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Open loop vs closed loop instrumentation

Short answer

Open-loop systems operate without feedback, so accuracy depends on component calibration and disturbances are not corrected. Closed-loop systems measure output with a sensor, feed it back to compare with setpoint, and the microprocessor corrects error for high accuracy, but require sensor, ADC, and control algorithm, increasing complexity.

Differentiate between open loop and closed loop instrumentation system along with block diagrams.

An open loop system produces its output from the input command only, without checking the result. A closed loop system measures the output with a sensor and feeds it back to the microprocessor, which corrects the control action to reduce the error.

Open loop MBI

 Set value -> [ Microprocessor ] -> [DAC/driver] -> [Actuator] -> Process

Closed loop MBI

 Set value ->(+)-> [Microprocessor] -> [DAC/driver] -> [Actuator] -> Process
              ^ -                                                    |
              |                                                      |
              +------ [ADC] <- [Signal conditioner] <- [Sensor] <----+
PointOpen loopClosed loop
FeedbackNoneOutput is measured and fed back
AccuracyDepends on calibration of componentsHigh, error is corrected
Effect of disturbanceNot correctedCorrected automatically
Complexity and costSimple and cheapNeeds sensor, ADC, algorithm; costly
StabilityNo stability problemMay oscillate if badly tuned
ExampleWashing machine timer, traffic lightOven temperature control, motor speed control

✓ Answer checked by Claude Sonnet 5.5

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