SMAR CD600 Plus - Function 12 - Multiplier-Divider-Adder-Subtractor (Arth); Operation

Library of Function Blocks
4.33
Function 12 - Multiplier-Divider-Adder-Subtractor (Arth)
Operation
This block performs the four arithmetic operations with the inputs, as shown by the formula below:
32
2
11
)(
)(
BiasDG
BiasC
BiasBAG
Output ++
+
+
⋅
⋅
=
⋅
Where,
A, B, C and D = inputs (in %)
Bias
1
, Bias
2
and Bias
3
= constants (in %)
G
1
and G
2
= gain (in real numbers)
Output = Result (in %)
Multiplication between a percentage and a real number always results in a percentage. Sum is
always in percentage.
The inputs and the output of this block may range from -102 to +102%. Out of these limits, the
extreme value is taken.
If the input A is not used, the block will assume
A= 100%.
If the inputs B or C are not used, the Bias parameters (ABS1 and ABS2) shall be adjusted to 100%
in order to avoid that G
1
.A(B + Bias
1
)/(C + Bias
2
) be equal to zero in the first case (multiplication by
zero) or always "saturated in 100%" in the second case (division by zero).
EXAMPLE 1: Calculation
100% =
Bias
2
10%; =
Bias
1
30%; = B 20%; = A 2; =
G
1
According to the formula the output should be:
16% =
100
40% x 40%
=
100
10) +(30
20 .2
EXAMPLE 2: Ratio control with fixed ratio constant.
A very important application of Function 12 is the ratio control. See example of configuration
Section 3.
The purpose of this control is to maintain the ratio of flows Q
A
and Q
B
constant:
K =
Q
B
Q
A
The best way to achieve this, is to control one of them, for example Q
B
, with a Setpoint
corresponding to Q
A
/K. Q
B
is called controlled flow and Q
A
wild flow. Figure 4.12.1 shows
configuration to be used.