By changing the forward and reverse action of the regulator, doesn’t the negative feedback loop turn into positive feedback?
Thread Content
This post was last edited by wwxxss_1 on 2009-5-26 at 10:56. On-site, I saw the configuration engineer change the forward and reverse action of the regulator; wouldn’t that turn the negative feedback loop into positive feedback? Can it still converge? The personnel on site said that negative feedback can be maintained through internal adjustments in the DCS. . . I’m really confused about how to adjust it ? ? ? If that’s the case, then for the negative feedback in the circuit to be ensured, the product of the three coefficients learned in university must be negative – wouldn’t that mean such a situation isn’t possible? ! ! !
Isn’t the forward and reverse action of the regulator adjusted in the DCS? Analyze the positive and negative effects of the entire circuit, and then we’ll give you an answer! The entire circuit can only operate under negative feedback!
If the control object is determined and the on/off mode of the control valve is fixed, then is the forward/reverse action of the regulator also set and cannot be changed?
Sometimes, in order to ensure consistent operation by the process operators, regardless of whether the valves are operated by air opening or air closing mechanisms, the DCS control interface specifies that an increased output corresponds to opening the valve while a decreased output corresponds to closing it. For air closing valves, the DCS requires an inverted output; therefore, the direction of action also needs to be reversed. The situation you described might be something like this, and for the entire circuit, negative feedback is definitely involved.
The inverted output within the DCS should also fall under the category of components inside the regulator, right? What should the actual forward and reverse actions of a regulator be?
The internal calculation mechanism is definitely negative feedback.
The so-called positive action means that as the input increases, the output increases as well； The reaction reduces the output as the input increases. This is used to coordinate with the reverse action of the on-site control valve.
I’m confused by what was said upstairs, hehe! Hope for a clear explanation
It’s possible that the air-on and air-off settings of the valves on site were also changed; this can also achieve negative feedback. I’ve seen technicians do this before – they change the air-on and air-off settings of the valves on site, and then adjust the forward/reverse action of the regulator in the DCS
What was said on the 4th floor is absolutely correct: in a DCS system, it is generally assumed that an increase in the regulator’s output corresponds to an increase in the opening degree of the valves on site, regardless of whether those valves are designed to close or open when air flows through them. The air-on/air-off option for control valves is a positive/negative output option in the output module. In determining the negative feedback of the entire circuit, control valves are analyzed based on air flow. Changing the positive/negative action of the regulator is done to keep the entire circuit in negative feedback.
What everyone has said is correct; a control system generally consists of four components: the sensing elements and transduction unit, the actuator, the controlled object, and the controller. The forward and reverse action of the controller can be determined based on the ‘three positive and one negative’ and ‘three negative and one positive’ principles. It’s available in the general information; you can check it.