Detailed description

Switching the setpoint

The setpoint can be switched in two directions

If	Then
SP_RSP from 0 → 1	the local setpoint is switched to a remote setpoint
SP_RSP from 1 → 0	the remote setpoint is switched to a local setpoint

SP_RSP from 0 → 1

The changeover from local setpoint to remote setpoint is bumpless: the value of the SP output is increasingly adjusted to correspond to the remote setpoint RSP, and it describes the ramp rate.

If rate rate = 0, there is no ramp and the SP is identical to the RSP.

SP_RSP from 0 → 0

The changeover from remote setpoint to local setpoint depends on the bump element in two ways:

If	Then
bump = 0	the changeover is bumpless: The function block stops copying the RSP input to the SP output. The local setpoint value SP then corresponds to the last remote setpoint value RSP that was present before the changeover. The user can then modify this. In this case it is not necessary to attach the LSP_MEM output.
bump = 1	the value of the LSP_MEM output is moved to the SP output during changeover (bumps can occur here). The value given for LSP_MEM corresponds to the last setpoint value SP before the function block transfers to remote mode. To restart the local mode with a different setpoint, it is sufficient to modify LSP_MEM as long as the block remains in remote mode (for further details see "Function of the output LSP_MEM").

Then

bump = 0

the changeover is bumpless: The function block stops copying the RSP input to the SP output. The local setpoint value SP then corresponds to the last remote setpoint value RSP that was present before the changeover. The user can then modify this. In this case it is not necessary to attach the LSP_MEM output.

bump = 1

the value of the LSP_MEM output is moved to the SP output during changeover (bumps can occur here). The value given for LSP_MEM corresponds to the last setpoint value SP before the function block transfers to remote mode. To restart the local mode with a different setpoint, it is sufficient to modify LSP_MEM as long as the block remains in remote mode (for further details see "Function of the output LSP_MEM").

Tracked setpoint (track = 1)

At local setpoint value (SP_RSP=0), and with the linked controller in manual mode, the PV input can be continuously copied to the setpoint SP value being used. This enables a bumpless changeover from manual to automatic mode (it is also possible for the controller to control the bumpless behavior itself).

In this operating mode, the inputs PV and MA_I of the function block SP_SEL must be attached. You must adopt the same value as the controllers PV input and its outputMA_O. If track = 0, these inputs do not need to be attached.

Limits

In each operating mode (remote or local) the setpoint value SP used is limited to the range between sp_min and sp_max.

Function of the output LSP_MEM

This output enables the user to control the setpoint value SP during a remote – local changeover:

Type of setpoint	Behavior of the output
Local setpoint	The value of SP is continuously moved to LSP_MEM.
Changeover to remote setpoints	The value of LSP_MEM is no longer modified by the function block and therefore retains the value of the last local setpoint used.
Reverting to the local setpoint	There are three possibilities for this: bump = 0: The last remote setpoint value is used as a basis; in this case LSP_MEM does not need to be attached). bump = 1: The last local value saved is used as a basis; during changeover the block copies the value of LSP_MEM onto SP. The function block can start local mode using any value selected by the user. If the value of the variable attached to LSP_MEM before transfer to the local setpoint (with bump = 1) is modified, it is moved to SP during the changeover.

Example of programming

An example of how to program the SP_SEL function block follows.

TC2_SP

is entered by the operator in "local setpoint" operating mode.