Ron Beaufort
Lifetime Supporting Member
Greetings to all,
I got an interesting phone call the other night from our new friend Naeem in Lahore, Pakistan ... we met Naeem (roomi177) in this thread ... it seems that he wants to learn about Allen-Bradley PID control ... I agreed to help as much as I can – and as often as my schedule will allow ... and then right after we hung up I instantly thought of several questions that I should have asked him while we were on the phone ...
and so to Naeem:
question 1: why do you want to learn this material? ... I’ll assume (gosh I hate that word) that it’s because you hope to eventually profit financially from the knowledge ... and that’s an EXCELLENT reason – something that we can all identify with ... if you have any other reason, please let me know ... that might (or might not) change the way we proceed with this project ...
question 2: which Allen-Bradley platform do you want to concentrate on – at least in the beginning? ... there are four basic ones to choose from:
(1) the Allen-Bradley PLC-5 family
(2) the Allen-Bradley SLC-500 family
(3) the Allen-Bradley MicroLogix family
(4) the Allen-Bradley ControlLogix family
all of these families have at least some models that are capable of doing PID control ... here are some of the issues to consider in making your decision ...
(1) the Allen-Bradley PLC-5 family ... this technology has been around for about 20 years or so ... it’s a tried-and-proven family and (at least in my neighborhood) there are tons of this stuff still installed and reliably controlling right along ... steel mills and paper mills and other heavy industries feel more comfortable with the “solid” look and feel of this older equipment ... the bad news is that it’s expensive to buy brand new hardware for this larger and sturdier platform ... the good news is that it’s been around so long that a lot of the hardware is available used – and in some cases (joy of joys) you can occasionally find it actually being given away for free
... the biggest issue that you’ll face if you decide to use the PLC-5 platform will probably be in obtaining the PLC hardware and the software to program it ... the minimum hardware requirements to do realistic PID experiments will be a processor, a chassis, a power supply, an analog input module, and an analog output module ... make sure that the processor is an “enhanced” model ... specifically, do NOT buy a PLC-5/15 or a PLC-5/25 processor ... these are generally much cheaper ... but the only way to communicate with them for programming purposes is through a DH+ (Data Highway Plus) connection ... that connection alone will probably cost about $1,000 – even for “used” equipment ... on the other hand, if you stay with an enhanced processor, you can do all of your programming through the PLC’s built-in serial port with a cable that you can make yourself for about $5 ... secret handshake: the PLC-5/20 is an enhanced model ... so why is the higher numbered PLC-5/25 NOT an enhanced? ... no one knows ... but a PLC-5/20 or anything above a PLC-5/25 is probably ok ... the software that you’ll need for the PLC-5 family is RSLogix5 ... the cost is about $3,500 for a licensed legal copy ...
(2) the Allen-Bradley SLC-500 family ... this platform has been around for about 15 years or so ... the basic idea is that it’s supposed to do the same controlling functions as the larger PLC-5 family for approximately one-third the cost ... there are still lots of this stuff in use too ... if you’re going to choose this platform, I’d recommend that you get at least an SLC-5/03 processor or higher ... anything less than that will either not do PID at all – or its PID capabilities will be very limited ... the minimum hardware requirements to do realistic PID experiments will be a processor, a chassis, a power supply, an analog input module, and an analog output module ... but ... the SLC platform does have a “combination” type analog module available which provides both inputs and outputs in one unit ... if the extra money is available, I’d suggest an SLC-5/05 processor ... that model will provide built-in Ethernet capability and make it faster and easier to gather and log the real-time PID data on your programming computer ... the software that you’ll need for the SLC-500 family is RSLogix500 ... bigger number – but smaller price ... the cost is about $1,100 for a licensed legal copy ...
(3) the Allen-Bradley MicroLogix family ... even though some of these (but not all) are capable of doing PID control, I do not recommend that you start out learning the subject on this platform ... one big reason is that they don’t allow online programming ... so you’ll find yourself having to shut down the system over and over in order to make changes to the program ... the software is RSLogix500 (same as for the SLC-500 line) but this time you could get by with the “starter” version ... the cost is about $500 ... even though the MicroLogix might be the cheapest way to get into the Allen-Bradley PID game, I don’t recommend this path unless you’re only doing this PID thing for the mental challenge and personal satisfaction involved ... basic idea: a prospective employer is probably going to be “less-than-impressed” with your PID expertise if the only platform that you can brag about is the tiny MicroLogix ... steel mills and paper mills, etc. usually have little or no use for this platform – if for no other reason than the fact that they simply can’t afford to keep shutting down their manufacturing processes to make programming changes ...
