Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations User Manual
Page 39
Fundamental Instruction Set
Chapter 5
5Ć2
Perhaps an example might make this more clear:
C1
C3
A
True
True
True
C2
Here, a series of conditions, (C1, C2, C3) must be true before an action is
performed.
C1 =
Input switch 1. When the switch is on, this condition is
true. This switch turns on a conveyer belt.
C2 =
Input sensor 1. When the sensor is off, this condition is
true. This sensor detects if the temperature in the
factory is below 40oC.
C3 =
Input sensor 2. When the sensor is on, this condition is
true. This sensor detects the presence of a part of the
conveyer belt.
A =
The part will be drilled
_ =
The path of conditions is continuous, that is, all
conditions are true.
When C1, C2, and C3 are true, then a continuous path is made to a particular
action. In this case, the continuous path causes the part to be drilled.
When the path of conditions is continuous, we say that the rung is true. When
the path of conditions is not continuous, we say the rung is false.
C1
C2
C3
A
True
False
True
Here the path of conditions is not continuous because condition 2 is false.
Therefore, the action is not performed. We say the rung is false.
Recall that input and output devices are connected, via field wiring, to the
controller’s input and output terminals. Furthermore, each of these terminals
correspond to a memory bit that reflects the state of that device.
As a review, if the device goes on, then we say the corresponding bit in memory
is set to a 1. If the device goes off, we say the corresponding bit in memory is
Hardware Review
Set vs. Reset