In industrial automation control systems, 24V DC power supply has almost become the default configuration for PLC systems. Whether it is PLC cpus, digital I/O modules, or on-site sensors and actuators, 24V DC power is widely applied. So, why do most industrial PLC systems choose 24V DC instead of other voltages?
What is 24V DC? What role does it play in the PLC system?
24V DC refers to a 24-volt direct current voltage and is mainly used in PLC systems for:
Power supply for the PLC body and expansion modules
Digital input/output signal power supply
Power supply for industrial sensors (proximity switches, photoelectric switches, etc.)
Control relays, solenoid valves and other actuating mechanisms
In control systems, 24V DC is usually converted from alternating current by industrial switching power supplies (SMPS), forming a stable and controllable control power supply system.
Why do industrial PLCS choose 24V DC instead of AC power?
1. Direct current is more stable and suitable for electronic control systems
The core of a PLC is composed of a microprocessor, logic chips and electronic components, which are naturally more suitable for working in a low-voltage DC environment. Compared with alternating current, 24V DC does not have the problems of frequency fluctuation and zero-point crossing, and the signal is more stable, which is helpful for:
Improve the accuracy of logical judgment
Reduce false triggering and signal jitter
Enhance the reliability of high-speed input and counting functions
The high safety of 24V DC is a key advantage in industrial sites
The industrial site environment is complex, and maintenance and debugging are frequent. Therefore, the safety voltage level is particularly important.
The safety advantages of 24V DC include:
It falls within the range of safe low voltage (SELV)
The risk of human contact is low
Suitable for control cabinets, field terminals and manual operation circuits
This is also an important reason why almost all buttons, emergency stop circuits and signal acquisition adopt 24V DC.
24V DC is highly compatible with industrial sensors and actuators
At present, the mainstream industrial equipment basically uses 24V DC as the standard power supply voltage, including:
Proximity switches, photoelectric sensors
Pressure, liquid level and temperature transmitters
Encoder, limit switch
Solenoid valve and relay module
Unifying the voltage level can significantly reduce the difficulty of PLC system integration, improve equipment compatibility and maintainability.
From the perspective of anti-interference, 24V DC is more suitable for industrial environments
There are a large number of interference sources in industrial sites, such as
Frequency converters and high-power motors
Inductive loads start and stop frequently
High-frequency switchgear
The 24V DC signal performs more stably in terms of anti-electromagnetic interference. Combined with reasonable wiring and grounding, it can effectively reduce signal misjudgment and system failure rates.
The reasons why 24V DC has become the standard for industrial automation
1. Industry standards are highly unified
24V DC has been widely adopted by the global automation industry and has become a de facto standard, making:
PLCS of different brands are easy to integrate
The I/O module has strong versatility with field devices
System expansion and upgrade are simpler
2. Support modular and distributed control
Most distributed I/O, remote sites and fieldbus systems are powered by 24V DC, making the control system more flexible and scalable.
The advantages of 24V DC in terms of cost and maintenance
From the perspective of long-term operation, the 24V DC system has obvious economic advantages:
The supply of industrial power supplies, modules and accessories is sufficient
The wire diameter is smaller, saving materials and space
Fault location is simple and maintenance personnel are highly familiar with it
High power supply efficiency, low heat generation and long service life
These advantages effectively reduce the overall cost of ownership of the PLC system.
Why don't PLCS choose 12V or 48V?
In the field of industrial control, voltage selection needs to balance multiple factors:
12V DC: Short transmission distance, significant voltage drop, and limited driving capacity
48V DC: The safety level has decreased, and the costs of insulation and protection have increased
In contrast, 24V DC strikes the best balance among safety, driving capability and transmission stability, thus becoming the preferred voltage for industrial control systems.
The advantages of 24V DC for global projects and cross-regional applications
Through industrial switching power supplies, alternating current (110V / 230V) from different regions can all be converted to 24V DC, which enables:
The PLC system does not need to be redesigned due to regional differences
Industrial equipment is easier to deploy globally
The replicability and standardization of the project are higher
Conclusion: Why is 24V DC the best choice for PLC systems?
Overall, 24V DC has become the core control voltage standard for industrial PLC systems. The main reasons include:
Safe and reliable, suitable for industrial sites
Highly compatible with sensors and actuators
The signal is stable and has strong anti-interference ability
It is conducive to standardized and modular design
Cost is controllable and maintenance is convenient
Globally applicable and with mature engineering experience
For this reason, 24V DC will remain an irreplaceable basic voltage in industrial automation control systems for a long time to come.
1 Year Warranty
