Assigning Numbers To Timers And Counters; Step 3-Writing A Relay Ladder Diagram - Omron SYSMAC C Series User Manual

Introduction to programming
Step 3
Writing a relay ladder
diagram
(1)
0000 0001 (soo)
0002
0003 0004
(2)
0000 0001
y
0000 0004
0002
0003 0001
H
0002
0003 0004
—
Assigning numbers to timers and counters
The C20 can accommodate up to 48 timers or 48 counters, or
combinations of timers and counters not exceeding 48. How these are
used is explained in Chapter 4. They must also be assigned identifying
numbers, in a range from 00 to 47. (Note that these are not input/output
points, but rather a way for you to identify the timer or counter you want to
use.)
There are two basic considerations when assigning counter and timer
numbers.
Do not give counters and timers the same number. For instance, there
cannot be a Timer 01 and a Counter 01.
When you're finished assigning the input and output points, internal
auxiliary relays, and timers/counters, you're ready to proceed to the next
step.
So far we know three basic things about our operation. We know which
devices are to be controlled, we know how they relate to each other, and
we know the sequence (or timing) at which the controlled tasks must take
place.
Now we need to put this down in a form that is codeable—that is, in the
form of a relay ladder diagram.
For this you'll use the four-digit numbers you just assigned to the input
and output relays and internal auxiliary relays, as well as the two-digit
numbers you gave to the timers and counters. You'll also use such relay
symbols as the following. The complete list of symbols is shown in
Appendix B.
Hi Ah -0O
Normally open contact Normally closed contact Output
In writing the ladder diagram, keep these things in mind.
Each logic line starting from the left bus bar must end with a relay coil, a
timer/counter, or a special instruction. Unlike the actual circuit diagram,
the right bus bar need not be written into the ladder diagram.
The number of contacts in series or paraltel is not limited for use on a logic
line within the programming capacity of the PC. Therefore, you can use as
many contacts as you wish. If this feature of the C20 is effectively used,
even a complicated circuit can frequently be replaced with a simpler one.
The bridge circuit (1) shown on the left, for example, could be replaced
with the one shown below it (2).