What is Gain/Reset/Rate or modes of operation ?

Gain, reset, and rate conditions are features that determine how quickly the output signal will be changed by a controller. They are also called operating modes and their features have been created with the early pneumatic controllers and vacuum tube controllers and subsequently refined with op amp controllers.

These basic modes of controller response were based on mathematical formulas. These formulas are derived from the calculus functions proportional, integral, and derivative.

The terms gain, reset, and rate originally referred to controller operation. Proportional, integral, and derivative refer to the math functions used to make the gain, reset, and rate actions of the controller.

Gain for Control:

The easiest sort of command to comprehend is called gain, where gain is used by the controller as a multiplier.

The controller uses a mathematical calculation called the algorithm to compute the amount of output for each change of error. This means that the processor is continually checking (sampling) the value from its sensor, which is the process variable (PV), and comparing this value to the set point (SP).

It should be pointed out that the function of the summing junction is performed by a calculation; in older controllers this function was performed by op amps. The formula for error is as follows:

**Error = Set point - Process Variable**

ie., **E = SP - PV**

The error can be a positive number or a negative number, depending on the amount of the values.

From the summing intersection, the controller takes the mistake and utilizes the algorithm to calculate the yield quantity. The algorithm can be a formula complex, but as shown, it can be simplified.

**Output = Gain x Error**

**Mo = Kc x E**

Where, the output is referred to as Mo; the gain is referred to as Kc, which stands for controller (C ) constant (K); and E is error. These terms have become standards for the ISA.