Assignments on PLC Ladder Programming

A) Simple PLC ON-OFF Instructions:

  1. Develop OR, AND, NOT, NOR, NAND, and EX-OR logic using two toggle switches and output is given to a pilot lamp.
  2. A fan is started and stopped from three different locations. Each location has a start and stop pushbutton.
  3. Develop a ladder program for a motor with START and STOP pushbuttons. Green lamp should be ON, when motor is running and motor should stop suddenly when bearing temperature is high, with red lamp indication.
  4. In a certain bank, each of three bank officers has a unique key to the vault. The bank rules require that two out of the three officers be present when the vault is opened. Develop the ladder program that will unlatch the door and turn on the light when two of the three keys are inserted.
  5. Draw the ladder program for following application. There are four hazardous inputs to the alarm system that goes ON when a fault occurs. The sequence is,
    1. If any one fault occurs, nothing will happen.
    2. If any two faults occur, Red lamp will be ON.
    3. If any three faults occur, Buzzer will be ON.
    4. If all four faults occur, send alarm to fire department.
  6. On the automatic lathe machine, the carriage ( tool-post ) should move in between headstock and tailstock continuously. ( i.e. reciprocating motion of carriage). Use limit switches to detect the positions.
  7. The elevator system employs a platform to move object up and down. The   objective is that, when ‘up’ pushbutton is pressed, the platform carries a material to ‘up’ position and when ‘down’ pushbutton is pressed, the platform moves to down position. Use limit switches for highest and lowest position and two relays to change the direction of motor.
  8. Develop ladder program for bottle filling station having sequence as follows:

                  a)Start the conveyor.
                  b)When bottle is in position, stop the conveyor and open solenoid valve.
                  c)When bottle is full that is detected by optical proximity switch, close the solenoid valve.
                  d) Go to step 1 for next bottle.

     9.  Simple on – off program.      

Requirements: there are two buttons & three lamps. (Red, Blue, Green)

    • When PB 1 is pressed then only Blue & Green lamp on. 
    • When PB 1& PB 2 pressed simultaneously, then only Red lamp on.
    • When PB 2 pressed then only Green lamp on.

10.   Pump on / off programme.
          There are four push buttons
           PB 1: Pump one start.
           PB 2: Pump one stop.
           PB 3: Pump two start.
           PB 4: Pump two stop.

  •  Two feedbacks (for pump one & pump 2) from contactor, which in turn makes pump on.
  • Two lamps (Green lamp for both pumps on, red lamp for one or both pump off / trip) and two relays (ready for pump 1, relay for pump 2)
  • When PB 1(pump 1 start push button) is pressed then Pump one start. When PB 2 (pump 1 stop push button) pressed then pump1 stop.
  • Similarly When PB 3 (pump 2 start push button) is pressed then Pump 2 starts. When PB 4 (pump 2 stop push button) pressed then pump 2 stop.
  • When both pumps are on the green lamp is on. If pump 1 or pump 2 ON but after 1 sec. Feedback not ON then red lamp starts flashing. 

11.Staircase lamp ON / OFF

  •  There are two push buttons PB1 & PB2. PB1 is fixed at ground floor and PB2 is     fixed at upper floor of staircase. A lamp is fixed at middle position.
  • When PB1 is pressed, lamp should get ‘ON’, if lamp was in the OFF state   otherwise the lamp should go OFF, if the lamp was in the ON state.
  • The same thing must happen when the PB 2 is actuated.
  • In brief, ON & OFF the states of the lamp must be achieved alternatively using any push button whenever they are actuated.

12.      Tank controller 

  • There are two pushbuttons (PB1 pump start, PB 2 pump stop), level sensors (LS1 top tank high level, bottom tank high level, LS 2 bottom tank low level). Two lamps (L1 pump on indicator, L2 water level error) & 1 relay for pump on.
  • When pump start PB is pressed then gets ON & pump on indication glows. If pump stop PB is pressed then pump is off.
  • There are two conditions for starting of pump.
  • Level in bottom tank is above low level
  • Level in top tank is below high level.
13.There is one push button (PB 1) & one lamp (L1). First time when push button          (PB1) is pressed then lamp becomes on. Next time when the same push button is pressed then lamp goes off.

