Tolerance in smart constraints

AVEVA Production Accounting sets the tolerance (=inaccuracy) value of the additional constraints in Smart Constraint.

The tolerance in smart constraint can be defined as Absolute Tolerance + Relative Tolerance (%)*Imbalance of the additional constraint. The default tolerance is zero and it means that the hard constraint is same as the previous version.

But if you define the tolerance value in Smart Constraint, it will change into the soft constraints with the defined tolerance value as same as the measured stream.

For example, you can impose enthalpy balance constraint using Smart Constraint as shown below.

Enthalpy Balance for E3 heat exchanger is like this:

Enthalpy of S8 – Enthalpy of S5 = Enthalpy of S13 – Enthalpy of S14

Because S8 Enthalpy > S5 Enthalpy and S13 Enthalpy > S14 Enthalpy

And Enthalpy of each stream is expressed as (Reconciled Mass Quantity * Specific Enthalpy) of each stream.

You need to define a smart constraint to specify the enthalpy balance for E3.

In the detail dialog box of a constraint, populate the following fields:

• 1: Enter a name for the constraint

• 2: Select the Use Constraint in Reconciliation checkbox.

• 3: Enter a relevant tolerant value for the constraint.

• 4: Enter an equation in this format.

• 5: Click to create the constraint variables and equation.

  

The equation for the specific enthalpy value of the stream shall be defined as Stream(Stream Name;Enthalpy).

And so Stream(S8;RecMassFlowrate)*Stream(S8;Enthalpy): this syntax means - take the enthalpy value from S8 stream after reconciling it.

You need to create the variable for each stream and edit the equation.

So overall constraint equation shall be like this :

(Stream(S8;RecMassFlowrate)*Stream(S8;Enthalpy)-

Stream(S5;RecMassFlowrate)*Stream(S5;Enthalpy))-

(Stream(S13;RecMassFlowrate)*Stream(S13;Enthalpy)-

Stream(S14;RecMassFlowrate)*Stream(S14;Enthalpy))

If the tolerance is zero, the constraint is hard constraint as same as the previous version.

You can set the nonzero tolerance value of the constraint in the new version as shown below (2% relative tolerance) and then the constraint will be soft constraint, same as the measured stream with the nonzero tolerance value.

If you reconcile with this nonzero tolerance constraint, the reconciled balance of the constraint is increased.