through slot 30 and each slot is capable of transacting 32 words n and 32 words out that is 920 words one at a time over the backplane in to the PLC's data file number one and then another nine hundred and twenty words transferred out of the PLC's data file zero to the individual slots that have output cards one word at a time once the processor has a fresh snapshot of the input states it begins accessing the logic one rung at a time the processor grabs a rung of logic which is comprised of instructions each of which have a memory location that they address and reads the value from each of these memory locations into the processor crunches the logic and with its logical relationship to the values in each of the locations that each instruction addressed then spits out the results to the memory locations that were addressed by the output type instructions this is followed by activating the output modules one at a time sequentially over the backplane and transferring the data from the controller's memory to each module associated with that word of memory to control the output devices this is the primary cycle that people identify with the PLC collect inputs execute the logic storing the results and then sending out the results to the output modules but before the CP retrieves the next input image the communications functions are seen - we have Larry laptop Pete panel view and his two brothers to communicate with unknown to most these entities out there connected to the con ports have equal access to all of the memory locations that the program has access to any memory location that has an instruction and address the laptop can alter from the keyboard the MM is read from a write to them as well let me say that one more time any memory location that has a variable the laptop can access that variable from the keyboard the MMIS can access that variable as well as the program can access that variable so at any given instant I would say within a one-second period somebody at the laptop somebody at an MMI and the program itself could be changing the state of bits in that memory in this industry we refer to this type of system as having naked data that means that while you are intently troubleshooting this machine a board operator can be walking by poking buttons at random and changing the data in the data table even changing the screen on an MMI can change a variable in the PLC and of course Larry laptop which should be you can change any of the variables directly from the keyboard the the characteristic of this type of controller that really identifies it as having naked data is that you can plug another PLC into one of these comport s-- and by a means of a message instruction read anything from this memory and write anywhere into this memory without this controller needing to give the other controller permission one of the simplest and yet most often misunderstood terminologies in this business is the concept of syncing and sourcing first syncing and sourcing only applies to DC Circuit's and is of no concern with AC inputs and outputs every DC circuit has a minimum of these four basic elements the positive source of voltage the negative common or sync side of the voltage a load which is the object of the DC power supply and a means to control the loads such as a switch now we've assembled these four elements into a circuit we have the high side of the supply or the positive side we have a load we have a switch to control energized energized of the load and then we have the sync or low side of the power supply pure and simple of the two devices the load of the switch the closest device to the source or positive side of the power supply is sourcing and the device closest to the sink or negative side of the supply is syncing if you swap the control switch and the load positions in this circuit the switch is now sourcing and the load is sinking it's that simple whichever of the two the controller the load whichever the two is closest to the source is the source which ever is closest to ground or the sink is the sink sourcing syncing you're probably looking at this comparison here and wondering what the big deal is and why it even matters remember that the control device in this illustration is a dry switch contact not a solid-state device such as a transistor so in this case that switch same switch can be used in either position as a sourcing input device or a sinking input device now let's look at an actual input circuit you should recognize this from a previous illustration of previous presentation now if you don't recognize this go back to the earlier sections on the active backplane review them and then come back here and watch the section again first thing to point out is that the sensor has an open collector NPN interface to the input circuit of the input module so you could say the output of the sensor is open collector therefore it has to be syncing it has to be on the low side of the circuit the input circuit of this module is the load and the sensor is the switch V sub C C or the positive side of the supply and ground the negative side of the supplier sync between the input circuit of the input module and the sensor which would you say is sourcing which is closer to the source not a trick question just an easy question that is correct the input circuit of the module now which then is closest to the sink now that's too easy because there's only one left right yes the sensor so in this circuit we have a sourcing input module that requires a syncing sensor or an NPN sensor in this circuit the sensor and the input circuit happens have been swapped around in their relationship with the source and the sink again which of the two is closest to the source you got it pretty simple huh and of course