Schematics text descriptions I use upper - lower case just like I would write any other text.
The font size must not be too small !
I use upper caps to highlight something important. I.e. "Oil pressure is ok" vs. "oil pressure is NOT ok".
All upper case
texts are more difficult to read, at least to me.
Component tags are defined by certain standards, and are always in upper case.
Component tags are identical in the schematics and in the PLC program.
PLC addresses follows certain standards, and are always in upper case, i.e. "I 0.5", "Q 2.2". I prefer to use a space to separate the address type and the address number.
PLC addresses are identical in the schematics and in the PLC program.
edit:
When writing program in structured text for example, reserved keywords are all caps but variables are written in the 'natural' way, but with underscores instead of spaces.
I.e. IF Condition_high THEN Alarm_high := TRUE ;
This is where you can have some really heated debates as to what is 'right'.
I’m not sure who arbitrarily decided all caps is harder to read but times do change.
Have you ever seen a book, newspaper or magazine printed in all caps only ?
The question should be, why did someone decide that all caps is the standard for texts in the computer world ?