By choosing System control/Signal calculator option from the main menu or pressing
toolbar button, you can start one of the most useful tools in SIGVIEW, the Signal calculator.
Just as a standard calculator is used for calculating expressions with numbers, SIGVIEW’s
calculator can be used to combine signals or instruments in different arithmetic or signal analysis
expressions. You can use it, for example, to add or subtract two signals or spectrums or to
perform different cross-spectrum calculations.
Usage
In the upper left box, the names of all existing signal or instrument windows (loaded signals, FFT
results, etc.) in your SIGVIEW workspace will be shown. You can choose to display all windows,
only instruments or only signal-like windows (containing sequences of values).
The list box on the right side will contain the new expression for the evaluation.
At the bottom of this dialog, various buttons with all available calculator functions are shown. Only
functions which are available in the given context will be enabled. For example, only after you add
a signal window to your expression, a binary function buttons like "+", "-", "/",... will be enabled.
You can move signals from the left to the right box (include them in the expression) by double-clicking their names or selecting them and pressing the ‘>>’ button. For example, to subtract two
signals, simply select the name of the first one, press ‘>>’ button to add it to the expression, then
press ‘-’ button, and finally add the second signal to your expression.
Important note: Longer arithmetic expressions will be calculated in the order listed in the
expression box and not according to the mathematical operator precedence. For example, the
expression sqrt(A) + log(B) * C will be calculated as (sqrt(A) + log(B)) * C. The expression
A+B*C+D+E*F will be calculated as ((((A+B)*C)+D)+E)*F.
When you create the complete signal expression, click OK to create the result signal. It will be linked to all windows included in the expression
and will recalculate and redraw each time they
change. In case that one of expression windows is deleted, the calculator window will be frozen
and will keep its last values.
Functions
Unary functions (can be applied to a one signal or instrument window)
·sqrt (square root)
·log (log_{10})
·ln (log_{e})
·x^2 (squared)
·abs (absolute value)
·2* (multiply with 2)
·10* (multiply with 10)
·(1/2)* (multiply with 1/2 i.e. divide with 2)
·(1/10)* (multiply with 1/10 i.e. divide with 10)
·sin, cos, tan, atan: trigonometric functions
Binary functions (can be applied to two signal or instrument windows)
If only simple arithmetic binary functions (*, /, +, -) are used, you can freely mix instrument and
signal windows in the expression.
If you include two signals of different lengths in a binary operation (for example you subtract one
signal from another one), SIGVIEW will use only a part of the longer signal (starting from its first
sample) which has the length of the shorter signal.
Examples
Here are some examples of calculator expressions.
1. Simple arithmetic operation on spectrums.
You have loaded two signals, calculated their spectrums and you have the following workspace:
Now, you would like to subtract two calculated spectrums to get some information about their
differences. To do it, create the following expression in the Signal calculator:
The resulting window will contain th requested difference between spectrums.
2. Combining instruments and signals in one expression
You would like to subtract mean value of a signal from all signal values (normalization). First, you
would calculate signal mean by using the appropriate instrument:
Then, you would create the following expression in the Signal calculator:
The result will be a new signal calculated as requested:
2. Instrument-only expressions
You can also have expressions containing only instrument windows. The result of such
expressions will also be a new instrument window.
In this example, we calculate RMS of two signals and then create a new instrument containing
their difference:
3. Complex expressions
There a practically no limitations for creating calculator expressions. Here are some examples:
f = A^2 + abs(B) - B^2
Subtract spectrum of one signal from its cross spectrum with another signal
Calculate log-values of both real and imag spectrum and then perform inverse FFT