what is left to be the syncing device yep the input circuit of the input module it is important to point out here that I have used a universal input module that will accept either syncing NPN sensors or sourcing PNP sensors however here's the fly in the ointment of this whole sourcing syncing discussion every circuit has a sink and a source so when you are identifying the input module do you identify it by where its circuit fits in the DC circuit or by what type of a sensor that you apply to it is it a syncing module because it's its input circuit sinks the sensor or do you call it a sourcing module because it requires a sourcing sensor to be sure with different manufacturers you need to look at the wiring diagrams in the manual that come with the modules to make sure before you actually connect sensors well that's all folks but wait there's more what is this thing on December 16th 1947 routine and Bardeen under the direction of dr. Shockley built this point contact transistor this is actually a photo of the original point-contact transistor made from strips of gold foil on a plastic triangle you can see the plastic triangle right there in the middle push down into contact with a slab of germanium later dr. Lee dr. Shockley himself designed and built the first bipolar transistor that remained the mainstay of the industry for three decades now Bell Labs decided to announce the invention on June 30th 1948 there was some time lapse between the point-contact transistor in the actual announcement bill Labs settled on the name transistor combining the concepts of trans resistance with the names of other devices like thermistors the invention went unnoticed at the time both in the popular press and in industry however Shockley saw his potential he quit Bell Labs and founded Shockley semiconductor in Palo Alto California he hired the best engineers and physicists but Shockley's personality drove away eight of his best and brightest those eight engineers founded a company called Fairchild Semiconductor two of the eight went on to form Intel Corporation they and others have texts instruments together invented the integrated circuit Shockley's company was the beginning of Silicon Valley in the 1950s and 60s most US companies chose to focus their attentions on the military market in producing transistor products which left the door wide open for our friends the Japanese like Akio Morita Emmas sorry he bucha who founded a company named sony electronics that mass-produced transistor radios this was the form of transistors took for the first couple of years and it pretty much stayed in this form for a decade or two this is called a top-hat transistor and if you look inside you'll see the lid has been cut off to expose two of the three terminals coming up from the base and you'll see two fine wires going over to a little square with a little white spot in the middle of it that is the actual transistor right there the actual transistor device is much much smaller than the case that it was mounted in a closer look reveals the actual device was a half a millimeter square with two leads delicately soldered to the emitter and the base of the device let's take a more in-depth look at exactly what a transistor is this next sight track discussion here is information outside the scope of this training package but it is of great interest to enough of you to include it in the miscellaneous sections of this presentation first some background the Bohr model of the atom in front of you will be sufficient for the basis of our exploration of the subject an atom a single atom is so small that no one has actually seen an image of one atoms are so small that millions of them would fit on the head of a straight pin this simplified illustration has all the basic components of an atom the nucleus made up of neutrons and protons in a cloud of electrons orbiting around the nucleus it is key to note that there are an equal quantity of each this atom has 3 neutrons 3 protons and 3 electrons the neutrons are considered to be of neutral charge and theoretically a neutron is made up of one electron and one proton but well to say it's a neutral charge and part of the mass whereas protons are positive and the electrons are negative in charge and as you know equals and opposites attract the electron is negative the proton is positive they are attracted to each other but because of the energy levels of atoms under normal temperature the electrons are energized by that energy and are trying to fly away from the nucleus but the proton being positive holds the electron in its orbit around the nucleus the equal quantities of electrons as negative charges and protons as positive charges give the atom a net balanced electrical charge with no electrical field emanating from the atom this is a graphical representation of a single silicon atom showing a full count of protons and electrons notice that this atom has three levels of orbits each represented by in an ellipse from a small ellipse to a mid-sized ellipse to a large ellipse notice that this atom with its three levels of orbits the innermost has two electrons the intermediate orbit has eight electrons and the outer orbit which is called the valence ring as it is referred to has four electrons silicon is said to have a valence of four the outer orbit has four electrons that's the valence orbit therefore it has a valence of for the valence electrons those in the outer orbit are all we are concerned with when discussing semiconductors so let's simplify our atom to show just the valence electrons okay so this represents a silicon atom with four electrons in the valence ring we put a Roman numeral four on the periodic chart it would fall under the column of four silicon is actually an excellent