Boiler Blowdown via Micrologix1100 with Analog I/O Expansion

I currently need some assistance for a PLC project that I have. Currently I am taking a PLC course that hasn't been very fruitful, but have found more information for many of my questions so far amongst the numerous posts. My PLC knowledge is limited, but growing with each new post, YouTube video, etc. that I have encountered. Not so much with the class. It is the instructor's first time teaching it and my first time learning it.
I have to control the conductivity level of a boiler system by means of a temperature and conductivity probe. Those are the two control variables. My process variables are two motor actuated valves.
I am using a Micrologix 1100 1763-L16DWD with 1762-IF20F2 analog I/O expansion card. The temperature probe sends out a 4-20mA signal and the conductivity probe also sends out a 4-20mA signal. I have already discovered the switch settings by using the manual and this forum. The output goes to two motor actuated valves that are controlled by 4-20mA each.
In class we use a PLC-5/20E with simulator card (8 switches and 8 LED outputs), which originally confused me between the differences. After much trial and error I discovered that I only had to go to the word level addressing for the Micrologix 1100.
My current speed bump is finding more information concerning the implementation of a PID block. I want to use proportional control to start, but would like to see how PI may work. I have read through the forums to not preface the PID control with ANYTHING. I created a state diagram and sequence of operations that should take place. In order to have periodic blowdown take place, I want to use a timer. But, I was thinking about using the DONE bit of a TIMER, prefacing the PID block, but avoided it after research.
On the same token, it seems as though I can run a subroutine for the PID. The catch is that we are no where near subroutines in my class. Quite a bit of my learning has been outside of my class. If I created a subroutine for a PID block, can I also do one for my SCP's? I have some questions about SCP's as well, but I had a jumpstart with this forum and YouTube.

Questions:
Can I have some wisdom in regards to PID blocks, SCP's, and running them in subroutines? Base example for me to trial and error implementation?

Thank you.

SCP can be run in a subroutine before using it in PID. acdg to help

Input - Enter a value(in this case the analog input) to be scaled. This can be a word address or an address of floating point data elements.

Input Min - Enter a minimum value for the input (low end of range). This value can be a word address, a long (double-word) address, an integer constant, floating point data element, or a floating point constant.

Input Max - Enter a maximum value for the input (high end of range). This value can be a word address, a long (double-word) address, an integer constant, floating point data element, or a floating point constant.

Scaled Min - Enter a minimum scaling value representing the low end of the range to which you want to scale the input. The scaling relationship is linear. The value can be a word address, a long (double-word) address, an integer constant, floating point data element, or a floating point constant.

Scaled Max - Enter a maximum scaling value representing the high end of the range to which you want to scale the input. The scaling relationship is linear. The value can be a word address, a long (double-word) address, an integer constant, floating point data element, or a floating point constant.

Output - Enter an address for the scaled value that is returned after the instruction is executed. This value can be a word address, a long (double-word) address or an address of floating point data elements. If any floating-point file types or floating-point constants are encountered in the above parameters, then the entire instruction is treated as floating point, and all immediate integer data values are converted to immediate floating-point data values.

Note: The input minimum, input maximum, scaled minimum, and scaled maximum are used to determine the slope and offset values. The input value can go outside of the specified input limits and no ordering is required. For example, the scaled output value will not necessarily be clamped between the scaled minimum and scaled maximum values.

Click to expand...

yep, in PID it is trial and error.