(4) the Allen-Bradley ControlLogix family ... this is Allen-Bradley’s newest line ... eventually it will (so they say) completely replace the PLC-5 and the SLC-500 platforms ... (and I’ve been hearing that “kilometers and liters” are going to completely replace “miles and gallons” since I was in the fourth grade too – and I’m still waiting) ... but the ControlLogix is a solution (or some people would say a “problem”) that is definitely not going to go away ... here again, the minimum hardware requirements to do realistic PID experiments will be a processor, a chassis, a power supply, an analog input module, and an analog output module ... the list prices will GENERALLY be slightly more than for the SLC-500 – but less than the equivalent PLC-5 prices ... the software is RSLogix5000 ... it’s been awhile since I’ve seen a price on this one – but I think that it’s about $2,500 ...
so that’s the basic rundown on the various platforms ... right now you’ve got to be asking yourself: “so is learning PID on one platform all that different from learning on another?” ... yes, it is ... now “tuning the loop” is pretty much the same (but not exactly) from one platform to the other ... but the biggest issue will be in how to get the analog field signals into and out of the system ... the PLC-5 uses Block Transfer Reads and Writes to move the analog signals in and out ... the SLC-500 and ControlLogix platforms do not ... the PID instructions on the PLC-5 and the ControlLogix platforms offer many more choices and options that the smaller SLC-500 systems don’t even have available ... also the PID instruction’s inputs and outputs must be scaled to different ranges when working with the various types of processors ...
so ... which platform should you choose? ... I suggest that you make that decision based on what would likely be the most profitable path in the future ... specifically, if I were in your shoes, I’d start by asking around at some of the businesses where I might hope to eventually market my PID skills ... for example: I’d go to the paper mill, to the steel mill, to the chemical plants, to the cement plants, and to any other place where I thought (or hoped) that I might have some chance of working on Allen-Bradley PID control ... and I’d ask them what types of platforms they’re currently using – and what they plan to be using in the foreseeable future ... basic idea: whatever you learn about PID on one platform will certainly be of some amount of benefit on any other platform ... but ... if given a choice, why would you spend your time, money, and effort learning on the “wrong” platform? ...
continued in next post ...
I got an interesting phone call the other night from our new friend Naeem in Lahore, Pakistan ... we met Naeem (roomi177) in this thread ... it seems that he wants to learn about Allen-Bradley PID control ... I agreed to help as much as I can – and as often as my schedule will allow ... and then right after we hung up I instantly thought of several questions that I should have asked him while we were on the phone ...
and so to Naeem:
question 1: why do you want to learn this material? ... I’ll assume (gosh I hate that word) that it’s because you hope to eventually profit financially from the knowledge ... and that’s an EXCELLENT reason – something that we can all identify with ... if you have any other reason, please let me know ... that might (or might not) change the way we proceed with this project ...
question 2: which Allen-Bradley platform do you want to concentrate on – at least in the beginning? ... there are four basic ones to choose from:
(1) the Allen-Bradley PLC-5 family
(2) the Allen-Bradley SLC-500 family
(3) the Allen-Bradley MicroLogix family
(4) the Allen-Bradley ControlLogix family
all of these families have at least some models that are capable of doing PID control ... here are some of the issues to consider in making your decision ...
(1) the Allen-Bradley PLC-5 family ... this technology has been around for about 20 years or so ... it’s a tried-and-proven family and (at least in my neighborhood) there are tons of this stuff still installed and reliably controlling right along ... steel mills and paper mills and other heavy industries feel more comfortable with the “solid” look and feel of this older equipment ... the bad news is that it’s expensive to buy brand new hardware for this larger and sturdier platform ... the good news is that it’s been around so long that a lot of the hardware is available used – and in some cases (joy of joys) you can occasionally find it actually being given away for free
... the biggest issue that you’ll face if you decide to use the PLC-5 platform will probably be in obtaining the PLC hardware and the software to program it ... the minimum hardware requirements to do realistic PID experiments will be a processor, a chassis, a power supply, an analog input module, and an analog output module ... make sure that the processor is an “enhanced” model ... specifically, do NOT buy a PLC-5/15 or a PLC-5/25 processor ... these are generally much cheaper ... but the only way to communicate with them for programming purposes is through a DH+ (Data Highway Plus) connection ... that connection alone will probably cost about $1,000 – even for “used” equipment ... on the other hand, if you stay with an enhanced processor, you can do all of your programming through the PLC’s built-in serial port with a cable that you can make yourself for about $5 ... secret handshake: the PLC-5/20 is an enhanced model ... so why is the higher numbered PLC-5/25 NOT an enhanced? ... no one knows ... but a PLC-5/20 or anything above a PLC-5/25 is probably ok ... the software that you’ll need for the PLC-5 family is RSLogix5 ... the cost is about $3,500 for a licensed legal copy ...
