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Phoenix Control Systems Ltd
 
Automation Ready Panels
Control Systems International
 
Shawa Technocrafts Pvt Ltd
Text Link ads rent Buy now
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    PLC programming technology and HMI interface design English database

    PLC, DCS, HMI and SCADA product application technical articles
    xiangjinjiao
    Create a PLC program for alarm indication in the process control industry. Learn the PLC programming with this industrial example.
    Alarm Indication in Process Control
    In many industries there are lots of machines which are performing many tasks automatically. There are many sensors and components used in system or process.
    Sometimes operator may not be identify the problems of machine or system by visual observations. And also sometimes there will be a chance that machine stops working due to some problem in it.
    Problem Diagram

    PLC Solution
    We can solve this problem by adding alarms in system or process. Alarms are added to alert operator to monitor that machine/process about to cross its limit values or already crossed the limit.
    Alarms are indicated to the operator by annunciator or horns, and lights of different colors on the panel. (For example, green lights meant OK, Yellow meant not OK, and Red meant BAD.)
    The purpose of alarms is to use automation to help human operators as they monitor and control processes, and alert them regarding abnormal situations of the plant.
    Incoming/Input process signals are continuously monitored, and if the value of a given signal moves into an abnormal condition, a visual and/or audio alarm informs the operator regarding the situation.
    We can configure alarms for system by different ways, such as MIMIC, indication lamps on panel board, SCADA, HMI etc.
    For our problem discussions, we considered one simple system and configure alarms for the system.
    For example consider one filling and discharging process and in this system we want to consider some alarms, we will show alarm by using lamps on panel board.
    For example, consider following alarms for our system,
    Emergency stop pressed Feed valve open error Feed valve close error Discharge valve open error Discharge valve close error Here all are errors, so we take all red color indication as shown in above figure.
    List of Inputs & Outputs in PLC
    Inputs List
    Cycle START : I0.0 Cycle STOP : I0.1 Low Level Switch, LL : I0.2 High Level Switch, LH : I0.3 Feed VLV open LS : I0.4 Feed VLV close LS : I0.5 Disc. VLV open LS : I0.6 Disc. VLV close LS : I0.7 Emergency STOP : I1.0 RESET : I1.1 Output List
    Cycle ON : Q0.0 Feed valve : Q0.1 Disc valve : Q0.2 BUZZER : Q0.3 Emergency STOP pressed : Q0.4 (Indication lamp) Feed VLV open error : Q0.5 (Indication lamp) Feed VLV close error : Q0.6 (Indication lamp) Disc VLV open error : Q0.7 (Indication lamp) Disc VLV close error : Q1.0 (Indication lamp) PLC Program for Alarm indication in Process Control









    Logic Explained
    In this application, we have used Siemens S7-300 PLC and TIA Portal Software for programming.
    Network 1:
    In network 1, we used latching circuit for cycle ON (Q0.0) output. It can be started by pressing cycle START PB (I0.0) and STOP by pressing STOP PB (I0.1).
    When cycle will be START then system checks level of the tank. If tank level is low then the feeding process will start and if tank level reaches high then Discharge cycle will START.
    Network 2:
    When tank reaches low level then LL (I0.2) will be activated and feeding cycle will be ON. Here we have taken NC contact of LH (I0.3) so when PLC will detect high level then it will STOP feeding cycle.
    Network 3:
    When tank reaches high level then LH (I0.3) will be activated and discharging cycle will be ON.
    Here we have taken NC contact of LL (I0.2) so when PLC will detect low level then it will STOP discharge cycle.
    Network 4:
    When system receives Emergency STOP (I1.0) input then it will activate the Emergency STOP pressed output (Q0.4) and alarm indication will be provided to the operator.
    Network 5:
    In this network we have configured feed VLV open error alarm (Q0.5), when feed valve is ON and Feed VLV open LS (I0.4) is not detected then timer will START and after 5s Feed VLV open error alarm is ON (Q0.5).
    Network 6:
    In this network we have configured feed VLV CLOSE error alarm (Q0.6), when feed valve is CLOSE and Feed VLV CLOSE LS (I0.5) is not detected then timer will START and after 5s Feed VLV CLOSE error alarm is ON (Q0.6).
    Network 7:
    In this network we have configured Disc VLV OPEN error alarm (Q0.7), when disc valve is ON and disc VLV OPEN LS (I0.6) is not detected then timer will START and after 5s disc VLV OPEN error alarm is ON (Q0.7).
    Network 8:
    In this network we have configured Disc VLV CLOSE error alarm (Q1.0), when disc valve is CLOSE and disc VLV CLOSE LS (I0.7) is not detected then timer will start and after 5s disc VLV close error alarm is ON (Q1.0).
    Network 9:
    In this network we have configured BUZZER for all alarms, when alarm detected then BUZZER (Q0.3) will be activated and it can be RESET by pressing RESET (I1.1).
    Network 10:
    Operator can reset the BUZZER by pressing RESET (I1.0)
    Test Cases

