134 Programmable Logic Controllers: Hardware and Programming
To specify the number of copies of the project files you want the
program to keep, enter the desired number in the
Number of Backups
text box that is located in the
Program Backup
section. Specify that
you want the system to keep only one copy of the project. This copy is
called the backup file.
6.12 Using the LogixPro Simulator to Create
Ladder Logic Diagrams
Example 6-1
The diagram in Figure 6-38 shows the use of normally open (NO)
and normally closed (NC) switches. As in relay ladder diagrams,
Switch-1 is open, and Switch-2 is closed. Closing the normally open
(NO) Switch-1 at address I:1/0 turns on the red pilot light (R-PLT) at
address O:2/0. Opening the normally closed (NC) Switch-2 at address
I:1/1 turns off the red pilot light.
Example 6-2
PLCs have the capability to lock their outputs in position. In
Figure 6-39, pressing pushbutton #1 (PB-1) turns on the pilot light at
address O:2/0. Once turned on, the pilot light locks itself in position
by closing its associated contact (O:2/0) in parallel with PB-1. Pressing
pushbutton #2 (PB-2) breaks the “lock-in-position” pass and turns off
the pilot light.
Normally Open (NO) and Normally Closed (NC) Switches.
000
001
O:2/0 I:1/0
End
Switch-1 Switch-2 R-PLT
I:1/1
Figure 6-38. PLC ladder logic diagram for Example 6-1. Normally open (NO) and normally closed
(NC) switches.