Step 1-Assessing The Controlled Operation; Input/Output Requirements; Sequence, Timing, And Relationship Assessment - Omron SYSMAC C Series User Manual

Introduction to programming
Step 1
Assessing the controlled
operation
This, of course, is a highly important part of setting up a PC-controlled
system. The PC's flexibility allows a wide latitude in not just what
operations can be controlled, but in how they will be controlled.
To apply a PC to any control task, the system requirements must first be
determined. The major part of that assessment focuses on the input/
output requirements.
Input/output requirements
The first thing that must be assessed is the number of I/Os that your
system will require. This is done by identifying each device that is to send
an input signal to the PC or which is to receive a PC output signal.
These should be totaled and it should be remembered that the C20, when
not expanded, has 16 input and 12 output points.
In terms of voltages, all the signals to the C20 must be 24 V DC inputs.
Because the programmable controller has three independent output
blocks, three output voltages are available through the common
terminals: 24 V DC and up to 250 V AC max.
Sequence, timing, and relationship assessment
Next you need to determine the sequence and timing at which these
controls will occur. How each of the controlled devices relates to the
others should be identified (such as a photoelectric switch to a motor), as
well as what response should occur between them.
For instance, a photoelectric switch might be functionally tied to a motor
by way of a counter within the PC. The motor would start when the PC
receives an input from a switch and would be stopped by the signal
output by the PC when the counter had received five input signals from
the photoelectric switch.
Each of the related tasks would be similarly determined from the
beginning of the controlled operation to the end.
Having made this assessment, you now will be ready to go to Step 2 of
programming—assigning the input/output devices or points.