At Beacon Industries, today marks an important milestone in our PLC development journey.
For many years, most of our lift and elevator control systems were programmed using Ladder Logic. This approach has been widely used in industrial automation because it closely resembles traditional relay circuits and is familiar to electricians and maintenance technicians.
However, as our products become more intelligent and control requirements continue to grow, we have started taking an important step toward Structured Text (ST) programming — a high-level language defined in the IEC 61131-3 standard.
Recently, we completed our first simple two-floor lift program entirely written in Structured Text.
Why We Decided to Move Beyond Ladder Logic
Our previous ladder programs were usually developed by our electricians according to the functions required by each lift project.
While Ladder Logic works well for many applications, it also has several limitations:
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Complex logic often requires many rungs and graphical elements.
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Programs become increasingly difficult to read as functions expand.
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Troubleshooting large programs can become time-consuming.
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Code reuse and modification are less convenient.
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Advanced functions often make ladder diagrams visually crowded.
As our control systems continue to evolve, we found that Structured Text provides a much clearer and more scalable approach.
Our First Structured Text Program
The following program is our first practical Structured Text application for a simple two-floor lift:
IF X012 THEN
IF NOT M0 AND NOT X014 AND (X003 OR M3) AND NOT M4 AND NOT X001 THEN
M3 := TRUE;
ELSE
M3 := FALSE;
END_IF;
IF (X004 OR M4) AND NOT M3 AND NOT X002 AND X013 THEN
M4 := TRUE;
ELSE
M4 := FALSE;
END_IF;
ELSE
M3 := FALSE;
M4 := FALSE;
END_IF;
IF M3 AND NOT Y000 AND NOT X014 THEN
Y001 := TRUE;
ELSE
Y001 := FALSE;
END_IF;
IF M4 AND NOT Y001 THEN
Y000 := TRUE;
ELSE
Y000 := FALSE;
END_IF;
Although the program is relatively simple, it successfully demonstrates the core movement logic of a two-floor lift.
Functions Implemented
This first Structured Text program already includes several essential elevator functions:
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Two-floor lift operation.
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Up and down travel control.
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Safety circuit monitoring.
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Safety edge protection.
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Upper limit safety protection.
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Basic interlocking logic.
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Motor direction control.
These functions make the program suitable for a standard two-floor freight lift or goods lift application. View our full range of industrial lift products to see how these control systems are applied in practice.
Advantages of Structured Text
After completing this first project, several advantages became immediately clear.
Better Readability
The logic flow is much easier to understand compared with multiple ladder rungs.
Easier Expansion
Additional functions such as automatic doors, floor selection, fault diagnosis, or maintenance modes can be added more conveniently.
Reduced Complexity
Complex conditions can be written in a single statement instead of multiple graphical elements.
More Software-Oriented Development
Structured Text allows us to approach lift control from a software engineering perspective rather than only an electrical wiring perspective.
This Is Only the Beginning
This first program is intentionally simple. It serves as a learning platform and a starting point for future development.
Our next goals include:
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Multi-floor lift control.
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Fault diagnostics.
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HMI communication.
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Parameter settings.
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Maintenance modes.
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Automatic leveling functions.
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Door control logic.
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Safety monitoring systems.
The transition from Ladder Logic to Structured Text represents an important step in our PLC development capabilities.
For many years, our lifts have been built through practical electrical experience. Today, we are beginning to combine that experience with modern programming methods.
This small two-floor program may be simple, but it marks the beginning of a new direction for our control systems and future elevator development.
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