Page 195 - Programmable Logic Controllers, Fifth Edition - Mobile version

In this process, conveyor M1 is used to stack metal plates
onto conveyor M2. The photoelectric sensor provides an • After conveyor M2 has been operated for 5 s, it
stops and the sequence is repeated automatically.
input pulse to the PLC counter each time a metal plate • The done bit of the timer resets the timer and the
drops from conveyor M1 to M2. When 15 plates have counter and provides a momentary pulse to auto-
been stacked, conveyor M2 is activated for 5 s by the PLC matically restart conveyor M1.
timer. The operation of the program can be summarized
as follows: Figure 8-35 shows a motor lock-out program. This pro-
gram is designed to prevent a machine operator from starting
• When the start button is pressed, conveyor M1 a motor that has tripped off more than 5 times in an hour.
begins running. The operation of the program can be summarized as follows:
• After 15 plates have been stacked, conveyor M1 • The normally open overload (OL) relay contact momen-
stops and conveyor M2 begins running. tarily closes each time an overload current is sensed.

Ladder logic program

Inputs Start Stop OL Lock-out Motor Outputs
L1 T4:0 light L2

EN
Stop Motor
Motor

Start OL T4:0 5 min Lock-out
TON light
TIMER ON DELAY EN
DN Timer T4:0 DN
Time base 1
OL T4:0
Preset 300
Accumulated 0
EN
Reset 1 hr
PB T4:1 TON
TIMER ON DELAY EN
Timer T4:1
DN DN
Time base 1
Preset 3600
Accumulated 0
OL
CTU
COUNT-UP COUNTER CU
OL relay Counter C5:0
Preset 6 DN
Accumulated 0
T4:1 C5:0
RES
DN
Reset-PB

Lock-out
C5:0 light
L
DN
Lock-out
L
Reset-PB light
U

Figure 8-35 Motor lock-out program.
Source: This material and associated copyrights are proprietary to, and used with the permission of Schneider Electric.

176 Chapter 8 Programming Counters

pet73842_ch08_156-183.indd 176 03/11/15 3:58 PM