NOVA Technical Note 8 Case study: how to use cutoff conditions in a FRA frequency scan? 1 Using cutoffs Cutoffs in FRA 1 The NOVA options can be used to test measured data points for a cutoff condition. Using cutoffs is quite straightforward for DC measurements (see Figure 1). Figure 1 The Edit Options window can be used to define cutoff conditions Note More information on the use of cutoffs can be found in the dedicated Cutoff tutorial, available from the Help menu in NOVA. On the other hand, FRA measurements in NOVA do not support the use of the Cutoff conditions as such. This technical note illustrates how to implement a cutoff condition during impedance measurements in NOVA by embedding a DC measurement into the FRA frequency scan. 1 This Technical Note applies to NOVA 1.10 or later. 1 Page
NOVA Technical note 8 Reminders: A cutoff condition can only be defined for a signal that is sampled 2. The cutoff condition must be met in order for the cutoff action to be triggered. 2 FRA impedance galvanostatic To illustrate this Case study, the default Autolab FRA impedance galvanostatic procedure will be used on the dummy cell (c) as a starting point (see Figure 2). In this example we assume that a cutoff condition which stops the complete procedure if a second signal, measured on the ADC164, drops below 0.6 V, is required during the FRA measurement. Figure 2 The Autolab FRA impedance galvanostatic procedure 2 Cutoffs can be defined on any signal available in the Signal Sampler. 2 Page
NOVA Technical Note 8 2.1 Defining the DC current This procedure will be used with a DC current of 1 ma. Set the current value of the Set current command to 0.001 (see Figure 3). Figure 3 Defining the DC current 2.2 Adding a Record signals to the FRA frequency scan Since a cutoff option can only be applied on a measured signal, it is necessary to add a Record signals (> 1 ms) command to the frequency scan. This command is used to measure the necessary signals and check for the cutoff condition. Locate the Record signals (> 1 ms) command, available in the Measurement chrono methods group and add it to the FRA frequency scan command, as shown in Figure 4. 3 Page
NOVA Technical note 8 Figure 4 Adding the Record signals (> 1 ms) to the FRA frequency scan For this example, the second signal, measured through the ADC164, needs to be sampled during 1 second, with an interval time of 0.1 s (see Figure 5). 4 Page
NOVA Technical Note 8 Figure 5 Changing the duration and the interval time for the Record signals (> 1 ms) command Since we only want to sample the second signal through the ADC164 in this example, the Signal sampler must also be adjusted (see Figure 6). 5 Page
NOVA Technical note 8 Figure 6 Adding the External(1).External 1 signal to the signal sampler After each single frequency defined in the frequency scan, the External(1).External 1 signal and Time will be sampled 10 times, using an interval time of 0.1 s. Plotting of the i vs t data obtained during this measurement is not required, and the i vs t plot located in the Record signal (> 1 ms) command can be deleted (see Figure 7). 6 Page
NOVA Technical Note 8 Figure 7 It is possible delete the i vs t plot generated by the Record signals command 2.3 Defining the cutoff condition The procedure is now ready to be used in combination with a cutoff condition on the External(1).External 1 signal. As described in the Cutoff tutorial, click the button next to the Options item in the Record signal (> 1 ms) command to open the Edit Options window (see Figure 8). 7 Page
NOVA Technical note 8 Figure 8 Opening the Options editor window for the Record signals (> 1 ms) command Note It is also possible to edit the options by clicking the Record signals (> 1 ms) command and clicking the icon in the quick access toolbar. 8 Page
NOVA Technical Note 8 Figure 9 Editing the options using the quick access toolbar The Edit Options window will be displayed. Click on the Cutoff tab to show the edit the cutoff conditions (see Figure 10). 9 Page
NOVA Technical note 8 Figure 10 The Edit Options window Click the button to add a cutoff condition (see Figure 10). Since we want to stop the complete procedure whenever the External(1).External 1 drops below 0.6 V, a cutoff on this signal should be defined, in the properties frame on the right-hand side, as shown in Figure 11. 10 Page
NOVA Technical Note 8 Figure 11 Setting the properties for the Cutoff Note The Nr. of detections property defines the number of consecutive detections required to trigger the cutoff condition. In this example, this value is set to 1. See the Cutoff tutorial for more information. Click the button to close the Edit Options window. The cutoff option will now be added to the Record signals (> 1 ms) command (see Figure 12). 11 Page
NOVA Technical note 8 Figure 12 The cutoff condition is now added to the Record signals command The procedure is now ready to be used. After each individual frequency measurement, the second signal will be sampled ten consecutive times, using an interval time of 0.1 s. If during this measurement the measured value drops below 0.6 V the whole procedure will be stopped. If the cutoff condition is not met, the measurement will proceed with the next frequency. 3 Testing the procedure on the dummy cell In order to simulate the cutoff condition during the FRA measurement, the procedure provided with this technical note has been slightly adjusted. The cutoff condition is simulated during the FRA frequency scan by changing the value generated by the DAC164. This value will be recorded on the ADC164. To simulate this condition, a special BNC connection must be established: For a PGSTAT fitted with a FRA module, connect a BNC cable between DAC164 #1 and ADC164 #1 on the front panel of the instrument. For a µautolabiii/fra2, connect a BNC cable between the V out and the V in on the back panel of the instrument. 12 Page
NOVA Technical Note 8 For the M101 module installed in a Multi Autolab Cabinet, connect a BNC cable between the V out and the V in connection on the optional monitor cable 3. Load the procedure Cutoff in FRA special [NOVA 1.10].nox provided with this technical note. This procedure is identical to the procedure detailed in this case study. However, an additional Set DAC command has been added to the procedure (see Figure 13). This command is used to set the DAC164 value to given voltage. A calculate signal is used to multiply the frequency index by 50 mv after each repetition. Figure 13 The modified procedure used in to simulate the cutoff condition 3 Contact your Autolab distributor for more information. 13 Page
NOVA Technical note 8 Connect dummy cell (c) and press the start button. The procedure will be started with the following experimental parameters: DC current: 1 ma AC amplitude: 100 µa (rms) Highest frequency: 10 khz Lowest frequency: 0.1 Hz Number of frequencies and distribution: 50, logarithmic Initial value of the DAC164: 1 V Since the value of the DAC164 decreases with 50 mv after each frequency, the cutoff condition will be automatically triggered after the 13 th frequency (see Figure 14). Figure 14 The cutoff condition is met after the 13 th frequency in the scan Note Switch to the analysis view to analyze the measured data points. When the cutoff condition is met, the measurement is immediately stopped and a message will be displayed in User log. 14 Page