    Note: The above PLC Logic provided for basic idea about application of PLC in Alarm Indication of a Process. The Logic is limited and not complete application.
    xiangjinjiao
    This is the PLC program for the automatic bottle rejection system. Learn the ladder logic with this PLC exercise and solution.
    Automatic Bottle Rejection
    Problem Description
    Nowadays Automation in industries is necessary for Accurate and fast Production.
    Let’s Take an Example of soda bottle companies, where the belt conveyor is used for transferring the bottles from one station to another station.
    But before bottles reach at soda filling station it is necessary to make all bottles are in standing position for further processing
    A fallen bottle on the conveyor may create a problem in the next process. so here we discuss a simple PLC Logic that handles the fallen bottle.
    PLC Problem Diagram

    PLC Problem Solution
    So for that we use PLC system at filling station, which reject the fallen bottle from the conveyor & clear the path for the next process.
    This process is made by using sensors & actuators. We use pneumatic piston cylinder assembly for pushing the fallen bottles from the conveyor.
    When conveyor is running, then all bottles transfer form one station to other station for next process. There are two sensors are used, for standing and fallen bottles detection, one pneumatic cylinder for pushing the fallen bottle from the conveyor.
    List of Inputs/Outputs
    Inputs List
    Start PB : I0.1 Stop PB : I0.0 Sensor X1 : I0.2 Sensor X2 : I0.3 Outputs List
    Cycle ON : Q0.0 Conveyor : Q0.1 Cylinder : Q0.2 PLC Program for Automatic Bottle Rejection System

    PLC Program Explanation
    In this application, we have used Siemens S7-1200 PLC and TIA Portal Software for programming. We can also design this logic with relay circuit also.
    Network 1:
    In Network 1, we have taken cycle ON condition for machine. Here we have taken START PB (I0.1) for starting the cycle and STOP PB (I0.1) for cycle STOP.
    We have taken parallel output of conveyor (Q.1) with cycle ON (Q0.0) so we can operate conveyor with cycle ON condition.
    Network 2:
    In Network 2, we have taken sensors X1(I0.2) and X2(I0.3) as inputs. We used NO contact for X2 (I0.3) sensor and NC contact for X1 (I0.2) sensor.
    When Bottles are transferring on the conveyor, these sensors sense the position of the bottles whether they are standing or fallen.
    Sensor X2(I0.3) sense down position of the Bottle & Sensor X1(I0.2) Sense top position of the bottle.
    In PLC, we designed the circuit which follows command that if sensor X2(I0.3) sense the bottle & sensor X1(I0.2) does not sense the bottle then the pneumatic actuator (Q0.2) will come in action & it will reject the bottle from the conveyor.
    After this, the perfect bottles will go in the soda filling station & whole cycle will be completed.
    Result

    Note: The above PLC Logic provided for basic idea about application of PLC in Automatic Bottle Rejection Handling System. The Logic is limited and not complete application.
    xiangjinjiao
    PLC Program for Daily Production Record. Learn the problem description with a detailed explanation of the ladder logic.
    Daily Production Record
    Problem Description
    In many industries, It is required to count the number of products that are made in one day and it is very necessary for selling the products or tracking the production quantity on a daily basis.
    In the olden days, human operators were allotted for counting the final products but because of some human errors, precise counting is not possible. Therefore we cannot get proper counting of all products and are unable to track the production quantity effectively.
    Mostly these types of problems occur in food and beverage industries, box packaging industries, bottle filling applications etc. So we can use a simple PLC based logic to track the daily production and to record it electronically.
    Problem Diagram

