There are many different signals in use today, but fewer than there were ten years ago. The most important thing to remember is to make sure that your I/O module matches the actual signal / device that you are connecting to.
Types of I/O
Typically there are three types of I/O:
- Digital I/O 2. Analogue I/O 3. Specialty I/O
Discrete(digital) I/O is simply On / Off, True / False or some other binary designation of two states. Analogue I/O’s are varying levels such as temperatures, pressures, levels. Specialty I/O is everything else — high speed motion control, high speed counters, high speed interfaces to encoders, etc. Note the word “high speed” in connection with specialty I/O. Typically a specialty I/O module is a module with its own processor that allows the module to operate faster than the PLC and regular I/O.