insulator so we will need to modify this substance to make it a semiconductor and we will do this by working with boron which is a trivalent it has three electrons in the outer orbit I show a fourth little spot there as a dashed line just in reference to the fact that it only has three and then of course also arsenic which has five electrons in the outer orbit so here we have a trivalent a quadrivalent and a pentavalent material silicon is our base material but we're going to work with the impurities of boron with three electrons in the outer orbit and arsenic with five electrons in the outer orbit okay pure silicon represented here as a crystalline structure a lattice each atom having four valence electrons for reasons we'll outside the scope of this discussion a valence of eight electrons is the optimum situation for silicon or for an insulator in other words each atom would like to have eight electrons in its outer orbit in this structure you can see a lattice of silicon atoms each with four electrons in their outermost orbit and although there are only four in each of the atoms outermost orbit those four electrons find themselves in the company of electrons from the surrounding silicon atoms valence electrons they form up into pairs and now each Anna behaves as if it had eight electrons in its outermost orbit this behavior is called covalent bonding this is silicon what about the other two players in this story boron and arsenic let's allow an impurity a boron one atom of boron into our lattice of silicon we still have covalent bonding but notice the binding of an atom of boron into a structure of silicon the three electrons of the boron atom bond to the three electrons of surrounding silicon atoms but one of the surrounding silicon atoms is left without an electron to bind with this electron is firmly held in place to the silicon atom by the protons in the atom but this leaves a hole so to speak in the lattice perfection in other words in the lattice structure if you look at the whole structures as a complete entity this one spot where this one boron atom has made it up it's three valence with three surrounding silicon Adams's it leaves a hole for one of the silicon atoms however the electron that didn't bind up it's firmly attached to that silicon atom to the proton of that atom but it leaves a hole in the structure that would kind of like to have electron to fill it up because the hole wants an electron we say that it has a positive charge and therefore this silicon substance doped as they say with boron is said to be p-type silicon typically one atom of doping substance per 100 million silicon atoms so we're not talking about a high density of boron added as an impurity to silicon one in a hundred million now let's consider arsenic here is one arsenic atom as an impurity notice that every atom has total covalent bonding but now we have a lonesome electron with no no one hang out with no electrons to bond with this electron is not an extra electron because it is there to balance the net electrical charge of the arsenic atom but in the big picture it is looking for a place in the structure electrons are negative so it is no surprise that we refer to silicon doped with arsenic to be n-type silicon now typically it's one atom of doping substance per hundred million silicon atoms however when they actually manufacture semiconductor material transistors there is they use different doping densities between the emitter base and collector to get what they call transistor action we'll look at that a little bit later okay how do we make a transistor well let's start out with a substrate of n-type silicon and build a thick layer of p-type silicon through high vacuum deposition now basically what that means is they put it in a vacuum change chamber pull all of the atmosphere out drop it right down to a micron a vacuum in other words no gas molecules float around then into the chamber they inject vaporized silicon and vaporized boron and this material settles and builds as a structure on top of the silicon doped with arsenic so it gives you a layer of boron doped silicon on top of the layer of silicon doped with arsenic okay after they do that then they also by photographic itching apply a mask that leaves areas exposed where they want to do more work on the p-type material the next step is to use a corrosive chemical to etch a well into the p-type material and notice that it only etches where the masking material was not so the black represents the masking material the next step is another high vacuum deposition and they deposit n-type silicon and the mask prevents it from going anywhere but inside the well once the well is built up then the Reem asked to protect all of the p-type material and a large portion of the n-type back into the process a corrosive chemical etching away another well into the n-type material back into the process again through high vacuum deposition they deposit a layer of p-type material into the well that they just etched and the last step is to then connect electrical contacts to the p-type material in the middle and that's the emitter and then another contact to the n-type material between the two P types that's the base and then the collector and you'll you probably will notice here you probably won't take note but take note that the collector surrounds the emitter now the base surrounds the emitter but later on when we talk about transistor action when the emitter emits current carriers into the base because the collector surrounds that whole area it's easy for the collector to collect those current carriers that were emitted by the emitter so pnp and npn transistors now you see why they call it P type material and n-type material because the current carriers are