How to Log Signals in Simulink: Step-by-Step Guide

To log signals in Simulink, right-click the signal line and select Log Selected Signals. Then run the simulation, and the logged data will be available in the Simulink.SimulationOutput object for analysis.

Syntax

In Simulink, logging a signal involves enabling the logging property on the signal line. The main steps are:

• signal.Line: The signal line you want to log.
• signal.LoggingInfo: Property that stores logging settings.
• set_param: Function to programmatically enable logging.
• sim: Function to run the simulation and collect logged data.

Example syntax to enable logging programmatically:

matlab

set_param('model_name/SignalName','DataLogging','on');
out = sim('model_name');
loggedData = out.logsout.getElement('SignalName').Values;

Example

This example shows how to log a signal named Voltage in a Simulink model called simple_circuit. It enables logging, runs the simulation, and extracts the logged data for plotting.

matlab

model = 'simple_circuit';
load_system(model);

% Enable logging on the signal named 'Voltage'
set_param([model '/Voltage'], 'DataLogging', 'on');

% Run the simulation
out = sim(model);

% Extract logged signal data
voltageData = out.logsout.getElement('Voltage').Values;

% Plot the logged signal
plot(voltageData.Time, voltageData.Data);
title('Logged Voltage Signal');
xlabel('Time (s)');
ylabel('Voltage (V)');

Output

A plot window showing the Voltage signal over time after simulation.

Common Pitfalls

Common mistakes when logging signals in Simulink include:

• Not enabling logging on the correct signal line.
• Forgetting to run the simulation after enabling logging.
• Trying to access logged data before simulation finishes.
• Using incorrect signal names when extracting data.

Example of wrong and right ways:

matlab

% Wrong: Trying to get logged data without enabling logging
% out = sim('model');
% data = out.logsout.getElement('Signal').Values; % This will error if logging is off

% Right: Enable logging first
set_param('model/Signal', 'DataLogging', 'on');
out = sim('model');
data = out.logsout.getElement('Signal').Values;

Quick Reference

Action	Command / Step
Enable signal logging	Right-click signal line > Log Selected Signals OR set_param('model/Signal','DataLogging','on')
Run simulation	out = sim('model')
Access logged data	out.logsout.getElement('SignalName').Values
Plot logged data	plot(data.Time, data.Data)

Key Takeaways

Enable logging on the signal line before running the simulation.

Use the simulation output object to access logged signal data.

Always verify the signal name matches when extracting logged data.

Run the simulation after enabling logging to collect data.

Use plots to visualize logged signals for analysis.