InstrumentationProcess Control



Adaptive control is a method whereby the gain of a system can be varied depending on the position of the set point.  The following shows a simple example of why this is useful in control systems.

Figure  shows the level control of a separator.  The level in the separator can be set to control at position A or position B.

As the level changes the volume of liquid to be removed or added at position A is much greater than what must be removed or added at position B.  So, for good response the gain at position A should be greater than the gain at position B.  The LIC is mP based.  The gain of the controller is programmed by the engineer so that it changes when the set point is changed.


Adaptive control is based on the development of a compensating adjustment through knowledge of a disturbing factor or on the basis of loop response itself. A system that adapts itself on the basis of a measurement of a disturbing factor is referred to as programmed system. 

A system that uses a measurement of its own performance is termed self-adaptive. 

On the other hand, self-adaptive systems must sense variations in plant behaviour.This is what identification is  and it is normally a partial measurement  e- cause total identification is either too complex or impossible. After identification, the adaptive device or system must be able to adjust some controller parameter or function. This is referred to as actuation and is illustrated in the schematic diagram of  fig below

In a real sense, programmed adaptive control is feedforward in nature, while self adaptive is feedback.


Increased production rates.

Increased tool life

Highest metal removal rates consistent to the existing conditions.

It is more advantageous where there are wide variations in the depth of cut during machining.

Dimensional accuracy and better surface finish can be obtained.


  • Unavailability of suitable sensors that have a reliable operation ina manufacturing environment.
  • Force and torque sensors in  systems are difficult to install


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