Page 162 - Programmable Logic Controllers, Fifth Edition

Input
LS1 Ladder logic program Outputs Figure 7-24 Equivalent
PLC program of the hardwired
L1 TOF L2 off-delay timer relay circuit
TIMER OFF DELAY EN OL
Timer T4:1 containing both instantaneous
LS1 Time base 1.0 M1 and timed contacts.
Preset 5 DN
Accumulated 0 OL
M2
T4:/DN M1
G G
T4:/DN M2

R R
T4:/EN G

T4:/EN R

• Instantaneous contact TD-3 closes to switch the Figure 7-24 shows an equivalent PLC program of the
green light on, and instantaneous contact TD-4 hardwired off-delay timer relay circuit containing both
opens to switch the red light off. instantaneous and timed contacts. The timer instruction
• After a 5-s time-delay period, timed contact TD-1 carries out all of the functions of the original physical timer.
closes to energize motor starter M1, and timed con- Figure 7-25 shows a program that uses both the on-
tact TD-2 opens to de-energize motor starter M2. delay and the off-delay timer instruction. The process

PS1 PS2 PS3

Tank Tank
A B
Pump

Ladder logic program

Stop Start T4:5 PS1 Pump

Inputs Output
L1 Pump DN L2

Stop Pump TON Pump delay OL
TIMER ON DELAY EN Pump M
Start Timer T4:6
Time base 1.0 DN
Preset 5
PS1 Accumulated 0
T4:6 PS2 Pump time
TOF
TIMER OFF DELAY EN
PS2 DN Timer T4:5
PS3 Time base 1.0 DN
Preset 14
Accumulated 0
PS3

Figure 7-25 Fluid pumping process.

Programming Timers Chapter 7 143

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