Factory Digitalization Ver14. _ How to Deal with Black Box PLCs

Shigenori Tanaka
1 時間前
読了時間: 3分

　　　　　　　　　　　　　　　　　　　　　　　　　Jun 14, 2026

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When manufacturers express the need to “visualize equipment live data,” the first idea that many companies consider is extracting data directly from the PLC.

However, for large Western-made equipment—especially those using closed PLCs such as Siemens or Allen‑Bradley—this approach is often difficult or unrealistic.

The reason is simple: the PLC itself is a black box.

1. Why Direct PLC Access Often Fails (The Closed‑PLC Culture)

Many Western equipment manufacturers do not disclose the following PLC information:

Tag names
Meanings of internal variables
Internal logic
Data blocks intended for external output

In other words, you cannot tell what each value actually represents.

Even if an external SIer manages to read the program, there is no guarantee that meaningful data can be extracted.

Additionally, connecting gateways or dataloggers directly to the PLC may interfere with the machine’s control program, creating operational risks.

2. Japanese PLCs Are Built on an “Open” Culture

In contrast, Japanese manufacturers overwhelmingly use Mitsubishi Electric MELSEC PLCs, which typically offer:

Published tag names
Well‑structured external data blocks
Freedom to read and write
Built‑in support for external system integration
Straightforward cloud connectivity

This creates an “open PLC culture” in Japan.

As a result, many Japanese companies naturally assume that “PLC data extraction should be easy.”

3. Why Japanese Companies Struggle with Western Equipment

Western-made equipment, however, often uses PLCs that are closed by design and not intended for external data output.

This cultural difference is one of the main reasons Japanese companies frequently struggle when digitalizing Western equipment.

4. When a Manufacturer Provides a Native Visualization Tool, It Is Usually the Best Option

Some Western equipment manufacturers offer their own visualization or IoT systems.

In such cases, adopting the manufacturer’s native system is usually the smoothest path.

Benefits include:

Accurate interpretation of data
No impact on machine stability
Manufacturer warranty remains intact

5. The Real Challenge: When No Native IoT System Exists

Here is the core issue.

There are many cases where:

The PLC is closed, and
The manufacturer does not provide any IoT or visualization tool.

In these situations, direct PLC access is not feasible, and even if someone can read the program, there is no guarantee that meaningful data can be extracted.

So what should be done?

6. Conclusion: Use the “Dedicated PC” as the Data Hub Instead of the PLC

Almost all Western-made equipment includes a dedicated PC (HMI/SCADA).

This PC typically: