# FC 15 - Summer (2 Input)

This function performs a weighted sum of two inputs. By choosing the proper gains and inputs this block can perform proportional, bias or difference functions. It also can be used as a scaler for non-zero based signals by referencing the second input to a constant block.

The following equation describes the operation of this function:

Output = (<S1> X S3) + (<S2> X S4) Outputs:

 Blk Type Description N R Output value is the weighted algebraic sum of the two input signals

Specifications:

 Spec Tune Default Type Range Description S1 N 5 I Note 1 Block address of input #1 S2 N 5 I Note 1 Block address of input #2 S3 Y 1.000 R Full Gain parameter of first input S4 Y 1.000 R Full Gain parameter of second input

NOTES:

1. Maximum values are: 9,998 for the BRC-100, IMMFP11/12 and 31,998 for the HAC

15.1 Applications

Besides performing proportional, bias or difference functions, this code also can be used for scaling. By referencing the second input to a constant block or to a manual set constant block (function code 2), a non-zero based signal can be scaled.

The example in Figure 15-1 shows how to scale an input with a range of 200 to 500 engineering units to give an output of ten to 110 engineering units.

The S3 constant is calculated using the equation: Fixed block four connects to S2 to give it a constant value of -1.0. Specification S2 could be set to any fixed value by using function code 2, but this approach requires more memory than using a fixed block. Since <S2> and S4 are both constants in this example, they can be considered as a unit. The following equation determines the value for the product of <S2> and S4:

<S2> X S4 = Output min. – (<S1> min. X S3 min.)

In this example then:

<S2> X S4 = 10 - [(200)(0.333)] = -56.667

<S2> and S4 could then be set to any allowable value that will give the product of -56.667. In our example, <S2> is set to -1.000 so S4 is set to 56.667. 