The MPCPro function block can reference input and output blocks assigned to traditional or HART transmitters and valves. It can also reference blocks assigned to fieldbus devices. All function blocks referenced by the MPCPro function block must contain a scaling parameter. During MPCPro execution, this scaling information is automatically read by the MPCPro block and used in input-output scaling within the block. If an MPCPro block's input references a block that does not contain a scaling parameter such as a math block, a Scaler function block is required. Wire the Scaler function block directly to the upstream function blocksand reference the OUT parameter such that the MPCPro block can access the scaling information.
The engineering unit span configured for measurements associated with control, constraints, or disturbances, directly impact the step response gain. If this gain is less than 0.1 or greater than 20, then it is assumed that the gain is zero and a flat line response will be shown. Thus, if the measurement operating range is small compared to the engineering unit span of the AI block or Scaler block used for the measurement calculation, use the expert options for range suppression in the Test Setup of PredictPro when commissioning the MPCPro block.
For example, if a temperature measurement has an engineering unit span of 1000 degF but the normal operating range is 520-540, a range suppression multiplier of 10X or 100X can be selected. As a result, the calculated step response gain would be processed in a special manner.
Similarly, if small changes in a manipulate parameter have a large impact on Control or Constraint parameters, then specify range suppression in Test Setup.
The function blocks that are referenced by the MPCPro block can be within the same module or in a different module. The Manipulated outputs must reference the CAS_IN, RCAS_IN, or ROUT_IN inputs of the downstream function blocks. If the MPCPro block is being used to replace a PID block, it typically references the CAS_IN or RCAS_IN of an AO block. However, for many other applications, the output of the MPCPro function block can reference the cascade input or remote cascade input of the following function blocks that provides the process input:
Valid parameters and related scales
An MPCPro block can reference the following parameters:
The MPCPro function block treats the downstream process setpoint as the Manipulated process input. As such, the MPCPro function block's Manipulated output is referenced to the CAS_IN of this function block. The BKCAL_OUT and MODE of the downstream block referenced by the MPCPro Manipulated output is automatically read, displayed, and modified if the master switch is toggled between Local and MPC by the MPCPro block based on the path definition for the manipulated parameter.
In some cases, the MPCPro function block replaces an existing control strategy that uses the CAS_IN of the downstream block. You can layer the MPCPro function block on the existing strategy to allow the MPCPro control to be implemented with the old strategy as a backup. You can achieve this by referencing the RCAS_IN and RCAS_OUT (or the ROUT_IN and ROUT_OUT unless referencing an AO block) of the downstream block. The MPCPro function block can reference these parameters in much the same way that it references the CAS_IN of a block.