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Part 2 of 3. How to choose the correct PLC for your application.
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again welcome to automationDirect media we're on to part two of how to select the correct PLC so we're going to go through nine steps of selecting a PLC these nine steps can also be found in our catalog and if you browse around on our website you can find some information of how to select the correct plc for your application and we'll go through and go through these nine steps and hopefully we can help you out with this when we get done we'll give you some resources at the end of part three and show you where you can find more information step one proposed system need to look at a couple of different things new or existing you know if it's an existing PLC how compatible is it if you pull out a brand X and put in a brand Y well the brand Weiss cards work with all the devices out there they're going to be the same ranges are the devices that are you know tied to it gonna work with that new PLC you need to look at well the new PLC fit in the old cabinet stuff like that power requirements most times you're gonna either be using 24 volts DC 120 volts or 220 volts ac for your modules also your power source is going to be the same some people get into low voltage lines or TTL which are usually below 10 volts some of them are very small size constraints like Citizen new enclosure how big of an enclosure can you put in the area how big of a PLC can you put in that enclosure if it's an existing system will your PLC fit in that enclosure and also think of the future you know will the system ever need to be expanded will it need to be networked will it need to have more i/o will it need a bigger PLC if you need a bigger PLC can you put a bigger PLC in the cabinet if not is there room for another cabinet how far will that cabinet have to be so always think of this think ahead environmental temperatures are a big factor had customers that build a system find out the machine or the product is going in some harsh environment could be on a ship deck could be in some very hot environment could be in a very cold environment temperatures are a big issue here so you need to make sure that you are going to be in that range if not you need to think about adding things like either a heater to your enclosure if you're in cold environments or some type of air conditioner or cooling system in the enclosure which we do so the vortex coolers for our enclosures or you get up some of the larger ones you can get air conditioners for them so always keep that in mind there is a spec that any new manufacturer PLC's will put on the PLC if it goes above or below you will see some erratic problems with the processors and so forth dust water and harsh environments class 1 div 2 explosion-proof stuff some customers have to have explosion-proof PLC's or equipment let's just say for instance if you were putting this in a paint booth stuff is very flammable you don't want a relay open and shutting and arcing in a paint booth it could explode so that's just an example we do have class 1 div 2 products code related issues always keep in mind your local and national Electric codes you need to contact your local authorities to find out what those are because every let's just say city might have something different if you're in their city limits discrete i/o okay how many AC and DC inputs are required well let's back up a second discrete i/o what is discrete i/o that just means AC inputs and DC inputs or AC outputs and DC outputs and also relays you have discrete you have analog which we'll get to that in a minute then you get into specialty stuff so discrete i/o we have some voltage you just need to make sure that whatever device you're going to put to the input or the output that it is gonna be in that range so you might have to pick your PLC based on that you might actually have to pick a PLC card based on that what our specific voltages of each like brick PLC's are what we call fixed i/o you either buy it with AC or DC inputs or you buy it with AC DC or relay outputs so if you buy one with AC inputs and relay outputs as we have noted here then that's all you're going to be able to wire up is AC inputs and relay outputs if you find that you've got a DC sensor can't wire it up not without some type of conversion which is gonna make it a little tough modular PLC's you can mix and match the i/o so you can have abundance of sources you know you got AC you got DC whatever you need relay out DC L it can have all that makes the match step four is the analog aya what is analog well analog can be things like our TDS thermocouples as we show here zero to twenty are four to twenty zero to 10 volts plus or minus 10 volts so forth what this is for is let's just say I've got a potentiometer well you need to feed it in and out with analog or let's just say I've got some type of a level switch that's gonna use analog let's say a scale sometimes scales will actually have analog flow meters if it's measuring water passing through a pipe it's gonna use an analog signal so that's when you get into analog some brick units cannot use analog they don't have the availability for let's just say our 105 is fixed no analog on it the 105 when you get into the oh five has one option slot so you could possibly put an analog card in there do 6 you could put analog any of the other peels things you could add them RTD inputs and thermocouple inputs for temperatures and also as you can see here the thermocouples you can use these for millivolt ranges so if you have some really small voltage inputs you can use the thermocouple specialty modules get into specialty modules when we get into high speed counters we have several different high speed counters we have a CTR IO for most of the PLC's including the bricks the CTR int is for the 205 and the HSC we have that for a 405 the bricks offer built-in high speed counters on some modules so any of the bricks the Oh 5 105 and o6 if you buy one that has DC inputs it will have a high speed counter built-in you just wired up those first couple of inputs configure the PLC for and you can read things like encoders positioning servo stepping all that you'd use some high speed stuff ASCII inputs or outputs well what's asking what I need it for or what what I need it for let's just say ASCII you might need it for a barcode reader some scales might use them asking basic programming you might need something special well there's what's called Co Pro modules and these are offered for some PLC's like the 205 and the 405 CPU requirements how much memory am I gonna need well it's tough to say you'd sort of have to guess and say okay am I gonna use a PLC to control one small conveyor and maybe five boxes going down their conveyer now you wouldn't need a whole lot of memory but let's just say I want to control a plant with one PLC and it's gonna have a thousand i/o and it's going to be doing all kinds of tasks with analog and high speed counters and I need to read barcode labels well you're gonna start to eat up some memory when you start writing your ladder logic to program the plc so keep in mind that also everybody's gonna program a little bit differently there's no right or wrong way to get from point A to point B everybody just gets around in a different way so one programmer might be able to program a task using ten lines another programmer might do the same task and use 50 lines so that's always gonna depend on