What is defferent between open loop and closed loop in instrumentation and control field?

Question

What is defferent between open loop and closed loop in instrumentation and control field?

Answer 1

Open loop is system in which the set points are set at a constant value.

A closed loop is a system in which the controller provides information which keeps fluctuating and the set point keeps changing accordingly

Answer 2

Open loop in electronics means that there is no load and for closed loop there is load (that is not a shortcut). But if you are using for instance negative feedback  ( PID controler for instance) open loop means that there is no feedback and for closed loop there is feedback.

Answer 3

Open loop is typically when the critical variables are set at a constant. The system may operate this way until either directed by a human or a program, such as a PLC tells it otherwise.

A closed loop system is where the critical characteristics or variables provide information to the host controller which in turn makes corrections for a given output.

A very good example of a open loop which converts to a closed system is the Air/Fuel mixture of a automobile. Initially when the engine starts the system is in an open loop mode where the Fuel - Air mixture is constant. After a proper temperature, determined by the engine coolant sensor,  is reached the controller converts to a closed loop system. At this point the Controller monitors, Exhaust Gas Temp, Air Intake Temp & Engine Speed to name a few. The engine will run more lean and can produce more Torque as well as save on fuel usage.

Answer 4

Leave out the discussion on load vs. no load and the 1st discussion is fine.

Closed loop utilizes feedback, typically negative and from the output to the input to stabilize the output.  

It can apply to amplitude (sometimes called automatic gain control - AGC) and/or phase (phase locked loop).