Introducing LabSim: A signal generator to simplify troubleshooting
by Clara Guenter, M.Sc.
Scientific Consultant (Brain Products)
LabSim in a nutshell
LabSim (available from January 2020) is a small and handy signal generator, able to generate signals required to test the input ports of different amplifiers. With the LabSim, it is possible to test an amplifier’s EEG, AUX, and trigger connectors as well as functionality of the complete signal pipeline including electrodes and amplifier.
This signal generator is intended to serve two main purposes: (1) simplification of troubleshooting by using a reliable signal source, and (2) inspection of signal pathways, e.g. in preparation of a large-scale study or as a regular checkup in large labs.
The ability to test these connectors without additional equipment, such as secondary electrode bundles or sensors, allows for more precise and efficient troubleshooting. As identification of malfunctioning equipment is simplified, affected products can be sent for repair without lengthy remote troubleshooting. This way, down time is decreased.
The LabSim is compatible with most of our amplifier families. actiCHamp, BrainAmp, V-Amp, LiveAmp Sensor and Trigger Extension and TriggerBox are amongst the compatible devices.
Figure 1: LabSim device, including connectors for EEG, AUX, 1-bit and 8-bit trigger.
Signal pipeline: Where does LabSim come in?
When recording bioelectric signals, a sequence of stages is passed before the signal is eventually displayed in BrainVision Recorder and saved on a computer. This results in several potential sources of errors. Narrowing down these sources enables us to increase efficiency in the troubleshooting process.
In a typical experiment, a subject is fitted with an electrode cap and the electrodes are gelled. An amplifier is used to amplify and digitize the electrical signal recorded at the electrodes. Finally, the digital signal is passed to BrainVision Recorder on a computer (see Figure 2).
Figure 2: Signal pipeline in an experiment. Subject wears electrode cap with electrodes that are connected to the amplifier. At this point, the signal is digitized and forwarded to BrainVision Recorder.
In case you, the researcher, encounter erroneous data, such as a flat or noisy channel, there are multiple potential sources. Such issues can occur due to a range of reasons such as insufficiently gelled electrodes, dried gel residues, a damaged electrode, or a damaged amplifier channel. A first common troubleshooting step is to take the subject and gel out of the equation by doing a saline test (see Figure 3). Using this test, electrode impedances can be checked. For active electrodes used with actiCHamp amplifiers and actiCAP ControlBox, it is also possible to evaluate the electrodes with a test signal. For many other configurations, however, this is not an option. In a best-case scenario, a second electrode bundle or a second amplifier is available and, by exchanging bundles, the “culprit” can be identified.
Figure 3: Signal pipeline in a saline test. The electrode bundle is submerged in a saline solution, reducing impedances to a minimum. The electrodes are connected to an amplifier that digitizes the signal and forwards it to BrainVision Recorder.
However, many researchers do not have this option, which means the amplifier as well as electrode bundles would have to be sent for inspection and repair. And this is exactly where the LabSim comes in: Using the LabSim, it is possible to check the function of many of our amplifiers. Either by testing the complete signal pipeline by recording the LabSim’s signal with electrodes in a saline bath (see Figure 3), or by connecting the LabSim directly to the amplifier (see Figure 4). Using these two tests with the LabSim, an identification of damaged hardware by exclusion is possible.
Figure 4: Signal pipeline in a test scenario with the LabSim. Electrodes are excluded from the signal pipeline, enabling the experimenter to evaluate the amplifier individually. The test signal generated by the LabSim is digitized by the amplifier and forwarded to BrainVision Recorder.
Similarly, AUX and trigger connectors can be tested. For AUX connectors, appropriateness of positive and negative supply voltage is indicated by two LEDs and function of the signal input can be evaluated. Further, the LabSim generates a 1-bit and 8-bit trigger signal, allowing for examination of different trigger ports.
Parts and accessories
LabSim is a standalone device that can to a large extent be used with available accessories, such as trigger cables delivered with each amplifier. An adapter for actiCHamp and BrainAmp families is available to connect directly to the amplifiers (see Figure 5).
Figure 5: LabSim adapter for actiCHamp and BrainAmp amplifier families.
Conclusion
LabSim is an effective tool to decrease time spent troubleshooting and, as a consequence, decrease downtime due to unidentified errors. LabSim can be used to inspect our amplifiers, before starting a large study or in between study days to confirm the equipment is in a good condition. These regular checks can prevent data loss due to unpredicted occurrences.