Problem with manual/automatic switching?
Thread Content
When the control system is in operation, manual and automatic switching can be performed as long as the measured value by the regulator equals the set value (i.e., there is no deviation). Dear sea friends, do you think this sentence is correct?
This statement is probably incorrect; theoretically, the measured value can be equal to the given value, but in practice this is impossible； Generally, as long as the measured value is close to the set value, automatic mode can be activated. The software design of some current DCS manufacturers works in such a way: when the control system is in manual mode, the set value continuously tracks the measured value; once you manually adjust the control parameters to your desired level, it’s possible to switch directly to automatic mode
This post was last edited by ROSEHOOD on 2010-8-2 at 20:41. Generally, we first manually adjust the PV to around SP and observe the value of the actuator; if the actuator value is too high or too low, it is necessary to adjust the bypass until the actuator value is around 60&70&, after which automatic mode can be activated, resulting in minimal disturbances. Although there is PV tracking, if automatic mode is used directly and then the SP is adjusted, the swing amplitude of the actuator may become very large, resulting in significant fluctuations in the system.
I think the key is to ensure that no large fluctuations occur during automatic operation before switching to it (for example, the PID settings need to be appropriate)
Modern DCS systems are equipped with SP to track PV values, enabling essentially disturbance-free switching. Without this feature, manual control must be used to stabilize the system for a certain period of time first; thereafter, the SP value is set to match the PV value before switching to automatic mode. The PID parameters need to be adjusted in advance to meet the control requirements, after which they can be fine-tuned based on the variation curves.