Many people have questions about the S2 duty cycle in actuators or electric valves. What does it mean, and why is it defined this way?
1. The Origin of S1, S2, S3, and S6 Duty Cycles
Le S1, S2, S3, and S6 duty cycles originate from electric motor classifications, with a primary focus on thermal balance. The goal is to ensure that the motor does not overheat due to continuous operation.
Definitions of Common Motor Duty Cycles:
S1 (Continuous Duty Cycle): Operates at a constant load for a long enough period to reach thermal equilibrium.
S2 (Short-Time Duty Cycle): Operates under a constant load for a set time, but not long enough to reach thermal equilibrium, then stops to cool down before the next operation.
S3 (Intermittent Periodic Duty Cycle): Operates in repeating cycles of “running under load” and “stopping” with no impact from startup currents on temperature rise.
S6 (Continuous Periodic Duty Cycle): Alternates between loaded running and unloaded running in repeating cycles, but without stopping entirely.
2. S2 Duty Cycle in Actuators (Electric Valves)
Since actuators (electric valves) use electric motors as their drive mechanism, defining the duty cycle is essential to prevent overheating.
According to JB/T 8219-2016 (China’s industrial standard for electric actuators in process control systems), the actuator’s temperature rise must not exceed 60°C.
S2 Duty Cycle Notation in Actuators
S2-75%: Specifies the duty ratio (the percentage of time the actuator motor is powered on while operating the valve).
S2-30min: Specifies the maximum continuous operation time before the actuator must be turned off to cool down.
3. Practical Considerations for Using S2 Duty Actuators
✔ Temperature Affects S2 Duration
If the actual operating temperature is lower than the rated temperature, the S2 duty cycle duration can be extended.
If the actual operating temperature is higher than the rated temperature, the S2 duration must be reduced to prevent overheating.
✔ Load Affects S2 Duration
If the actuator is operating under a lower load than its rated capacity, the duty cycle duration can be extended.
If the actuator is under a higher load, the S2 operation time should be reduced to avoid excessive heating.
Conclusion
Le S2 duty cycle in actuators defines the safe operation time before cooling is required to prevent overheating. When selecting an actuator, consider:
How long it needs to run continuously
The surrounding temperature
The valve’s load requirements
Understanding these factors ensures longer lifespan and reliable performance of electric actuators.
