After you create an instrument, you can log changes of its value through time with the “Log instrument values” option in the “Instruments and markers” menu.

After you select the “Log instrument values” option from the “Signal tools” menu, you will have to determine the length of the log signal (in samples). A new, empty, signal of the defined length will be created and a new window will appear.

Each time the instrument's value changes, it will be added to the log window; it will work just as an old-fashioned paper-tape recorder.

Scrolling and resetting

The log window will monitor all changes in the instrument and add all consecutive values from the instrument into one signal. When this signal reaches the maximum length you determined, the display will start to scroll, removing oldest values, and adding new ones. By selecting the “Reset data” from the Log windows context menu (or pressing F3), you can clear all values and start logging again. By using the “Start/Stop” options from the context menu, you can stop logging and start it again.

X-axis units

The value log signal will try to automatically determine values for its X-axis by backtracking through the analysis chain to the root signal window. If those X values are equidistant (i.e. the difference between two consecutive values is always the same), those will be displayed on the X-axis of the instrument log. If not, the X-axis will switch to a unit called "change" where each new value will simply be labelled with its index, i.e. 0,1,2,3,4...

Long-time logging of instrument values in a file

Since the instrument log stores its data in your computer's RAM, the total storage length is limited. For long-time recording of signal values, you can use the Logging data to file option connected to a log instrument window. For example, this would be a Control Window display of a system to store max frequency from an FFT into a file.


The instrument log in this system only stores the last 100 values and can be used for monitoring. The file log window, on the other hand, stores all values which are added to an instrument log into a file.

Alarm range

If you set alarm range in your instrument, it will be displayed in the log windows as a red overlay:

For more information, see the Track changes of signal parameters through time How-To section.

To automatically calculate and display the changes of an instrument value in a longer signal, you can also use Instrument values over time function.