This model is useful to compute the steady state value of a control variable corresponding to some specified setpoint of an output variable, and to reuse it later to perform simulations starting from this steady state condition.

The block has two different behaviours, depending on the value
of the `steadyState` parameter.

When `steadyState = 1`, the `deltaCO` input is
ignored, and the block acts as a standard PI controller with
transfer function Kp*(1+1/sTi) to bring the process variable
connected to the `PV` input at the setpoint value, by acting
on the control variable connected to the `CO` output. The
setpoint value is `SP0` at time zero, and may change by
`deltaSP` from `Tstart` to `Tend`; this can be
useful to bring the process far away from the tentative start
values of the transient without any inconvenience. The control
variable can be biased by `biasCO` to start near the
expected steady state value of `CO`.

When `steadyState = 0`, the `PV` input is ignored,
and the `CO` output is simply the sum of the
`deltaCO` input and of the freezed steady-state output of
the controller.

To perform a steady state computation:

- Set
`steadyState = 1`and suitably tune`Kp`,`Ti`and`biasCO` - Simulate a transient until the desired steady state is achieved.
- Set
`steadyState = 0`and continue the simulation for 0 s - Save the final state of the simulation, which contains the initial steady-state values of all the variables for subsequent transient simulations

To perform experiments starting from a steady state:

- Load a previously saved steady state, to be used as initial state
- Perform the simulation of the desired transient. The
`offsetCO`input value will be automatically added to the previously computed steady state value.

**Revision history:**

*15 Feb 2004*by Francesco Casella:

First release.

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