how you program won't depend on how much memory you use as well PID loops well PID what is PID is proportional integral derivative and this is used for analog inputs and outputs and basically let's just a good example cruise control on your car when you get going down the road and you're at 55 miles an hour and you hit set you want your car to stay at 55 if you start going down a hill it's going to try to limit you if you're going up a hill it's going to give it more gas well basically that's what PID would do if you say I want my pump to run exactly at this pump speed then the PID is going to look at your inputs and give you some output based on that and it will change okay if you need PIDs you need to look at different CPUs not all of them have PID floating point math what is that well if you're gonna add things say two plus two equals four you don't really need a big honkin massive CPU with lots of power if you need to get into floating point math and you need to start looking at decimal points well then you need to get up and the higher-level CPUs like 250 260 450 okay nice thing special communications do you think you're gonna need it do you know you if you're going to need it remote i/o you're gonna need to network PLC's to PLC's you need to talk to other devices such as HMI or another say computers or in the plant on a network so forth remote i/o means I have one PLC and it's controlling several other racks of PLC's at other locations or even locally step seven is i/o locations this is a little bit more about the remote i/o basically okay well all of my i/o fit in one rack well let's say that I fill up to a file system and I need more inputs and outputs by another 205 rack put an expansion module in it and a communications module for that and start adding more i/o the first PLC will control the second you can keep adding more as you see this picture over on the right hand side we have a 205 and it has an expansion drop down to another rack drop down to another act drop down to another rack this first PLC is controlling all these racks so you need to make sure that you have all the requirements or you meet all the requirements for this you have all the modules to do this if you need it and keep them on the future expansion stuff you know that sometime in the future you're gonna expand more you know can I use remote i/o do I have the right products 250 or 260 processor you can use expansion or remote i/o either one okay expansion pretty much a plug and go the processor sees all of the i/o and basically you just write the code as you would if all the inputs and outputs were in one PLC system or one rack you need a look at distance of your racks how far apart are they going to be in the 205 expansion you can go up to 90 feet away if you need to go further than that well you're gonna have to go to remote i/o it's a little bit different you have to program for your inputs and outputs that are out at those slave racks but you can go further distances if you need some real far distances you can look at we can get into fiber-optic modules that are master and slave so fiber optic course carries communications a lot further mode i/o when we're looking at that you need to look at what will be my master what will be my slaves how many slave racks and so forth like I said the distance is always going to be an issue how do you run the distance how can you run the wires I've had guys say well I've got to go underneath a river and I only have one piece of conduit and there's all kinds of power wires ran in there well it's not good practice to run communications wires with power if that's the only option you have I'm sorry it's still not good so you need to make sure that you have the proper availability to run what you need to run Communications well as you can see here this one PLC is communicating with a handful of different other outside devices we've got Ethernet going to a switch going to other PLC so it's networked to these PLC's it's going to a drive here we've got a high-speed a counter going to some stuff we've got servos we've got breakout of one Ethernet communications card we're going to another computer and several HMI touch panels we've got barcode readers we've got scales all kinds of other HMIS more drives maybe we come back to a plant computer that's reading all kinds of information over the plant maybe this computer is outside of the plant so it's got to go through some type of communication as you can see here this is a mode on my telephone modem or a modem so it's going through the MDM till modem and talking to a computer so I'm going to make sure that you have all the right communications this can get a little complicated if you're not real familiar so you might have to get some outside help but if networking Ethernet Modbus is a big universal communication device net PROFIBUS and asking likes it ask you stuff like bar codes okay step 9 we're almost at the end here step 9 is programming have a couple of different options when you program our PLC's you can either use software which I highly recommend or you can use a handheld programmer software you're going to need a computer you're going to need to either be able to bring the PLC to your desktop computer or you need a laptop or some way to get your computer out to the plant floor which your laptops great take it out next to the Machine plug it up and you can program or test your program while you're at the machine you don't necessarily have to be out there to program it but to test it you would like to be out there so do you have all this equipment you have laptops held handheld programming all you need is a little handheld and it looks just like this picture here personally I'd rather smite hit me in the foot with a hammer than have to use a handheld programmer there's a lot of people that were trained on these raised on these brought up with handheld programmers that's all they want to use they don't want to touch a computer they don't know how to touch a computer so they're good with handheld programmers but they can be very time consuming trying to figure one out memory modules let's just say for instance did elo five the little break unit you can buy this little d0 - a 1m C which is a memory card or a memory slot and you can pop it into a five you can suck the program onto this little memory module and then you can send it out to your customer I know em could do this you could send it out to your buddy and say hey I've got a new program on this memory module pop it in your oh five and run it so he can pop it in and either he can transfer that program into the memory of his oh five or he can keep it on this memory module and just run off of it so if you make changes for somebody and they don't have the capabilities to either use the software or transfer with software or you just don't want them in there messing with it you can send them this little memory module also there's some chips for say the 405 some of the 405 processors there are little memory chips you can program to those send that little chip out a little our doubt and they can pop it in the processor and let it run off of it so easy way to JT transfer get them a new project out there that we don't have to touch with it okay that's pretty much it for the step nine or the nine steps of choosing in PLC please follow us along to the third portion of this and we'll talk a little bit more about some examples break our PLC's down and also give you some resources
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