Problem Description

Ladder Diagram to reset all non-retentive outputs (Allen Bradley)
Program Description

As the theory of MCR describes, it needs to be turned on to be inactive.

When I:1/0 is high, all the rungs perform operation normally which are in between RUNG000 to RUNG004.
Others are independent of MCR.

When I:1/0 goes low, it forces all the NON-RETENTIVE outputs O:2/1 and O:2/2 to be de-energized.

However O:2/3 is not affected by MCR since it is –(L)– instruction.
Runtime Test Cases
MCR
inactive
MCR active
PLC Program to Operate Light as an Emergency Signal
This is a PLC Program to Operate Light as an Emergency Signal.

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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)

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