14. Star –delta connection.
There are only 2 push buttons. Start push button & Stop push button. System operates only in Auto Mode.
When start push button pressed main contactor will get energized timer also get started. Initially star connections will come into picture as motor fetches extracts current. Then rate current limit for its smooth functioning.  This is only for the first few seconds. Once motors starts. On the done bit of timer circuit switches the delta connection.

15. Direct ON line start   
There are push buttons, start PB, Stop PB System operates in only in one mode.
1. Auto mode
A) In initial condition for Direct on line, stop button is not pressed.
B) Start button is also not pressed.
C) When start push button is pressed. Corresponding output gets ON.
D) In this step we used to latch the output so that respective action of start push button can b e avoid.

16. Pump Automation.
There are two push button start PB, Stop PB. There are one switch Auto / manual switch.
System operates in 2 modes
1) Auto mode
2) Manual mode
 Auto mode:

  • Initially selector switch is ON. Auto mode is selected; both push buttons are not pressed. Cycle is not going to start.
  • as start push button is pressed & system is on auto mode cycle starts, if tanks to be filled are less than 5 only pump  1will be ON. If tanks increase up to 5 or grater than 5 than pump 2 will starts. Fault lamp blinks when any problem is their during a run of pump 1 or both (pump 1 & pump 2) in response to action to fault lamp is given by starting of pump 3 which is stand by pump.
Manual mode:
  • Initially all three pumps are off. Usually this mode is used to isolate a problem in any of part of the system.
  • In this mode we can start or stop all the pumps (including stand by pump) or in any of the combination. There are no any restriction of system interlock while making pump ON or OFF in manual mode.
  • I.e. user can run a system according to the time & requirement.

B) Assignments on Timer instructions :

  1. A small heating furnace has two heating elements that are energized in two stages, 3 minutes apart. That is when the furnace is turned ON, the first heating element comes on right away, and the second element comes on 3 minutes later. A temperature switch will shut down the furnace if it is too hot. Draw the ladder diagram for control circuit.  
  2. Develop a ladder program for sequencing for three motors of 0.5 HP, 1 HP and 3 HP. The expected sequence is 3-1-2. While starting these motors, provide delay of 60 seconds. For the safety of the systems, every motor has to satisfy the following interlocks,
      1. Bearing temperature high for all three motors.
      2. Winding temperature high for all three motors.
      3. Over current protection high for all three motors.
  3. A batch process, which involves filling a vat with a liquid, mixing the liquid, and draining the vat is automated with a PLC. The specific sequence is as follows, when start pushbutton is pressed,                             
    1. An inlet valve opens and lets a liquid into vat until it is full.
    2. The liquid in the vat is mixed for 3 minutes.
    3. A drain valve opens and drains the tank.
  4. We are provided with two pushbuttons and one lamp. Develop ladder program to flash a lamp, when start pushbutton is pressed (flashing rate: 2 sec.) .the lamp should be OFF upon pressing stop pushbutton. 
  5. Explain the working of CSTR and develop ladder diagram for CSTR. Draw the process diagram. Indicate clearly inputs and outputs. Write down the sequence of events. Mention the assumptions made if any.
  6. You are required to develop a ladder diagram for pick and place type bottles on conveyor belt system.
      1. Draw process flow diagram
      2. List inputs and outputs
      3. List the instructions.

C) Assignments on Timer-Counter Instructions:

  1.  Develop a physical ladder for an automatic washing machine with front-loading system. Assume suitable washing sequence.
  2. There is one selector switch. (Cycle starts) one push button, one pump & two lamps (red & green)
    1. When selector switch is ON then pump gets on & after 6 seconds, pump becomes OFF, after two seconds pump again becomes on, which continues.
    2. If pump gets on, and Off 5 times then cycle stops & cycle complete indication is on.
    3. When cycle starts then cycle start indication is ON.
    4. To restart operation cycle first press reset push button & then makes selector switch on. 

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