Selecting a PLC - General PLC Knowledge - Part 2 from AutomationDirect

again welcome to automation Direct Media we're on to part two of how to select the correct PLC 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 uh 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 uh 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 um will the brand y's cards work with all the devices out there are they going to be the same ranges are the devices that are you know tied to it going to work with that new PLC um you need to look at will the new PLC fit in the old cabinet stuff like that power requirements um most times you're going to either be using 24 volts DC um 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 I said is a new enclosure how big of an enclosure closure 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 this system ever need to be expanded will it need to be networked will it need to have more IO 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 uh 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 uh cooling system in the enclosure which we do sell 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 manufacturer plcs will put on the PLC if it goes above or below you will see some erratic problems with the uh processors and so forth dust water and harsh environments class one div 2 explosion proof stuff some customers have to have explosion proof plcs or equipment let's just say for instance if you were putting this in a paint booth um 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 one div 2 uh 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 IO okay how many AC and DC inputs are required well let's back up a second discrete IO what is discrete iio that just means AC inputs and DC inputs or AC outputs and DC outputs and uh also relays um you have discrete you have analog which we'll get to that in a minute then you get into specialty stuff so discrete IO we have some voltages you need to make sure that uh whatever device you're going to put to the input or the output that it is going to 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 are specific voltages of each like brick plc's are what we call fixed IO 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 got a DC uh sensor can't wire it up not out some type of conversion which is going to make it a little tough modular PLC is 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 out you can have all that mixed and match step four is the analog iio what is analog well analog can be things like rtds thermal couples as we show here 0 to 20 or 4 to 20 0 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 uh in and out with analog or let's just say I've got some type of a level switch that's going to 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 going to 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 it let's just say our 105 is fixed no analog on it uh the 105 when you get into the 05 has one option slot so you could possibly put an analog card in there the 06 you could put analog any of the other plcs you could add them RTD inputs and thermal couple inputs for uh temperatures and also as you can see here the thermal couples you can use these for molt ranges so if you have some really small voltage inputs you can use the thermal couple specialty modules get into specialty modules when we get into high-speed counters we have several different high-speed counters we have a CT iio for uh most of the plc's including the bricks the CT n is for the 205 and the HSC uh we have that for a 405 the bricks offer builtin high-speed counters on some modules so any of the bricks the 05 105 and 06 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 it and you can read things like encoders positioning Servo stepping all that you use some highspeed stuff asky inputs or outputs well what's asking and what I need it for what would I need it for um let's just say asky you might need it for a barcode reader some scales might use some to asky 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 going to need well it's tough to say you need to sort of have to guess and say okay am I going to use a PLC to control one small conveyor and maybe five boxes going down there conveyor now you wouldn't need a whole lot of meory memory but let's just say I want to control a plant with one PLC and it's going to have a th000 IO 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 going to start eating up some memory when you start writing your lad logic to program the PLC so keep in mind that um also everybody's going to 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 10 lines another programmer might do the same task and use 50 lines so that's always going to depend on uh how you program will depend on how much memory you use as well P Loops well P what is p it's proportional integral derivative and this is used for analog inputs and outputs and basically let's just uh good example cruise control on your car when you get going down the road and you're 55 miles 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 p is going to look at your inputs and give you some output based on that and it will change okay if you need P IDs you need to look at different CPUs not all of them have p floating Point math what is that well if you're going to add things say 2 + 2 equals 4 you don't really need a big honken 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 in the higher level CPUs like 250 260 450 okay next thing special Communications do you think you're going to need it do you know if you're going to need it remote IO you're going to need to Network plcs to plcs you're going to need to talk to other devices such as HMI or another say computers are in the plant on a network so forth remote IO means I have one PLC and it's controlling several other racks of plc's at other locations or even locally step seven is IO locations this is a little bit more about the remote IO basically okay will all of my IO fit in one rack well let's say that I fill up a 205 system and I need more inputs and outputs well I can buy another 205 rack put an expansion module in it and a Communications module for that and start adding more IO 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 rack 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 uh modules to do this if you need it and keep in mind the future expansion stuff if you know that sometime in the future you're going to expand more you know can I use remote iio do I have the right products 250 or 260 processor you can use expansion or remote IO either one okay expansion pretty much a plug and go the processor sees all of the io and uh 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 to look at distance of your racks how far apart are they going to be in the 205 expansion you can go up to 90 ft away if you need to go further than that well you're going to have to go to remote IO it's a little bit different you have to program for your inputs and outputs that are out at those slave racks um but you can go further distances if you need some real far distances you can look at uh uh we can get into fiber optic modules that are master and slave so fiber optic of course carries Communications a lot further remote IO 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 um 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 cond do it 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 uh 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 uh other outside devic devices we've got ethernet going to a switch going to other plcs so it's networked to these plc's it's going to a drive here we've got a high-speed uh counter going to some stuff we've got uh servos we've got uh break out of one ethernet Communications card and we're going to another computer and several HMI touch panels got barcode readers we've got uh scales all kinds of other hmis more drives maybe it's going back to a plant computer that's uh reading all kinds of information over the plant uh maybe this computer's outside of the plant so it's got to go through some type of communications as you can see here this is a modem a telephone modem or a modem so it's going through the MDM tell modem and uh talk into a computer so you need to make sure that you have all the right Communications this going to get a little complicated if you're not real familiar so you might have to get some outside help but have networking ethernet modbus is a big uh Universal communication device net proy buus and asky like I said asky stuff like barcodes okay step nine we're almost at the end here step nine 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 your laptop's great you 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 do you have laptops um held handheld programming all you need is a little handheld and it looks just like this picture here personally I'd Rather somebody 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 timec consuming trying to figure one out memory modules um let's just say for instance dd5 the little break unit you can buy this little d0 D1 MC which is a memory card or a memory slot um and you can pop it into 05 you can suck the program onto this little memory module and and then you can send it out to your customer an oem could do this you could send it out to your buddy and say hey got a new program on this memory module pop it in your 05 and run it so he can pop it in and either he can transfer that program into the memory of his uh 05 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 uh use the software or transfer with software or you just don't want them in there me messing with it you can send them this little memory module also so 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 card out and they can pop it in the processor and let it run off of it so easy way to JD 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 a PLC please follow us along to the uh third portion of this and uh we'll talk a little bit more about some examples break our plc's down and also give you some resources