User`s manual

2-6 • E2 User’s Manual Supplement: Flexible Combiner 026-1620 Rev 0 09-15-05
left to right.
6. All logical operators (!, NOT, &&, ||) from left to
right.
If you cannot arrange an equation’s operators in a way
that parses them in the order you need (or if you simply
want to remove all doubt), you may use parenthesis to
specify a different order of operator execution. Expres-
sions that are in parenthesis are executed first before any
operators outside of parenthesis are used. For example,
“5+2*3” without parenthesis results in 11 because the
multiplication is executed first before the addition. How-
ever, in the equation “(5+2)*3” the addition is executed
first because it is in parenthesis, resulting in 21.
Equations and operators in parenthesis can themselves
contain other operators and equations in parenthesis. For
example “((5+2)*3)^2” executes the addition first, fol-
lowed by the multiplication, and finally the exponent,
resulting in 441.
2.4 Functions
Equations for most applications can be built using
nothing but inputs, constants, and operators. However, in
some cases it is not always practical or easy to use nothing
but these components (and in some cases, the equation
you’d have to build would exceed the 80-character limit).
Furthermore, you may sometimes need equations to do
more complicated things (such as converting a floating-
point number to an integer or converting a temperature to
dewpoint) that cannot be handled with operators alone.
For these reasons, the Flexible Combiner offers a large
number of functions that can be used in output equations.
A function is essentially a small mathematical formula that
accepts one or more variables as inputs and returns a
numeric result.
In an equation, a function typically takes the form of
the name of the function followed by a set of parenthesis
that contain the value or values the function will use as
inputs. The values inside the parenthesis of a function may
be constants or inputs.
Functions are always evaluated first in an equation
(from left to right, unless parenthesis are used) before
operators are executed.
EXAMPLE EQUATIONS: INPUTS,
CONSTANTS, AND OPERATORS
Equation Description
AI4+60 The value of AI4 plus 60.
!DI1=DI2 The expression DI1=DI2
returns a 1.0 when both
inputs are ON and a 0.0 if
only one or the other is ON.
The “!” at the beginning of
this equation then inverts the
result of that expression. The
final result is a logical XOR
of DI1 and DI2. (Note: this
can be done more elegantly
with the XOR function,
which is explained later in
this section).
(DI1&&DI2)*AI1 Because DI1&&DI2 is in
parenthesis, the logical AND
of DI1 and DI2 is performed
first. The result of this is
multiplied with AI1. This
means the output will be
equal to AI1 (1.0*AI1) when
DI1 and DI2 are both ON,
and zero (0.0*AI1) when one
or both are OFF.
Table 2-8 - Equation Examples: Inputs Using Constants