Process Engineering Division – Instrumentation and Automation Section – Daily Question – Question dated 2020-08-14

The positive and negative feedback of a regulator refer to the relationship between the regulator’s input signal (error) and the direction of change in the output signal. When the difference between the measured value of the regulated parameter and the set value (i.e., the deviation) is greater than zero, the output signal of the corresponding regulator increases; such a regulator is considered a positive-action regulator. If, on the other hand, the regulator’s output signal decreases, then it is a negative-action regulator.

As the input deviation of the regulator increases, its output also increases; this is positive action, while the opposite is negative action.

The positive and negative action of a regulator refers to the relationship between the direction of change in the regulator’s input signal (error) and the direction of change in its output signal

The positive and negative feedback of a regulator refers to the relationship between the direction of change in the regulator’s input signal (error) and the direction of change in its output signal. When the difference between the measured value of the parameter being regulated and the set value (i.e., the deviation) is greater than zero, the output signal of the corresponding regulator increases; such a regulator is known as a positive-action regulator. If, on the other hand, the regulator’s output signal decreases, then it is a negative-action regulator.

This post was last edited by Ku Liang Zhi Le on 2020-8-14 at 15:15. The forward and reverse action of a regulator are as follows: when the deviation input to the regulator increases, if its output increases, it is forward action; if its output decreases, it is reverse action. The proper setting of the regulator’s feedback action is intended to ensure that the control system operates with negative feedback. Regarding the regulator input error, the instrument defines it as: error = measurement – setpoint. It can be concluded that: increased measurement → increased deviation → increased regulator output → positive-action controller ； }The output change of a positive-action regulator is in the same direction as its measured change, and opposite to the given change. Given reduction → increase in deviation → increase in regulator output → positive-action controller ； Increased measurement → increased deviation → reduced regulator output → feedback controller ； }The output change of the feedback regulator is in the opposite direction to its measured change, and in the same direction as the given change. Given reduction → increased deviation → reduced regulator output → feedback controller ； In control system analysis, the controller error is defined as: error = setpoint – measurement; this definition is known as the system definition. Therefore, there are two definitions for the forward and reverse action of a regulator: the definition based on the instruments related to the regulator’s forward and reverse action, and the definition based on the controller’s forward and reverse action system. These two definitions differ by a negative sign. Now some control systems unify these two definitions; for example, Siemens’ PCS7 uses the controller positive and negative action system definition uniformly.

The positive and negative feedback of a regulator refer to the relationship between the regulator’s input signal (error) and the direction of change in the output signal. When the difference between the measured value of the regulated parameter and the set value (i.e., the deviation) is greater than zero, the output signal of the corresponding regulator increases; such a regulator is considered a positive-action regulator. If, on the other hand, the regulator’s output signal decreases, then it is a negative-action regulator.

A regulator is said to be positive acting when an increase (or decrease) in the system output fed back to the regulator’s input results in an increase (or decrease) in the regulator’s output as well； Conversely, it is called a reactive regulator.

The positive and negative feedback of a regulator refer to the relationship between the regulator’s input signal (error) and the direction of change in the output signal. When the difference between the measured value of the regulated parameter and the set value (i.e., the deviation) is greater than zero, the output signal of the corresponding regulator increases; such a regulator is considered a positive-action regulator. If, on the other hand, the regulator’s output signal decreases, then it is a negative-action regulator.

The reverse effect means that the greater the deviation, the smaller the output; while the direct effect means that the greater the deviation, the larger the output! For example, a controller can be used to control the water level: when the water level transmitter detects that the level is deviating (above) the set value, if the controller operates in feedback mode, its output will decrease, the valve will open less, and the amount of water flowing in will be reduced. This way, automatic control can be achieved! Here it is assumed that: the transmitter, control valve, and system are all of positive action

The positive and negative feedback of a regulator refer to the relationship between the regulator’s input signal (error) and the direction of change in the output signal. When the difference between the measured value of the regulated parameter and the set value (i.e., the deviation) is greater than zero, the output signal of the corresponding regulator increases; such a regulator is considered a positive-action regulator. If, on the other hand, the regulator’s output signal decreases, then it is a negative-action regulator.