either holes or lonely electrons and I'm paraphrasing a little bit here but hang with me so the difference between a PNP and NPN is simply the construction and material supplies electrons P material supplies holes both configurations PNP or NPN have three connections the emitter the base and the collector the actual circuit symbol for a transistor will have an arrow representing the emitter the direction of the arrow always points to the n-type material so you see on the right you have a symbol for a transistor and the emitter has an arrow pointing to the base the basis n-type material now this is not the reason that they have the arrow pointing to the base they have the arrow pointing to the base because the arrow is pointing in the direction of conventional current flow or hole flow I'm not going to stop and explain the difference between conventional current flow and electron flow any more than saying that originally they thought that current flowed from positive meaning and access to negative meaning a deficiency and so it kind of stuck so hole flow is what's represented by the arrow conventional current flow not electron flow so the arrows pointing enough to represent a flow going from positive to negative okay the NPN also has a symbol and notice the arrow points towards the emitter because the emitter is n-type material and that is the direction of conventional current flow the reason I'd like to point out that the arrow points to the end material that's how you remember what these symbols are so when you see that top symbol the arrow points to the base the base is n-type so its PNP the bottom symbol the arrow points to the emitter therefore it's in PN okay that's real interesting but how does the transistor actually function let's examine a single junction of p-type and n-type silicon brought together first we'll start with the n-type and then we'll form a junction with a p-type material to an n-type material when we do that it's going to form a depletion region or a depletion zone basically what happens is current carriers diffuse from the p-type material into the n-type and the n-type into the p-type so there's an exchange of current carriers between the two different types of doped silicon so when the when the two materials are brought together a depletion region forms spontaneously across the PN Junction electrons and holes diffuse into regions immediately adjacent to the junction until they are uniformly distributed n-type material or n-type semiconductor has an excess of free electrons compared to the p-type region the p-type has an excess of holes compared to the n-type region therefore when the n-doped and P doped sections of semiconductor are placed together to form a junction electrons diffuse into the P site and holes diffuse into the inside upon the departure of an electron from the inside to the P side a positive donor ion is left behind on the inside remember if an electron leaves a electrically balanced atom that leaves behind a proton which is a positive charge that has no electron to balance it therefore that atom will appear as a positive charge they call it a donor ion in this case it's positive in a slept behind on the inside and likewise when the hole departs from the inside it leaves a negative accept on the p-side so when I hold the parts for the inside it leaves a negative donor ion on the P side following diffusion of the majority current carriers across the junction the electrons come into contact with holes on the P site and are filled by recombination so in other words these electrons went over and eventually fell into the holes that we showed you earlier that's called recombination likewise for the injected holes when they arrive on the inside the net result is that the injected electrons and the holes are of none effect but leave behind charged ions adjacent to the interface in a region with no majority current carriers called the depletion region it's called the plea ssin because all the majority current carriers have been depleted in that region but there is also a charge across that region caused by the donor ions that were left behind this creates an electric field that provides a force opposing any additional diffusion of charge carriers in other words what drew them across was satisfied by what came across and what came across creates an electric field a charge that opposes any further transport or exchange so it builds up to an equilibrium this electrical field that extends between the charged ions is referred to as the building voltage junction voltage or barrier voltage so let me summarize current carries from the p-type drift over into the n-type drawn by the n-type n-type carriers drift over into the p-type they recombine meaning the electrons fall into holes therefore in the holes that went the other direction cancel out the electrons so there are no current carriers now in that entire depletion region that there's a charge left by the donor ions that were left behind okay let's freeze this in an instant in time right here and let's say we just connected this single cell DC battery up to a PN Junction if a direct current voltage is applied across the junction positive to the n-type material and negative to the p-type material electrons will flow from the negative side of the battery into the p-type material and it will the positive side of the battery will pull electrons out of the negative side notice what that does those electrons that are injected into the pink side the positive side they will travel over to the junction and further increase the size of the depletion zone whereas the electrons drawn off the gray or n-type material pull more electrons out of the area adjacent to the joint on the inside the grey side further increasing the