Advanced control blocks > Model Predictive Control (MPC) function block

Model Predictive Control function block parameters

The following table lists the system parameters for the MPC function block:

Table: MPC function block parameters

Parameter

Unit

Description

ABNORM_ACTIVE

None

The indication that a block error condition not selected in BAD_MASK (on the function block level) is True (Active), an error condition (at the module level) not selected in MERROR_MASK is True (Active), or a module status not selected in MSTATUS_MASK is True (Active).

BAD_ACTIVE

None

The indication that a block error condition selected in BAD_MASK (at the function block level) is True (Active), an error condition (at the module level) selected in MERROR_MASK is True (Active), or a module status selected in MSTATUS_MASK is True (Active).

BAD_MASK

None

The set of active error conditions that triggers a user-defined Bad condition. The user selects a subset of block error (BLOCK_ERR) conditions in the BAD_MASK parameter. When any of these conditions is True, the BAD_ACTIVE parameter becomes True. When any of the BLOCK_ERR conditions not included in BAD_MASK is True, ABNORM_ACTIVE becomes True.

BKCAL_IN [1–4]

EU of MNPLT

The analog input value and status from another block's BKCAL_OUT output that is used by an upstream block for bumpless transfer. The number of BKCAL_IN parameters corresponds to the number of MNPLT parameters.

BLOCK_ERR

None

The summary of active error conditions associated with the block. The block errors for the MPC function block are:

  • OOS

  • Local Override

  • Configuration Error

  • Simulate Active

  • Input Failure/Bad PV

CNSTR [1–4]

The output units of the connected block

Constrained parameter (input to MPC function block). Is a range within which the output must fall.

CNTRL [1–4]

The output units of the connected block

Controlled parameter (input to MPC function block). Is maintained at a specific value (setpoint) by adjusting the function block's manipulated output.

DSTRB [1–4]

The output units of the connected block

Disturbance inputs (to the MPC function block). The impact of disturbance inputs on controlled and constraint parameters is reduced substantially through the MPC block's adjusting manipulated inputs to compensate for changes in the disturbance inputs.

INSPECT_ACT

None

Indicates if Inspect is enabled and one or more of the limits for the block have been exceeded. The normal value is 0. This parameter is set to 1 if both of the following conditions are True:

  • The Write To Inspect Alarm context menu item was selected from Inspect for this block.

  • With the Current Hour filter selected, Inspect indicates that an abnormal condition exists for Mode, Control, Input, or Variability. (Note that an abnormal condition will only exist for Variability if both the Variability Index and the Standard Deviation have exceeded their defined limits.)

MNPLT [1–4]

The input units of the connected block

Manipulated output (from the MPC function block). A variable that is adjusted either automatically by the MPC block or manually by an operator. The MPC algorithm acts on the manipulated value to maintain the constraints within limits and the controlled parameter values at setpoint.

MODE

None

Parameter used to show and set the block operating state. MODE contains the actual, target, permitted, and normal modes.

SP [1–4]

EU of CNTRL

The operator's setpoint values. The number of SP parameters corresponds to the number of CNTRL parameters.

SP_WRK [1–4]

EU of CNTRL

The working setpoint of the block. The filtered value of the operator setpoint values used in determining control action.

STDEV

Percent of scale

The largest standard deviation calculation for the control parameters over the standard deviation time.

STDEV_CAP

Percent of scale

The estimated capability standard deviation (measurement of short term variation). An estimate of the least standard deviation the process could achieve ideally.

STDEV_TIME

Seconds

The time frame over which STDEV and STDEV_CAP are performed. The default value of zero is good for most processes where the scan rate is no more than approximately 10 times faster than the time to steady state.

If the process is relatively much slower, it is recommended that you enter the approximate time it takes for the process to return to steady state after a change. This ensures that the STDEV and STDEV_CAP calculations accurately consider the actual time constant of the process.