    PLC Solution
    Here we will solve the problem of counting of final products by using sensors and PLC programming. First sensor sense the product and counts the quantity and the value will be shown on the digital display (as shown in above figure).
    For easy explanation, we will consider one simple example of empty box counting system. In this system empty boxes are travelling form first process to second process (say one place to another).
    Sensor is used for counting the empty boxes. So when sensor will detect empty box then display will start , say starts count from  1 and this is done by simple logic.
    Every 24 hours / after one day, we can reset the counter value by using RESET button. Here we will consider two batches of production for easy explanation.
    And also we have considered two batches completion indications for operator for each batch which will display on the Local Panel. By PLC logic we will implement the desired logic.
    So when any batch will be completed then indication lamp will be ON as per PLC program.
    Once production target will be completed, display counter can be reset by using RESET button.
    List of Inputs/Outputs
    Inputs List
    Box detector Sensor: I0.0 Reset: I0.1 Main SWITCH: I0.2 Outputs List
    Target completed: Q0.0 Batch 1 completed: Q0.1 Batch 2 completed: Q0.2 Ladder Diagram for Daily Production Record

    PLC Program Description
    In this application, we have used Siemens S7-1200 PLC and TIA Portal Software for programming.
    Network 1:
    In Network 1 we used Main SWITCH (I0.2) to start the system/batch and we used NO contact of box detector sensor (I0.0) in series. Here we considered one UP counter so when box detector sensor (I0.0) detects  the box then counter will starts counting.
    Here also we have taken target completed output (Q0.0) for target completion indication for the operator indication on the panel. By pressing RESET button (I0.1) operator can RESET the old production record.
    Counter operation is used to count the products, in which RESET (I0.1) used for reset the production record. And Preset value (PV) is 20 products. Counter value (CV) is MW2 indicates the actual number of products detected by sensor & this value will be used in the following rungs to track the batch status.
    Network 2:
    In Network 2 we used batch1 logic from counter block output CV. Here we used comparator for counting 10 boxes for batch 1 and when it will be completed then batch 1 completed lamp (Q0.1) will ON. In this add equal to equal comparator in which input is (MW2) and for 10 products.
    Network 3:
    In network 3 we used batch 1 logic from counter block output CV. Here we used comparator for counting 20 boxes for batch 2 and when it will be completed then batch 2 competed lamp (Q0.2) will ON
    And this way we can decide that how many products and batches are produced.
    Runtime Test Cases

    Note: The above PLC Logic provided for basic idea about application of PLC in industrial production record. The Logic is limited and not complete application.
    xiangjinjiao
    This is the PLC Program for Sequential Motor Operating System.
    Sequential Motor Control
    Problem Description
    In many industries, there are lots of motors are used. Sometimes we need to start more than one motor in an application.
    When we have a low incoming power supply rating, then there is a chance the incoming MCB will trip when one or more motors will START in parallel because they will consume more power.
    Here we will consider one similar example where we START each motor one by one.
    Problem Diagram

    Problem Solution
    The problem can be solved by using PLC programming or relay logic.
    In this case, we have to operate motors sequentially. There are total 3 motors to be controlled in a sequence. so that each motor will start sequentially, say Motor 1 will START then after some delay then motor 2 will start and after some delay motor 3 will start.
    So that whole operation will take 10 seconds to start all motors in a sequence. By providing this delay we can avoid the problem of taking large current by motors during initial stat up.
    All motors will be operate in the sequence and 5 seconds time delay is to be provided between operations of each motor.
    Here will write logic for sequential operation for motors using PLC.
    List of Inputs & Output
    Inputs List
    Start PB : I0.0 Stop PB: I0.1 Outputs List
    Cycle on : Q0.0 Motor 1: Q0.1 Motor 2 : Q0.2 Motor 3 : Q0.3 PLC Ladder Diagram for Sequential Motor Control

