مدونة

What exactly is 24-volt direct current in industrial automation?

In industrial control systems, 24-volt direct current (24-volt DC) is the main control power supply for PLC, sensors, relays, and communication modules. Unlike high-voltage alternating current used in motors and heavy machinery, 24-volt DC is specifically used for control circuits and signal-level equipment.

Major automation companies such as ABB, Siemens, and Schneider Electric have uniformly adopted the 24-volt DC standard in their PLC platforms and field equipment. This consistency enables seamless integration of controllers, I/O modules, and industrial instruments.

In simple terms, 24-volt DC is the "control heartbeat" that powers modern PLC-based automation systems.

Why has 24-volt DC become the industry standard? 

1. Enhanced safety

24-volt DC voltage is within the low-voltage safety range defined by international electrical standards. Compared to 110-volt or 220-volt alternating current, it significantly reduces the risk of electric shock during installation and maintenance.

2. Strong noise resistance

Industrial environments are filled with electrical noise generated by motors, variable frequency drives, and switch devices. DC systems have greater stability in signal transmission, which helps PLC input and output modules operate reliably.

3. Global component compatibility

Since 24-volt DC has been widely adopted, manufacturers' products (including sensors, solenoid valves, safety relays, and communication modules) are designed based on this voltage. This makes global procurement and replacement more convenient.

4. Simpler backup integration

24V DC power can be directly connected to battery systems and uninterruptible power supply equipment, ensuring that the PLC system can continue to operate during short power outages - which is crucial for process industries and continuous production lines.

Where is 24-volt DC used in PLC systems?

24-volt DC is widely used in:

Central processor power input of PLCs

Digital input and output modules

Proximity sensors and photoelectric sensors

Safety relays and interlock systems

Industrial human-machine interfaces

Distributed input/output systems

When did 24-volt DC replace higher AC control voltages?

In early industrial control systems, panel-based relays typically used 110-volt AC. However, with the development of PLC technology in the late 20th century, electronic components required a lower and more stable voltage.

In the 1980s and 1990s, as semiconductor-based controllers became dominant, 24-volt DC gradually replaced AC control voltages due to improvements in safety, compatibility, and reliability. Today, almost all modern PLC architectures are designed based on this low-voltage DC standard.

Why is 24-volt DC more advantageous?

Reducing electrical risks

Lower voltage can reduce the risk of arc flash and improve workplace safety.

Higher energy efficiency

Low-voltage DC systems generate less heat inside the control cabinet.

Simplified wiring design

Compared to AC systems, technicians can more easily wire and troubleshoot 24-volt DC circuits.

Seamless electronic integration

Microprocessors, communication modules, and intelligent sensors have been optimized for operation at DC voltages.

These technical advantages directly contribute to improving system uptime and reducing maintenance costs.

Who are the biggest beneficiaries of 24-volt DC standardization?

Original equipment manufacturers - simplifying product design for the global market

System integrators - accelerating engineering and commissioning speed

Maintenance engineers - safer and more convenient diagnosis Factory operators - reducing downtime and ensuring stable performance

For global automation component suppliers and industrial service providers, the standardized 24V DC system also means more efficient inventory management and faster support for international customers.

How does 24V DC strengthen modern industrial control systems?

24V DC enhances overall automation performance in the following ways:

Providing stable control signals

Reducing the impact of electromagnetic interference

Supporting redundant power configurations

Achieving modular system expansion

Improving the long-term reliability of equipment

In the modern Industry 4.0 environment, PLC systems are integrated with intelligent sensors, remote I/O, and industrial networks, and 24V DC continuously provides the stable power foundation required for intelligent manufacturing. 

A 24-volt direct current voltage is not merely a common voltage choice – it is a global standard for ensuring the safe and reliable operation of modern PLC systems. Its balance in terms of safety, compatibility, efficiency and performance makes it indispensable in the field of industrial automation.

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