YOKOGAWA WT500 User Manual page 163

IM 760201-01E
• User-defined functions allow you to determine physical values other than those of the
measurement functions by combining operands. Only power measurement functions
can be assigned to the efficiency equation (see section 5.3 for details). However, by
using user-defined functions, you can create equations consisting of measurement
functions other than power measurement functions to determine ratios other than
efficiency.
On the WT500, user-defined equations can use other user-defined equations with
smaller numbers as operands. For example, the equation for user-defined function
F3 can be set to F1( ) + F2( ). This allows equations that would otherwise exceed 50
characters in length to be computed. This can be accomplished by for example setting
equations in F1 and F2, and then adding or dividing those equations in F3. This feature
is also convenient when defining multiple equations that include common operands.
For example, you can set common operands in F1, and then set F4 as F3( ) divided by
F1( ) and set F5 as F4( ) divided by F1( ). However, if you enter a user-defined equation
with a number that is greater than or equal to its own number, correct results will not be
obtained. For example, if you set user-defined function F3 to F1( ) + F3( ) or to F1( ) + F4( ),
the computed result will be displayed as "-------" (no data) or "Error."
• Operators
The following operators can be used in equations.
Operator Example
+, -, *, / U(E1,OR1) - U(E2,OR1)
ABS ABS(P(E1,ORT) + P(E2,ORT))
SQR SQR(I(E1,OR0))
SQRT SQRT(ABS(I(E1,OR3)))
LOG LOG(U(E1,OR25))
LOG10 LOG10(U(E1,OR25))
EXP EXP(U(E1,OR12))
NEG NEG(U(E1,OR12))
Usable Characters and Maximum String Lengths in Equations
• String Length
Up to 50 characters.
• Usable Character Types
Spaces and all characters that are displayed on the keyboard
• Equation Examples
An equation to determine the rms value of the harmonic components of the voltage
signal of input element 2.
(Total rms voltage value)
SQRT(SQR(U(E1,ORT))−SQR(U(E2,OR1)))
Note
If an operand in an equation is undetermined, the computed result is displayed as "-------" (no
data). This occurs when a delta computation measurement function is in the equation, but delta
computation is turned OFF, or when a measurement function of an element that is not installed
is in the equation.
5.13 Setting User-Defined Functions
Description
Basic arithmetic
Absolute value
Square
Square root
Natural log
Common log
Exponent
Negation
- (Rms value of the fundamental voltage signal)
2
1
2
3
4
5
6
7
8
9
10
11
12
2
13
14
App
Index
5-37