Page 161 - Programmable Logic Controllers, Fifth Edition

Input Ladder logic program Outputs
L1 SW L2
TOF
Switch TIMER OFF DELAY EN
SW Timer T4:1 OL
Preset 5 DN M1
Accumulated 0
OL
TOF
TIMER OFF DELAY EN M2
Timer T4:2
Preset 10 DN OL
Accumulated 0 M3

TOF
TIMER OFF DELAY EN
Timer T4:3
Preset 15 DN
Accumulated 0
T4:1/DN M1

T4:2/DN M2

T4:3/DN M3

Figure 7-22 Program for switching motors off at 5 s intervals.

• Timer T4:2 times out 5 s later resetting its done bit • When limit switch LS1 is opened, the off-delay
to zero to de-energize motor M2. timer coil TD de-energizes and the time-delay
• Timer T4:3 times out 5 s later resetting its done bit period is started.
to zero to de-energize motor M3.
L1 L2
Figure 7-23 shows a hardwired off-delay timer relay
circuit with both instantaneous and timed contacts. The LS1
operation of the circuit can be summarized as follows: 5 s TD
• When power is first applied (limit switch LS open), TD-1 OL
motor starter coil M1 is energized and the green M1
pilot light is on.
• At the same time, motor starter coil M2 is de- TD-2 OL
energized, and the red pilot light is off. M2
• When limit switch LS closes, off-delay timer coil
TD energizes. TD-3
• As a result, timed contact TD-1 opens to de- G
energize motor starter coil M1, timed contact TD-2
closes to energize motor starter coil M2, instanta- TD-4
neous contact TD-3 opens to switch the green light R
off, and instantaneous contact TD-4 closes to switch
the red light on. The circuit remains in this state as Figure 7-23 Hardwired off-delay timer relay circuit with
long as limit switch LS1 is closed. both instantaneous and timed contacts.

142 Chapter 7 Programming Timers

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