    Ladder Logic Explained
    In this application, we used Siemens S7-1200 PLC and TIA Portal Software for programming. We can also design this logic with relay circuit.
    Network 1:
    In Network 1, we wrote logic for cycle ON condition. Here cycle ON (Q0.0) lamp will indicate cycle status. Cycle can be started by pressing START PB (I0.0) push button and can be Stopped by pressing STOP PB (I0.1) push button.
    When cycle will be ON, at same time Motor 1(Q0.1) will be Started. And at the same time, timer instruction will be executed.
    Network 2:
    In Network 2, the NO contact of Motor 1  starts Timer T1  and when Timer for Motor 2 (Q0.1) will reach the set value 5 seconds. Then NO contact of the T1 will START the Motor 2 (Q0.1).
    Network 3:
    In Network 3. we have taken logic for motor 3. Here we have given NO contact of motor 2 for starting the timer of motor 3. When T2 will reach the set value 5s , the NO contact of the T2 will START the Motor 3(Q0.0).
    When STOP PB (I0.1) will be pressed then NC contact will be activated which makes Cycle (Q0.0) OFF. And also motor 2 and 3 will stop working.
    Runtime Test Cases

    Note: The above PLC Logic provided for basic idea about application of PLC in Sequential Motor Control. The Logic is limited and not complete application.
    xiangjinjiao
    This is PLC Program for Two ways switch logic for staircase light in house
    PLC Two Way Switch Logic
    In duplex type house there are ground floor and first floor and sometimes second floor also.
    Sometimes people need to go from ground floor to first floor or from first floor to ground floor by staircase provided in house.
    But in staircase there is no sunlight so people need a lamp/light to see the steps of the staircase easily.
    Here we are using a simple PLC to control this lamp using two switches, one switch at ground floor and second switch at first floor to control one lamp as shown in below figure.
    Note : we can also build the circuit using simple relays/switches also. This article only for understanding the basic concept of 2 way switch using  a PLC Ladder Logic.
    Image

    Solution
    We will solve this problem by simple automation. As shown in figure consider one simple house with one floor and staircase is provided in the house.
    Here we will set lighting system for the users to switch ON/OFF the light whether they are on bottom of the stair or at top.
    We will provide separate switch for each floor as shown in above figure.
    PLC I/O Requirements
    Digital Inputs
    SW1 : I0.1 SW2 : I0.2 Digital Outputs
    Lamp : Q0.0 PLC Progam for Two-way Switch

    Program Explained
    For this application, we used S7-1200 PLC and TIA portal software for programming. In above program, we have added two NO contacts of SW 1 (I0.1) and SW 2 (I0.2) in series and NC contacts of SW1 (I0.1) and SW2 (I0.2) in parallel of this series SW1 & SW2 NO Contacts. If the status of the bottom switch (SW1) and status of the top switch (SW2) are same then lamp will be ON. And if either status of the bottom or top switch is different from other then lamp (Q0.0) will be OFF. When lamp (Q0.0) is OFF then user can ON the lamp by changing status of any switch. Also user can turn OFF the lamp by changing the status of one of the two switches. Result

    Note: The above PLC Logic provided for basic idea about application of PLC for Two Way Switch Logic. The Logic is limited and not complete application.
    xiangjinjiao
    This is a PLC Program for Forward and Reverse control for 3 Phase Asynchronous Motor.
    3 Phase Motor Control using PLC
    Problem Description
    There are lots of motors and conveyors used in industries for different purposes.
    In some cases, motors or conveyors need forward and reverse operation for some control purpose.
    For example overhead crane, in crane every time operators moves it forward and reverse for material handling.
    So we can use PLC systems for programming the motor for forward/reverse operation.
    Problem Diagram

    Problem Solution
    In this case, we need to operate motor in both direction, that can be possible only by forward/Reverse Control Relay Circuit or through Logic.
    Here we solve this problem by using simple Forward/Reverse Control Logic in the PLC.
    So here we will consider one 3 phase motor for Forward and Reverse Operation.
    And we will take two contactors or relays for motor control because we need two different directions here i.e. Forward/Reverse. First contactor for Forward Direction control and Second contactor for Reverse Direction control of Motor.
    Also we should consider three push buttons i.e. for forward, reverse and stop functions of motor.
    So here operator will use FWD PB for forward operation, REV PB for reverse operation and STOP PB for stop function.
    PLC Inputs List
    FWD PB : I0.0 REV : I0.1 STOP PB : I0.2 Motor Trip : I0.3 PLC Outputs List
    Motor forward : Q0.0 Motor reverse : Q0.1 PLC Ladder diagram for Forward/Reverse control of Motor

