Answer / himanshu apte

As i understand the question, If 'D' value in PID is
changed, the process responds to the rate of change of
error between the PV & SP. In operation, controller first
compares current PV with the last PV value. If there is a
change in slope of PV, controller determines the output at
a future point in time. This future point in time
represents the derivative setting. Derivative mode
increases the output by that amount.
Advantage: Rapid o/p reduces time required to bring PV to
SP.
Disadvantage: Dramatically amplifies noise signals & can
cause cycling in fast process.

Answer / swatihendre

If D increased then output response will be fast and if D
decreased then output response will slow

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Q1: Consider part of a control loop, which excludes the transmitter, consisting of a process, a controller and a control valve which may be represented by two dead times of 0.5 min each and three exponential lags of 0.8 min., 1.0 min. and 1.5 min. respectively. We wish to express this system as an overall first order plus dead time (FOPLD) model ie gain, time constant and process dead time. (We will see later that this is often done, to simplify controller tuning). For this exercise, gain is considered to be 1.0. (A) If the transmitter is a flow transmitter whose behaviour can be described by a dead time of 0.2 min. and an exponential lag of 0.5 min. in terms of the overall dead time and overall first order lag how can the system behaviour be approximated ? Overall dead time = Overall time constant = (B) If the transmitter is a temperature transmitter with a temperature sensor in a protecting well whose behaviour can be described by a dead time of 0.7 min. and an exponential lag of 15 min. how can the overall system behaviour be approximated now? Overall dead time = Overall time constant =

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