Problem Description

Runtime Test Cases
During
 
timer
 
on
 
condition
After 10secs
PLC Program to Latch and Unlatch an Output by Sealing
This is a PLC Program to Latch and Unlatch an Output by Sealing.
Problem Description
Implement Latching and Unlatching of Output without using manufacturer provided Latching and
Unlatching Instructions. That is called Latching by Sealing of contacts.
Problem Description

In many PLCs, Latching and Unlatching instructions are not available to latch and unlatch outputs directly.

To achieve this, Seal in contact must be used to obtain similar level of Latching.

This technique of latching is called Latching by Seal in contact.

This seal in contact must be used in parallel with the main input Start Push Button and address of this
parallel contact must be same as Output of which we want to latch.

By performing this simple technique, we can obtain Latching of output that of similar to Latch/Set/Keep and
Unlatch/Reset/Bit instructions of Allen Bradley/Siemens/Omron PLCs respectively.
PLC Program

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Here is PLC program to Latch and Unlatch an Output by Sealing, along with program explanation and run
time test cases.
List of Inputs and Outputs
I:1/0
=
Start Push Button (Input)
I:1/1
=
Stop Push Button (Input)
O:2/0
=
Output (Input & Output)
Ladder
 
Diagram
 
to
 
obtain
 
Latching
 
&
 
Unlatching
 
Fig.1
Ladder
 
Diagram