depletion zone so you see our little blank gray and pink areas increased in width caused by the battery now what's going to happen here remember that as you increase the depletion region size you're increasing the number of positive and negative donor ions on each side that builds up a charge or voltage across the junction the barrier voltage when it equals the battery voltage everything stops this is called reverse biasing a PN Junction so remember this later on when you hear reverse bias forward bias that's what they're talking about now let's do just the opposite let's flip the voltage around so we have the negative side of the battery applied to the n-type material and the positive side of the battery applied to the p-type material electrons flow from the negative side of the battery are injected into the n-type material and electrons are pulled away from the positive side of the p-type material this causes more free electrons to go across the junction into the p-type material and eventually you have a steady state flow of electron majority current carriers through the junction now you could also say that you have positive carriers flowing in the opposite direction I tend to always work with electron flow you could also show this with hole flow because the positive side does inject holes into the p-type material but in order to get this to work you have to have equal transfer of the current carriers from the N and the P type material this is called forward bias okay this is kind of a catch-all diagram of a bolt bipolar Junction transistor that referred to it as a BJT bipolar Junction transistor in a a bipolar Junction transistor is a type of transistor a BJT bipolar Junction transistor is a three terminal device constructed of doped semiconductor material and it can be used for amplifying or switching applications bipolar transistors are named so because their operation involves both electrons and holes as opposed to a unipolar transistor such as a Fe T or field effect transistor in which only one carrier type is involved in the charge flow it's a whole different construction than what you're looking at right here this diagram is one that I got off the internet it's public domain and a real in-depth discussion of this is really way outside the scope of this presentation however because there is a lot of interest in PN P and PN well what does that mean and how do they work I'm going to go ahead and do a little discussion with this diagram if at the end you don't completely understand everything we talked about don't worry about it it's not germane to programming a PLC or troubleshooting a PLC anyway okay although a small part of the transistor current is due to the flow of majority current carriers which we discussed most of the transistor current is due to the flow of minority carriers so bipolar Junction transistors are classified as a minority carrier device now what's the minor minority carrier well n-type material has free electrons and those are the majority current carrier any hole flow in an n-type material is considered minority current carriers so electrons are majority in the n-type and minoring the p-type so holes then are majority in the n-type minority in the p-type in typical operation the emitter base Junction notice you have an e Obinna C symbols there so on your left is the emitter on your right as the collector notice that in an NPN electrons flow from emitter to collector and then in the middle you have the base so when they say emitter base Junction they're talking about the junction between the green and the blue on the left the collector base our base collector Junction is the junction between the green and the blue on the right the power supply between the emitter and base which is the VESA be e to the left down below the transistor that is the forward bias voltage to forward bias the emitter base Junction the higher voltage V sub C be voltage collector base is the reverse bias voltage for the collector base Junction right above it both of those batteries together in series these to be e and V sub C be supply the current flow that goes in the emitter and out the collector and back now in typical operation the emitter-base junction is forward bias and the base collector Junction is reverse bias in an NPN transistor for example such as this one when a positive charge is applied to the base emitter Junction the equilibrium between the thermally generated carriers and the repelling electrical field of the depletion region where we call that a barrier voltage becomes unbalanced allowing the thermally excited electrons to inject into the base region these electrons wander or diffuse through the base from the region of high concentration near the emitter towards the region of low concentration near the collector the electrons on the base are called minority carriers because the base is doped p-type which would make holes the majority carrier in the base the base region of the transistor has made very thin so that the current carriers that diffuse across it in much less time than the semiconductors minority carrier lifetime now what that's basically saying is you make the base the green material really thin compared to the blue material that way when the electrons get injected in from the emitter they drift over towards the collector and have a chance to get to the collector before they recombine in the base now once the coat the the electrons the free electrons the drifted over to the base because of the forward bias of the base emitter emitter base Junction if they get close enough the collector the positive charge in the collector will reach out and grab them and pull them in the collector so you could say that the electrons that were injected into the base from the