Introduction To Maths - ABB COMMANDER 1900 Series User Manual

5 ADVANCED CONFIGURATION LEVEL

5.1 Introduction to Maths

Information.
• Four user-configurable maths blocks – can be used independently or cascaded together.
• Each maths block can be configured to perform one of seven functions:
Standard maths block (arithmetic operations) – add, subtract, divide, multiply, high select, low select and
median
Relative humidity (RH) – from wet and dry bulb sensor temperature
Mass flow 1 – calculation of mass flow from volume
Mass flow 2 – calculation of mass flow from differential pressure
High value – holds the maximum value measured on an input variable
Low value – holds the minimum value measured on an input variable
Real time average – averages a continually varying input over a set period of time.
• Inputs can be either variables or constants.
5.1.1 Standard Maths Block
There are four programmable maths blocks. Each maths block can be constructed using four operands and three operators. The
four operands can be configured as process variable inputs, set points, constants or other maths results. The three operators can
be configured for addition, subtraction, multiplication, division, high value selection, low value selection, median (mid-value
selection) or end maths block.
Note. The elements in each equation are calculated sequentially. It is therefore important to enter the elements in the
correct order to obtain the equation required i.e. 2 + 3 x 4 = 20 ≠14. If median is selected as element 2, element 4
automatically becomes median and element 6 automatically becomes end.
The example below shows the construction of a maths block for the following equation:
(PV1 + PV2 + PV3)
Constant 8
Element 1 Element 2
Constant 8
Constant 1
Maths Block 4
Maths Block 1
Median
Input 6
Low Select
Input 1
High Select
Channel 1/2 Output
Channel 1/2 Output
Divide
(cool)
Channel 1/2 Output
Multiply
(heat)
Subtract
Process Variable 4
Process Variable 3
Add
Position F.B. 2
End
Remote S.P. 2
Local S.P. 2
Process Variable 2
Position F.B. 1
Remote S.P. 1
Local S.P. 1
Process Variable 1
None
Operand Operator
Element 3 Element 4
Constant 8
Constant 1
Maths Block 4
Maths Block 1
Median
Input 6
Low Select
Input 1
High Select
Channel 1/2 Output
Channel 1/2 Output
Divide
(cool)
Channel 1/2 Output
Multiply
(heat)
Subtract
Process Variable 4
Process Variable 3
Add
Position F.B. 2
End
Remote S.P. 2
Local S.P. 2
Process Variable 2
Position F.B. 1
Remote S.P. 1
Local S.P. 1
Process Variable 1
None
Operand Operator
Element 5 Element 6
Constant 8
Constant 1
Maths Block 4
Maths Block 1
Median
Input 6
Low Select
Input 1
High Select
Channel 1/2 Output
Channel 1/2 Output
Divide
(cool)
Channel 1/2 Output
Multiply
(heat)
Subtract
Process Variable 4
Process Variable 3
Add
Position F.B. 2
End
Remote S.P. 2
Local S.P. 2
Process Variable 2
Position F.B. 1
Remote S.P. 1
Local S.P. 1
Process Variable 1
None
Operand Operator
• Maths
Element 7
Constant 8
Constant 1
Maths Block 4
Maths Block 1
Input 6
Input 1
Channel 1/2 Output
Channel 1/2 Output
(cool)
Channel 1/2 Output
(heat)
Process Variable 4
Process Variable 3
Position F.B. 2
Remote S.P. 2
Local S.P. 2
Process Variable 2
Position F.B. 1
Remote S.P. 1
Local S.P. 1
Process Variable 1
None
Operand
17