using rslogix micro. When to add modules?

[Jrivers010]

under rslogix and IO configurations, you use that to add modules for digital and analog. and for various types of those modules, such as thermocouple input module, or a normal Analog 4 Chan. input.

however, how do you know when you need to add this? How can i look it up if the program i am about to code requires a module or not?

also, on one of the online courses, the instructor added a "analog 4 chan. input" module when showing analog example. but he didnt add any other output module, even tho he used SCP instruction. (and in general, if u have an input, isnt there an output? so you would need an output module anyhow. so how come he didnt add it in?)

 

[rdrast]

#1) You should know what IO you need long before you start programming an application. Typically, this is even pretty closely estimated during a quote process, as it affects the quote.
See how many inputs and outputs are needed by the application, and of what type, based on the other devices, the application requirements, the schematics, etc. and add them to the program first.
That is one of the things an engineer does.

#2) No, you do not need an output just because you have an input. In 90% or more of the cases, any type of scaling done to an analog input (SCP included) is done for convenience of the programmer, or as information displayed to an operator. 0-100% for example is much clearer than say 3277 to 16383 (example raw value of a 4-20 mA input module).

For analogs, there are typically more inputs than outputs on real systems, as they convey information about how a process is running, bur aren't necessarily used as a control element.

 

[AutoMax]

Well, you should probably know what the program you're going to write is intended to accomplish and have an idea how you're going to accomplish it. If you were writing a program to run a motor you would probably have some inputs to start and stop it and some kind of outputs to actually start the motor.
Your instructor was probably trying to explain the SCP instruction without muddying the waters with additional logic.

 

[Jrivers010]

@everyone ah sorry, i shouldve been mroe clear on my question. I meant, how do you know whehter you need to add a 4 input channel analog or not? NOT because you dont check your program you are about to write on how many io it'll have, but because I dont know how many the PLC processor has.

#2) No, you do not need an output just because you have an input. In 90% or more of the cases, any type of scaling done to an analog input (SCP included) is done for convenience of the programmer, or as information displayed to an operator. 0-100% for example is much clearer than say 3277 to 16383 (example raw value of a 4-20 mA input module).

wait, so using a SCP to display an input number to a scaled value ISNT an output? im confused more now on what i thought i knew lol

For analogs, there are typically more inputs than outputs on real systems, as they convey information about how a process is running, bur aren't necessarily used as a control element.

What does it mean about "control elements" ? is it the logic, the io, or SCP type stuff? (sorry i am self learning so i dont have textbook definitions down)

 

[AutoMax]

@everyone ah sorry, i shouldve been mroe clear on my question. I meant, how do you know whehter you need to add a 4 input channel analog or not? NOT because you dont check your program you are about to write on how many io it'll have, but because I dont know how many the PLC processor has.

You determine it in the same manner as discrete I/O.

wait, so using a SCP to display an input number to a scaled value ISNT an output? im confused more now on what i thought i knew lol

Personally, I consider tags tied to HMI displays outputs, but that's a matter of semantics. I'll drop the subject so the thread doesn't go off the rails.

What does it mean about "control elements" ? is it the logic, the io, or SCP type stuff? (sorry i am self learning so i dont have textbook definitions down)

You might use an analog input scaled to a display for simple information. Think of the difference between a thermometer and a thermostat. One device simply provides information, the other acts on the information.

 

[Jrivers010]

You determine it in the same manner as discrete I/O.

sorry. im not quite sure what you mean by this. But basically, while i am doing Udemy PLC 2 course by paul lynn (currently finished project 2) I just go right ahead and program, adding my inputs and outputs. once i finish and go to emulate, it works. So i guess all the I/O program files i used (i.e. ... I:0/0 or O:0/3 etc) with my default micrologix 1100 processor had the input/output module.

but how would i KNOW that beforehand?

You might use an analog input scaled to a display for simple information. Think of the difference between a thermometer and a thermostat. One device simply provides information, the other acts on the information.

oh that actually makes alot of sense. so the SCP is a DISPLAY (like the thermometer giving the temperature of the medium) and NOT an output? so if i was programming a simple thermometer, i would only need 1 analog input? but if i was going to use that display it gives out, to control something, say a boiler, it would need 1 analog input PLUS 1 analog output? (keeping it a simple process for clarity. im sure there are more connections between the input of thermometer to the boiler.)

 

[Jrivers010]

0-100% for example is much clearer than say 3277 to 16383 (example raw value of a 4-20 mA input module).

i thought for raw value/proportional, it was 4000-20000?? and 0 - 16383 for scaled for PID ?

 

[AutoMax]

sorry. im not quite sure what you mean by this. But basically, while i am doing Udemy PLC 2 course by paul lynn (currently finished project 2) I just go right ahead and program, adding my inputs and outputs. once i finish and go to emulate, it works. So i guess all the I/O program files i used (i.e. ... I:0/0 or O:0/3 etc) with my default micrologix 1100 processor had the input/output module.

but how would i KNOW that beforehand?

OK, so you're asking what on-board I/O your processor has from the manufacturer? RTFM

oh that actually makes alot of sense. so the SCP is a DISPLAY (like the thermometer giving the temperature of the medium) and NOT an output? so if i was programming a simple thermometer, i would only need 1 analog input? but if i was going to use that display it gives out, to control something, say a boiler, it would need 1 analog input PLUS 1 analog output? (keeping it a simple process for clarity. im sure there are more connections between the input of thermometer to the boiler.)

You're catching on, but you wouldn't necessarily need an analog output. An old fashioned thermostat in your house just close a pair of contacts, essentially the equivalent of a discrete (binary, zero or one, on or off) output.

EDIT- Output from the controller (thermostat) perspective. It would be an input to the furnace.

 

[Jrivers010]

OK, so you're asking what on-board I/O your processor has from the manufacturer? RTFM




You're catching on, but you wouldn't necessarily need an analog output. An old fashioned thermostat in your house just close a pair of contacts, essentially the equivalent of a discrete (binary, zero or one, on or off) output.

EDIT- Output from the controller (thermostat) perspective. It would be an input to the furnace.

oh right.. duh.. lol. will the manual also tell you what the resolution bit a PLC processor has? I previously thought every plc was a 14 bit resolution, but that seems to not be the case.

 

[AutoMax]

oh right.. duh.. lol. will the manual also tell you what the resolution bit a PLC processor has? I previously thought every plc was a 14 bit resolution, but that seems to not be the case.

I heartily recommend you spend a bit of time familiarizing yourself with the Rockwell Automation website. It's probably the best in the industry (that doesn't mean it's perfect, but even the Siemens advocates have to admit the Siemens site is atrocious.) The organization is very consistent, as is the manner documentation is presented. With just a bit of looking you will probably discover you don't actually have to RTFM in this instance, you can get a controller family comparison sheet that will answer questions about on-board I/O (quantity, type, resolution of analog, max frequency of high speed counters, etc.)

But still, RTFM. It's just the right way to go.

 

[rdrast]

Personally, I consider tags tied to HMI displays outputs, but that's a matter of semantics. I'll drop the subject so the thread doesn't go off the rails.

I disagree. HMI displays are values. Outputs are physical devices.

i thought for raw value/proportional, it was 4000-20000?? and 0 - 16383 for scaled for PID ?

Raw values can be anything, depending on the IO module. 0-20000, 9824 to 28422, -32768 to 32767, 1.000 to 5.000.
Not all modules are the same.