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Solenoid actuated when:(i) ON signal from number-pad outside door(ii) ON signal from door-open switch inside door Legend:
I:0/1 Number Pad Signal to open door
I:0/2 Push Button signal to open door
O:0/1 Solenoid to unlock door
O:0/1
T4: 1I:0/1 O:0/1
I:0/2DN
O:0/1
Preset:
Accum:
Base:
ENTimer: T4: 1
0.01
5000
DN
While O:0/1 remains ON,
Timer COUNTS DOWN from PRESET
COUNT DOWN = 0 ( T4:1) set to ON
Ladder Logic: Timers
Solenoid actuated door-lock
Solenoid ON for 5 sec, then OFF
Solenoid ON Door unlocked
Solenoid actuated when:(i) ON signal from number-pad outside door(ii) ON signal from door-open switch inside door
Legend:
I:0/1 Number Pad Signal to open door
I:0/2 Push Button signal to open door
O:0/1 Solenoid to unlock door
O:0/1
T4: 1I:0/1 O:0/1
I:0/2DN
O:0/1
Preset:
Accum:
Base:
ENTimer: T4: 1
0.01
5000
DN
Ladder Logic: Timers -- reset
Solenoid ON for 5 sec, then OFF
Solenoid actuated when:(i) ON signal from number pad outside door(ii) ON signal from door-open switch inside door
During ON, if button is pressed,Timer resets to PRESET
During ON, light indicator is ON
Legend:
I:0/1 Number Pad Signal to open door
I:0/2 Push Button signal to open door
O:0/1 Solenoid to unlock door
O:0/1
T4: 1I:0/1 O:0/1
I:0/2DN
O:0/1
Preset:
Accum:
Base:
ENTimer: T4: 1
0.01
5000
DN
O:0/1 O:0/2
T4: 1I:0/2
RESET
O:0/2 ‘Door Unlocked’ Light Indicator
LEGEND:I:0/1 door-openI:O/2 card-reader
O:0/1 solenoidO:0/2 light indicator
Ladder Logic: counters
Count the number of occurrences of an event
Pallet loading in factoryAfter 10 parts arrive on conveyor, worker comes to load pallet
Examples:
Pneumatic press hammerHit the part 20 times, then wait for part to be unloaded
Rice cooker alarmBeep 5 times when rice is cooked
EVENT: switch goes from OFF ON
Ladder Logic: counters
Pallet loading in factory After 4 parts arrive on conveyor:
STOP conveyor beltturn ON the indicator light
Legend:
I:0/1 Photo switch
I:0/2 Operator controlled Push Button to restart conveyor
O:0/1 Conveyor belt
O:0/2 Light Indicator
I:0/0 Conveyor ON
I:0/1
CU
DN
C5:1 O:0/2
C5: 1I:0/2
RESET
Preset:
Accum:
Count Up
C5: 1
4
0
Counter:
DN
O:0/1O:0/2I:0/0
Ladder Logic: car wash
Car arrives limit switch ON
Limit switch ON Washer ON
Washer ON:(i) Soapy water SPRAY ON (30 secs)(ii) Rinse: clean water SPRAY ON (30 secs)(iii) Automatic scrubber brushes car (15 secs)(iv) After washing 50 cars, the scrubber brush Auto-change
I:0/1 I:0/2 B1
O:0/0B1 T4:0 T4:1 T4:2
O:0/1B1
O:0/2B1
O:0/3
B1
B1
B1
I:0/1 : System On I:0/2 : Emergency Stop I:0/3 : Limit Switch
O:0/0 : Soap Water On O:0/1 : Rinse On O:0/2 : Scrubber On O:0/3 : Activate Scrubber Change
Notice how B1 and the timer outputs are used to control the logic according to the required timing.
O:0/2
Preset:Accum:
T4: 1
60000
Base: 0.01
Preset:Accum:
T4: 2
75000
Base: 0.01
Preset:Accum:
T4: 0
30000
Base: 0.01
DNT4:0
DNT4:0
DN
DNT4:1
DNT4:1
DN
DNT4:2
DNT4:2
DN
Preset:Accum:
C5: 0
500
CTU
I:0/3 T4:0
RES
I:0/3 T4:1
RES
I:0/3 T4:2
RES
O:0/3 C5:0
RES
C5: 0
DN
EN
EN
EN
ENCar arrives limit switch ON
Limit switch ON Washer ON
Washer ON: (i) Soapy water SPRAY ON (30 secs) (ii) Rinse: clean water SPRAY ON (30 secs) (iii) Automatic scrubber brushes car (15 secs) (iv) After washing 50 cars, the scrubber brush Auto-change
Programming a PLC
(1) Hand held console (direct feed of program into PLC)
(2) Computer-interface:(i) Complete the program on a computer(ii) Test the program on PC(iii) Upload the program to the PLC processor memory (persistent)(iv) Connect external Inputs and Outputs(v) Run the program on PLC