    Ladder Logic Description
    In this application, we will use Siemens S7-1200 PLC and TIA Portal Software for programming. We can also design this logic with relay circuit. This circuit is also known as Forward/Reverse control for 3 Phase Induction Motor. We will write logic for forward condition in Network 1. Here we use the NO contact of FWD PB (I0.0) for forward operation of the motor, we are using push button so we need to use one NO contact of motor forward output coil (Q0.0) for latching purpose. (Push button only provides momentary contact and we need to latch the action so motor forward coil contact will be used) Put NC contact of motor reverse output (Q0.1) in series for unlatching the circuit because both forward and reverse should not run at the same time. Now write the logic for reverse condition in network 2. Here we will take NO contact of REV PB (I0.2) for motor reverse function and also take one more NO contact of the motor reverse output coil(Q0.1) for latching the motor reverse output (QO.1). (Push button only provides momentary contact and we need to latch the action so motor forward coil contact will be used) Here also put NC contact of motor forward output coil (Q0.0) in series for unlatching the circuit because both forward and reverse should not run at the same time. For interlocking purpose put NC contact of FWD PB (I0.0) in series with REV PB (I0.2) and put NC contact of REV PB (I0.2) in series with FWD PB (I0.0). Put NC Contact in series in both network so operator can stop forward or reverse rotation by pressing STOP PB Here we have used OLR for Protection of motor so add NC contact of Motor trip (I0.3) in series in both the network for motor protection Runtime Test Cases

    Note: The above PLC Logic provided for basic idea about application of PLC Logic for 3 Phase Asynchronous Motor Control. The Logic is limited and not complete application.
    leizuofa
    Assume there are sixteen stations along a conveyor system.
    The stations are numbered from 0-15 with station zero being the first (i.e. the point where parts enter the conveyor).
    Parts are to advance along the conveyor at the rate of one station every four seconds.
    A part may or may not be at a given station at any point in time.
    An input sensor I:0.0/0 is used to detect a part entering the conveyor.
    At station 5, parts are checked for defects and an input sensor I:0.0/1 is energized if the part is defective.
    At station 10, any defective parts are to be removed from the conveyor by energizing output O:0.0/0.
    Write an efficient ladder logic program for this process.
    PLC Conveyor Ladder Logic Program

    leizuofa
    Write the following PLC Program to Energize or De-energize the Outputs based on Events.
    A certain switch (I:1/0) is to start a process.
    The process is to run for 30 seconds, stop for 10 seconds and then repeat as long switch I:1/0 remains closed.
    Opening I:1/0 at any time is to reset all timers and de-energize all outputs. Output O:2/0 is to be energized during the 30s run period and output O:2/1 is to be energized during the 10s stop period.
    During the run period, a single output O:2/2 is controlled by input I:1/1. If I:1/1 is open (at the beginning of the run period) O:2/2 is to be off for the first 5 seconds then on for 10 seconds.
    If I:1/1 is closed (at the beginning of the run period) O:2/2 is to be off for the first 10 seconds then on for 15 seconds.
    Changing I:1/1 after the run period has begun should not change the above sequence. Output O:2/2 is always to be off during the stop period.
    PLC Energize or De-energize Outputs

    leizuofa
    Write a PLC Counters Program for the below example.
    PLC Counters
    A certain process is to count the number of true-to-false transitions on input I:0.0/0 for a 10 second period.
    Counting is to occur if input word I:0.1 has a value less than 10000 or greater than 20000.
    The 10 second counting period is to begin 15 seconds after the process starts. I:0.0/1 is a process start input and input I:0.0/2 is a process stop input.
    The count display is to be output to word O:0.0 only at the end of the count period.
    All outputs are to be de-energized 5 seconds after the count period.
    The process should repeat only after another distinct press of the process start input.
    Write an efficient ladder logic program for this process.
    PLC Logic

    leizuofa
    Write a PLC Logic GATE Program for the below plc example.
    Logic GATE Program
    Write a program that ANDs B3:0 with B3:1 when I:0.0/0 is energized, ORs B3:0 with B3:1 when I:0.0/1 is energized, XORs B3:0 with B3:1 when I:0.0/2 is energized and COMPLEMENTS B3:0 when I:0.0/3 is energized. B3:1 is to hold the result in each case.
    If more than one input I:0.0/0-I:0.0/3 is energized, only one of the operations will be performed.
    The precedence order for operations should be from AND (highest precedence) to COMPLEMENT (lowest precedence).
    PLC Ladder Logic