emitter are collected by the collector and go back to the battery that represents the majority of the current flow going through but this depends upon the proper ratio of density of doping between the base material the emitter material the base material on the collector this is a lot to take in in what I'm going to give you here but we're taking a shot at this get what you can out of it as I said the base region of the transistor is made very thin so that the current carriers can diffuse across it in much less time then the semiconductors might in order to carry your lifetime to minimize the percentage of carriers to get that reget recombine before reaching the base collector Junction in other words we don't want to give the minority carriers time to find a home before they drift close enough to the collector to get collected or the the majority current carriers to ensure this the thickness of the base is much less than what's called the diffusion length of the electrons don't worry about what that is but you get the idea the base is purposely doped a little less dense and it's made thinner to provide this transistor action the collector base Junction is reverse bias so little electron injection occurs from the collector to the base but electrons that diffuse through the base towards the collector are swept into the collector by the electric field in the depletion region of the collector base Junction so the collector emitter current which is the main current flow can be viewed as being controlled by the base emitter current or by the base emitter voltage by the bias voltage the portion of electrons able to cross the base and reach the collector is a measure of the bipolar Junction transistor efficiency the heavy doping of the emitter region and the light doping of the base region caused many more electrons to be injected from the emitter into the base than holes to be injected from the base in the emitter so basically because of the difference in doping and the difference in size when the transfer take place a lot more electrons go into the base than holes go into the emitter well these electrons have nothing to recombine with they drift over come under the influence of the collector base enter collected into the collector the heavy doping of the emitter region and the light doping of the base region caused many more electrons to be injected from the emitter into the base than holes to be injected from the base into the emitter the common emitter current gain is represented by the symbol beta it is approximately the ratio of DC collector current to DC emitter current gain let me repeat that it is approximately the ratio of the DC collector current to DC base current in forward active region so if you take the current going through the base into the emitter versus the current going all the way through minuted collector that would be the gain so if you were looking at amplification the ratio of the collector current to the base current would be the beta basically and typically that's around 100 which means that as you control the current flow into the base the emitter collector current flow will vary in proportion to that base current if the collector current is typically a hundred times higher than the base current that gives you a current gain of 100 now I'm paraphrasing and cheating a little bit in the explanation I just want to give you a kind of a fuzzy view of transistor action so this current ratio it is approximately the ratio of the DC collector current to the DC base current in forward active region and is typically greater than 100 another important parameter is the common base current gain or alpha the common base current gain is approximately the gain of current from emitter collector in the forward active region this ratio usually has a value close to unity or one and typically it's going to be a little less than one so it's around point nine eight two point nine nine eight so basically you're saying that it's the ratio of the collector current over the emitter current now since some of it recombine is lost in the base the collector current will never be as high as the emitter current because some of it goes through the base so it's always going to be just a hair less than unity or one alpha and beta are more closely or more precisely related by the following identities of an NPN transistor okay don't worry about the following identities that's a little more than I wanted to do in this discussion so a bipolar Junction transistor consists of three differently doped semiconductor regions the emitter region the base region in the collector region these regions are respectively P type and type p-type in a PNP or n-type p-type n-type in an NPN as seen here in this diagram each semiconductor region is connected to a terminal appropriately labeled emitter base collector the base is physically located between the emitter and collector and is made of lightly doped high resistivity material the emitter is heavily doped while the collector is lightly doped now we don't want the collector highly doped because we don't want it emitting into the base so the collector is lightly doped allowing a large reverse bias voltage to be applied before the collector base Junction breaks down so if we highly doped the collector and then put a notice that V sub C B is larger than V sub B the collector base power supply has two cells where visa b e only has one that's just to imply that it's a larger voltage if we had heavily doped the collector and put a high reverse bias voltage on the collector base then it would break down and conduct we don't want that it would avalanche and conduct the collector base junction then is reverse bias in normal operation the reason the emitter is heavily doped is to increase