In industrial automation, the words permissive and interlock are often used as if they mean the same thing.
They do not.
Both are conditions that influence whether equipment is allowed to operate, …
Read MoreIn industrial automation, the word alarm is often used for almost everything that goes wrong.
A motor fails to start.
A tank reaches a high level.
A VFD trips.
A communication module disconnects.
An operator …
Read MoreA PLC program can work perfectly and still be difficult to troubleshoot.
That distinction matters.
When we first learn ladder logic, the goal is usually simple:
Make the motor run.
Later, the goal becomes …
Read MoreOne of the most useful PLC programming patterns a technician can learn is also one of the simplest:
Trigger → Hold-In → Interrupt
The idea is straightforward.
Something starts the action.
Something keeps it …
Read MoreIn industrial PLC programming, there are often several ways to make the same machine work.
Two of the most common methods for maintaining a control condition are Seal-In logic and Latch/Unlatch …
Read MoreWhen working with Allen-Bradley ControlLogix or CompactLogix systems, one of the first architectural decisions a programmer eventually faces is how to handle physical I/O inside the PLC program.
At the beginning, …
Read MoreIn the first article of this series, we introduced the idea of separating physical PLC I/O from application logic.
Now we can address one of the most common questions in Allen-Bradley …
Read MoreIn the previous article, we compared three common ways of representing PLC I/O:
Direct physical I/O
Alias Tags
Mapped controller tags
Now it is time to build the mapping layer itself.
For digital signals, one …
Read MoreIn the previous article, we built an I/O mapping layer using individual instructions.
For digital signals, we used logic such as:
XIC Physic
al_Input
OTE Internal_Tag
For numeric values, we introduced:
MOV Source Destination
This approach is …
Read MoreIn the previous articles, we built an I/O architecture using:
Direct physical I/O
Alias Tags
Individual mapped tags
XIC/XIO and OTE
MOV
COP
CPS
These methods allow us to separate physical hardware from application logic.
But as the machine …
Read More