Purpose and steps of the regulator’s positive and negative actions

The purpose is to achieve negative feedback for the entire circuit. 1. Positive and negative deviations: In automatic control systems, the parameter being controlled often deviates from its set value due to the influence of disturbances; in other words, a deviation occurs in this parameter: e = pv – sp. Here, e represents the deviation ； pv is the measured value ； sp is a given value. *Conventionally, e>0, which is referred to as a positive deviation ； e

Great post, support it! Once you’ve learned it, just organize it into a mnemonic

It’s very detailed. . . But it’s not easy to remember

In general, for single-acting valves, they remain open or closed depending on the operating conditions when air or power is lost; whereas for double-acting valves, an emergency air tank can be used to ensure they remain open or closed

1) The forward and reverse action of the regulator is set once and for all (provided that the process does not change and the operating mode of the valve being controlled remains unchanged; in the case of pneumatic valves, this means operation based on air pressure to open or close them)； 1) For electric valves, it refers to the way in which the valve opens and closes in response to an increasing signal. 2) The positive/negative action mode of the regulator can be understood as follows (taking positive action as an example): when the measurement signal is greater than the set value, the output of the regulator gradually increases (the regulator’s output is a 4-20mA signal); consequently, the current signal output by the regulator changes. If the control valve used is a air-operated valve, an increase in the current output by the regulator will cause the valve to gradually close ；  If the control valve used is a air-actuated valve, as the current output by the regulator increases, the valve will gradually open. 3) Personally, I think it’s not necessary to memorize the forms of action and reaction; it’s sufficient to understand them based on the manufacturing process during debugging ； After debugging, neither operators nor maintenance staff should make any changes to it. (If the valve needs to be replaced, attention must be paid to whether its mode of operation changes; if it does, the forward and reverse operating mode of the regulator also needs to be changed.)

I finally found you after searching so hard

Study*, learn more! Thank you to the original poster for posting!

Valves for FC generally use reverse action, while those for FO use direct action

Study*, learn more! Very useful!

Reply to 2# zyzs: In a cascade control loop, when selecting the positive or negative action mode for the main loop controller, the secondary loop is treated as a single-loop system with a constant setpoint. How should this be understood? I still can’t determine whether the main loop regulator should operate in positive or negative mode.