the emitter emitter injection efficiency the ratio of carriers injected by the emitter to those injected by the base that's the gain for high current gain most of the carriers injected into the emitter base Junction must come from the emitter small changes in the voltage applied across the base emitter terminals the E and B terminals causes the current that flows between the emitter and the collector to change significantly significantly this effect can be used to amplify the input voltage or current bipolar Junction transistors can be thought of as voltage controlled current sources but our more simply characterized as current controlled current sources or current amplifiers due to the low impedance of the base this is a silicon transistor but early transistors were made of germanium but most modern bipolar Junction transistors are made from silicon a significant minority are also also made from gallium arsenide especially for very high speed applications NPN is one of the two types of bipolar transistors in which the letters N and P refer to the majority charge carriers inside the different regions of the transistor most bipolar transistors used today are NPN because electron mobility is higher than hole mobility in the semiconductors allowing greater currents and faster operation therefore NPN is a Serperior bipolar Junction transistor - the PNP BJT the arrow and the NPN transistor symbol is on the emitter leg and points in the direction of conventional current flow when the devices in forward active mode PNP transistors consists of a layer of n-doped semiconductor between two layers of p-doped material a small current leaving the base in common emitter mode is amplified in the collector output in other terms a PNP transistor is on when its base is pulled low relative to the emitter the arrow and the PNP transistor symbol is on the emitter leg and points in the direction of conventional current flow when the device is in the forward active mode okay I know that was a whole lot real quick and I fumbled with my words in a few spots but I hope you get the general idea of transistor action in a kind of a quick little summary here we have an emitter a base to collector the emitter emits current carriers into the base because the base is more likely doped than the emitter they can't all join up and recombine so some of them got to go so place someplace and they drift over because the thinness of the base they quickly get over to the base collector Junction to the depletion zone in our pulled over end of the collector and collected so the collector current is always slightly less than the emitter current by whatever current is actually flowing in the base so all of the current goes through the emitter and then some of the goes to the collector some of the goes to the base the ratio of the current in the collector to the current and the base you could call the gain or the amplification so you vary a real tiny current this emitter base current that causes a larger current a hundred times or more larger going from the emitter collector to vary in step with the current this varying emitter base that's how you amplify you put in a small current signal you get out a large current signal that is varying in step with the base current therefore amplification okay NPN or PNP that's always a discussion Japan uses almost exclusively NPN here in the states people tend to like PNP the input circuit on the top is a PNP you see a PNP symbol and on the bottom that's an NPN now for the PNP if back in the old days when you went out measured a sensor with ammeter the sensor to ground if the sensor was conducting you would measure voltage you would get voltage and the sensor wasn't conducting you would get zero volts okay if the sensor is not conducting then the 24 volts is felt across the open circuit which is the sensor it's not on whereas down below the NPN if the sensor is conducting you're going to may use your zero volts and if it's not conducting to mater 24 and back in those days the people that perform the majority the maintenance on this equipment if the sensors on they like to see a voltage and if it's off they don't want to see a voltage so you can see here that PNP sensors when the sensor is conducting you're going to measure 24 volts DC from the sensor output to ground because the sensor is very low impedance so the 24 volts is felt at the input of the module to ground whereas the second example with the NPN sensor when the sensor is conducting the sensor has a very low impedance and the 24 volts is filled across the input circuit which is not what you're measuring your marriage measuring from the sensor output to ground you're going to measure 0 volts DC are close to it when the sensor is conducting and when the sensor is not conducting you're going to measure 24 volts DC so let's say you add both NPN and PNP out there well when you go out troubleshoot with ammeter you're going to have to know there is PNP or NPN sourcing or sinking to determine which is on and which is off for PNP on is 24 volts for NPN off is 24 volts or you could say for PNP on is 24 volts measured from the sensor to ground for the NPN measure from the sensor to ground on is 0 volts DC take your pick well that's all folks really that's all she wrote you

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Keywords: Lecture, 12, Data, Files, vs, Program, Sinking, Sourcing, Semiconductors, PLC, Programmable Logic Controller, training, tutorial, hands on, programming, learn, Learning, Lesson, AB, Allen, Bradley, Rockwell, Automation, free, download, courses, course, ladder, ladder logic, Micrologix, SLC, 500, inputs, outputs, troubleshooting, basic

Id: ARSSLnTYoQc

Length: 69min 19sec (4159 seconds)

Published: Thu Feb 23 2012