Page 237 - Programmable Logic Controllers, Fifth Edition - Mobile version

Ladder logic program
Ladder logic program
LES Output L2 LEQ PL1 Output L2
LESS THAN (A<B) PL1 LESS THAN OR EQUAL
Source A PL1 (A B) PL1
C5:10.ACC Source A
Source B C5:1.ACC
350 Source B
457
Figure 10-24 LES logic rung.
Figure 10-26 LEQ logic rung.

example of a GRT logic rung. The operation of the rung
can be summarized as follows: • The value stored at source B is 23.
• Therefore the output will be true or on.
• The instruction is either true or false, depending on
the values being compared. The less than or equal (LEQ) instruction is an input
• When the accumulated value of timer T4:10, stored instruction that compares source A to source B: when
at the address of source A, is greater than the con- source A is less than or equal to source B, the instruction
stant 200 of source B, the output will be on; other- is logically true; otherwise it is logically false. Figure 10-26
wise the output will be off. shows an example of an LEQ logic rung. The operation of
the rung can be summarized as follows:
The less than (LES) instruction is an input instruction that
compares source A to source B: when source A is less than • When the accumulated count of counter C5:1 is less
source B, the instruction is logically true; otherwise it is logi- than or equal to 457, the pilot light will turn on.
cally false. Figure 10-24 shows an example of an LES logic • The accumulated value of the counter is less than 457.
rung. The operation of the rung can be summarized as follows: • Therefore the output will be false or off.

• The instruction is either true or false, depending on Figure 10-27 shows an example of an up-counter used
the values being compared. in conjunction with the LES, EQU, and GRT compare
• When the accumulated value of counter C5:10, instructions to trigger outputs based on different values
stored at the address of source A, is less than the of the counter’s accumulated count. The operation of the
constant 350 of source B, the output will be on; program can be summarized as follows:
otherwise, it will be off. • A Less Than (LES) 10 comparison is made with the
The greater than or equal (GEQ) instruction is an counter’s accumulative value. As a result, the LESS
input instruction that compares source A to source B: Output will be energized anytime the accumulated
when source A is greater than or equal to source B, the count is 9 or less.
instruction is logically true; otherwise it is logically false. • An Equal (EQU) to 20 comparison is made with the
Figure 10-25 shows an example of a GEQ logic rung. The counter’s accumulative value. As a result, the EQU
operation of the rung can be summarized as follows: Output will be energized only when the accumu-
• When the value stored at the address of source A, lated count is 20.
N7:55, is greater than or equal to the value stored at • A Greater Than (GRT) 30 comparison is made with
the address of source B, N7:12, the output will be the counter’s accumulative value. As a result, the
true; otherwise, it will be false. GRT Output will be energized anytime the accumu-
• The value stored at source A is 100. lated count is 31 or more.
The limit test (LIM) instruction is used to test whether
values are within or outside the specified range. Applica-
Ladder logic program Output
GEQ L2 tions in which the limit test instruction is used include
GREATER THAN OR EQUAL PL1 allowing a process to operate as long as the temperature is
(A B) within or outside a specified range.
Source A N7:55 PL1 Programming the LIM instruction consists of entering
100
three parameters: low limit, test, and high limit. The limit
Source B N7:12 test instruction functions in the following two ways:
23
• The instruction is true if—The lower limit is
Figure 10-25 GEQ logic rung. equal to or less than the higher limit, and the test

218 Chapter 10 Data Manipulation Instructions

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