Answer Posted / magi
Exact positioning of the valve stem
To minimise hysterisis
To linerise a nonlinear system
To use in place where actuator cant produce sufficien force
to move the valve stem
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There are two chlorination tonners both are connected to two pressure swithes and the pressure switch is connected to SOV which operates the valve to changeover the tonner selection i.e if pressure one tonner goes low the other tonner should come in line if it is inautomatic selection design a circuit using relays ?
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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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