Electrical or electronic system which does not automatically correct any variation to its output is called an open loop system. The function of any electronic system is to automatically regulate the output and keep it within the systems desired input value or “set point”. If the systems input changes for whatever reason, the output of the system must respond accordingly and change itself to reflect the new input value.
Then we can define the main characteristics of an “Open-loop system” as being:
Any open-loop system can be represented as multiple cascaded blocks in series or a single block diagram with an input and output. The block diagram of an open-loop system shows that the signal path from input to output represents a linear path with no feedback loop and for any type of control system the input is given the designation θi and the output θo. Generally, we do not have to manipulate the open-loop block diagram to calculate its actual transfer function. We can just write down the proper relationships or equations from each block diagram, and then calculate the final transfer function from these equations as shown.
The Transfer Function of each block is therefore:
The overall transfer function is given as:
Then the Open-loop Gain is given simply as:
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