    leizuofa
    Write a PLC Timers Program for the following plc example.
    PLC Timers
    Construct a PLC timing circuit that will output (using output O:2/0) a 0.5 second pulse every two seconds (i.e. on for 0.5s then off for 2s).
    If a switch (using I:1/0) is closed and a 1 second pulse every two seconds if the switch is open.
    Ladder Logic

    leizuofa
    PLC tutorial explaining step by step procedure to program PLC for motor starter.
    Motor starters are of many types however the scope of this PLC tutorial is confined to simple motor starter.
    It should have the following provisions.
    Push button to start the motor : The motor should continue to rotate even when the push button is released. Stop Push button to halt the motor after it started. Over current protection : In case of over load, the motor should stop automatically by the signal coming from contactors of overload relay. Limit switch : It should prevent the motor from starting and can also stop the running motor. The motor starter should also have indicator (Lights) to show ON or OFF status of motor. Motor Electrical Schematic :

    The above figure shows the physical layout of motor starter however this would be designed through ladder logic in this PLC tutorial.
    Above figure does not show limit switch because it depends on external interlock like say level switch, flow switch, pressure switch etc… depending on application. if interlock not required then simply remove the symbol from the diagram and connect with simple wire.
    Ladder diagram for Motor starter :
    Following figure shows the ladder diagram for motor starter.

    Start Button I1 :
    Normally open contact (Make contact) is used because the motor should only start when the button is pressed.
    Stop Button I2 :
    Normally close (break contact) contact is used because the button should normally be closed or high so that the motor keeps on running. It should open when the button is pressed. It is opposite to start push button.
    Overload relay I3 :
    In normal condition, this relay should allow the motor to rotate so normally close contact is selected for it. In case of overload it will stop the motor by opening its contact.
    Limit switch I4 :
    The motor should only rotate when the limit switch is closed therefore normally open contact is used.
    Output Q1, Q2, Q3 :
    Relay coil Q1, Q2 and Q3 represent motor output, motor indication ON and indication OFF respectively.
    ON indicator gets input from normally open input which depends upon output Q1. OFF indicator is fed by normally close input which depends upon output Q2.
    Input Q1 ( for continuous rotation):
    Since it is required that once push button is pressed, motor should run continuously even if the push button is released.
    To achieve this part, an input Q1 (normally open) is used and connected in parallel with I1. This input depends upon output Q1.
    When output is high, input Q1 is also high. Since input Q1 provides parallel path with I1, so if any of them is to be high, motor will run (if other conditions are also satisfied).
    Start button (Normally open), stop button (Normally close), overload relay (Normally close) and limit switch (Normally open) are connected in series. So motor will run if start button is pushed, stop button is not pressed, overload relay is not picked and limit switch is closed.
    Note : This post for educational or reference purpose only. For a live  circuit, there will be some additions to the above circuit like safety related, as per application, some interlocks etc.
    leigehong
    PLC Programming Tutorials for PLC Conveyor Motor Ladder Logic or Conveyor Belt Control using a programmable logic controller (PLC).
    PLC Conveyor Motor Ladder Logic

    Objective: The sequential tasks as follows
    When START button pressed Motor will be started RUN (Green Lamp) indication lamp will be activated Motor Running, so Box will start Move Proximity Sensor will detect when the box arrives at other end Motor will be stopped RUN (Green Lamp) indication lamp will be de-activated STOP (Red Lamp) indication lamp will be activated An Emergency Stop push button will be used to stop the motor at any time. Relay Schematic

    R : STOP Indication lamp, G : RUN Indication lamp, M : Motor, OL : Overload Relay (Motor Protection Relay), LS1 : Proximity Switch, PB1 : Start push button, PB2 : Emergency Stop Pushbutton, CR : Contractor Relay Operational Sequence
    Start button is actuated. CR1-1 closes to seal in CR1 or to latch the start command CR1-2 opens, switching the red stop pilot light off CR1-3 closes, switching the green run pilot light on CR1-4 closes to energize the motor starter and motor The box/package moves, and proximity switch (LS1) detects the box when it reached and de-energize coil CR1 CR1-1 opens to open the seal-in contact ( unlatched start command) CR1-2 closes, switching the red pilot light on CR1-3 opens, switching the green pilot light off CR1-4 opens to de-energize the starter coil, stop the motor, and end the sequence PLC Ladder Logic

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