# PLC Program to Operate Light as an Emergency Signal

This is a PLC Program to Operate Light as an Emergency Signal.

Problem Description

Boiler is being operated and monitored using a PLC. Temperature set point of boiler is 600°C and maximum temperature limit is 610°C. If temperature rises above its maximum limit. Hooter and emergency lights are activated in order to inform operator. Implement this in PLC using Ladder Diagram programming language.

Problem Solution
• There are two methods to solve this problem. One is by using stack operation and the other one is by using sequencer output method.
• Sequencer output method is best suited for this problem since very less configuration is needed and program length is also reduced.
• In this method, we need to assign SQO instruction by configuring all the parameters given in the instruction.
• Alarm signal must be continuous until operator turns it off manually.
• Sequencing of Lights and Hooter is done here by using SQO Sequential Output to operate lights and hooter.
• Set timer to activate and deactivate hooter and lights or to be précised, change sequence of output.
• Let’s say, these both outputs are energized for 1sec and de-energized for next 1sec.
• In sequencer output, the start position is all zeros. So to start the actual function of output sequence, Position 1 is determined as starting sequence while programming.
PLC Program

Here is PLC program to Operate Light as an Emergency Signal, along with program explanation and run time test cases.

```List of Inputs and Outputs
I:1/0	= Start 				(Input)
I:1/1	= Stop					(Input)
O:2/0	= Master Coil				(Output)
T4:0	= Timer to update output sequence	(Timer)
SQO	= Sequencer output			(Sequencer)
O:2/0	= Emergency Red Light (From O:2)	(Output)
O:2/1	= Hooter	      (From O:2)	(Output)
R6:0	= Control Register			(Register)
N7:0	= File register				(Register)
-(RES)- = Reset outputs and Position of SQO	(Logical)```

Ladder Diagram to control light as emergency signal with hooter

Program Description
• File; #N7:0 and File length is 2, hence output sequence is varied from N7:0 and N7:1 with each input.
• Destination is set to O:2 hence with each transition, N7:0 and N7:1 are moved to O:2 with masking.
• O:2/0 and O:2/1 are used as the output address to Emergency Light and a Hooter, hence Mask has value 0003h which means data flow of N7:0/0, N7:0/1, N7:1/0 and N7:1/1 are passed to O:2/0 and O:2/1, and remaining bits are blocked.
• Control parameters are assigned to register R6:0.
• Sequence of Light and Hooter to be operated are stored in the registers N7:0 and N7:1 as following.

• Time base is set to 1sec, hence after every 1sec, output sequence is changed to its next register pattern output which is then transferred to O:2 and O:2/0-O:2/1 are energized accordingly.
• As we can see, N7:1 and N7:2 have the exact opposite bit pattern. So, these bits are set to 1 for 1 cycle and reset for the next cycle. These bits are used to operate Hooter and a Light.
• So when I:1/0 is pressed, during position 0, outputs and remain in OFF condition and are energized when SQO is at position 1.
• When Stop PB with address I:1/1 is pressed, Position is reset to 0 and all the outputs are de-energized.
Runtime Test Cases

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