(2) the Allen-Bradley SLC-500 family ... this platform has been around for about 15 years or so ... the basic idea is that it’s supposed to do the same controlling functions as the larger PLC-5 family for approximately one-third the cost ... there are still lots of this stuff in use too ... if you’re going to choose this platform, I’d recommend that you get at least an SLC-5/03 processor or higher ... anything less than that will either not do PID at all – or its PID capabilities will be very limited ... the minimum hardware requirements to do realistic PID experiments will be a processor, a chassis, a power supply, an analog input module, and an analog output module ... but ... the SLC platform does have a “combination” type analog module available which provides both inputs and outputs in one unit ... if the extra money is available, I’d suggest an SLC-5/05 processor ... that model will provide built-in Ethernet capability and make it faster and easier to gather and log the real-time PID data on your programming computer ... the software that you’ll need for the SLC-500 family is RSLogix500 ... bigger number – but smaller price ... the cost is about $1,100 for a licensed legal copy ...
(3) the Allen-Bradley MicroLogix family ... even though some of these (but not all) are capable of doing PID control, I do not recommend that you start out learning the subject on this platform ... one big reason is that they don’t allow online programming ... so you’ll find yourself having to shut down the system over and over in order to make changes to the program ... the software is RSLogix500 (same as for the SLC-500 line) but this time you could get by with the “starter” version ... the cost is about $500 ... even though the MicroLogix might be the cheapest way to get into the Allen-Bradley PID game, I don’t recommend this path unless you’re only doing this PID thing for the mental challenge and personal satisfaction involved ... basic idea: a prospective employer is probably going to be “less-than-impressed” with your PID expertise if the only platform that you can brag about is the tiny MicroLogix ... steel mills and paper mills, etc. usually have little or no use for this platform – if for no other reason than the fact that they simply can’t afford to keep shutting down their manufacturing processes to make programming changes ...
(4) the Allen-Bradley ControlLogix family ... this is Allen-Bradley’s newest line ... eventually it will (so they say) completely replace the PLC-5 and the SLC-500 platforms ... (and I’ve been hearing that “kilometers and liters” are going to completely replace “miles and gallons” since I was in the fourth grade too – and I’m still waiting) ... but the ControlLogix is a solution (or some people would say a “problem”) that is definitely not going to go away ... here again, the minimum hardware requirements to do realistic PID experiments will be a processor, a chassis, a power supply, an analog input module, and an analog output module ... the list prices will GENERALLY be slightly more than for the SLC-500 – but less than the equivalent PLC-5 prices ... the software is RSLogix5000 ... it’s been awhile since I’ve seen a price on this one – but I think that it’s about $2,500 ...
so that’s the basic rundown on the various platforms ... right now you’ve got to be asking yourself: “so is learning PID on one platform all that different from learning on another?” ... yes, it is ... now “tuning the loop” is pretty much the same (but not exactly) from one platform to the other ... but the biggest issue will be in how to get the analog field signals into and out of the system ... the PLC-5 uses Block Transfer Reads and Writes to move the analog signals in and out ... the SLC-500 and ControlLogix platforms do not ... the PID instructions on the PLC-5 and the ControlLogix platforms offer many more choices and options that the smaller SLC-500 systems don’t even have available ... also the PID instruction’s inputs and outputs must be scaled to different ranges when working with the various types of processors ...
so ... which platform should you choose? ... I suggest that you make that decision based on what would likely be the most profitable path in the future ... specifically, if I were in your shoes, I’d start by asking around at some of the businesses where I might hope to eventually market my PID skills ... for example: I’d go to the paper mill, to the steel mill, to the chemical plants, to the cement plants, and to any other place where I thought (or hoped) that I might have some chance of working on Allen-Bradley PID control ... and I’d ask them what types of platforms they’re currently using – and what they plan to be using in the foreseeable future ... basic idea: whatever you learn about PID on one platform will certainly be of some amount of benefit on any other platform ... but ... if given a choice, why would you spend your time, money, and effort learning on the “wrong” platform? ...
continued in next post ...