NOVA technical note #8 1. Case study: how to use cutoff conditions in a FRA frequency scan?

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1 NOVA technical note #8 1 Cutoffs in FRA 1 Case study: how to use cutoff conditions in a FRA frequency scan? One of the FAQ from NOVA users is: Can I use cutoffs during a FRA frequency scan? Using cutoffs The NOVA options can be used to test measured data points for a cutoff condition (see the Cutoff tutorial for more information 2 ). Using cutoffs is quite straightforward for DC measurements (see Figure 1). Figure 1 The Edit Options window can be used to define cutoff conditions 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. Reminders: A cutoff condition can only be defined for a signal that is sampled 3. The cutoff condition must be met in order for the cutoff action to be triggered. 1 This Technical Note requires NOVA 1.5 or later 2 Available from the Help menu tutorials 3 Cutoffs can be defined on any signal available in the Signal Sampler

2 NOVA technical note #8 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 that 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 Step 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 (see Figure 2).

3 NOVA technical note #8 3 Step 2 Adding a Timed procedure in the FRA frequency scan It is possible to add a Timed procedure into the FRA frequency scan that can be used to check for a user-defined cutoff condition after each frequency. Using the commands browser, locate the Timed procedure command, available in the Measurement general group. Drag this command into the procedure editor frame and drop it below the FRA single frequency command, located in the FRA frequency command (see Figure 3). Figure 3 Adding a Timed procedure to the FRA frequency scan command Commands added to the Timed procedure will be executed after each frequency defined in the scan is applied. For a scan with 50 frequencies, the commands in the Timed procedure will be executed 50 times.

4 NOVA technical note #8 4 Step 3 Adding a Record signals command to the Timed procedure With the Timed procedure added to the FRA frequency scan it is now possible to perform a DC measurement after each individual frequency defined in the measurement. 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 Timed procedure. 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 Timed procedure (see Figure 4). Figure 4 Adding the Record signals (> 1 ms) to the Timed procedure

5 NOVA technical note #8 5 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). Figure 5 Changing the duration and the interval time for the Record signals command Since we only want to sample the second signal through the ADC164 in this example, the Signal sampler should also be adjusted (see Figure 6). Figure 6 Adding the External(1).ADC164#1 to the signal sampler

6 NOVA technical note #8 6 After each single frequency defined in the frequency scan, the External(1).ADC164#1 signal and Time will be sampled 10 times, using an interval time of 0.1 s. Plotting of the E 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). Figure 7 It is possible delete the i vs t plot generated by the Record signals command Step 3 Defining the cutoff condition The Timed procedure is now ready to be used in combination with a cutoff condition on the External(1).ADC164#1. 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 NOVA technical note #8 7 Figure 8 Opening the Options editor window for the Record signals (> 1ms) galvanostatic command The Edit Options window will be displayed. Click on the Cutoff tab to show the edit the cutoff conditions (see Figure 9). Figure 9 The Edit Options window Click the Add button to add a cutoff condition. Since we want to stop the complete procedure whenever the External(1).ADC164#1 drops below 0.6 V, a cutoff on this signal should be defined, in the properties frame on the righthand side, as shown in Figure 10.

8 NOVA technical note #8 8 Figure 10 Setting the properties for the Cutoff Note: the Nr. of detections property defines the number of consecutive detections 4 required to trigger the cutoff condition. In this example, this value is set to 1. Click the OK button to close the Edit Options window. The cutoff option will now be added to the Record signal (see Figure 11). Figure 11 The cutoff condition is now added to the Record signals command 4 See the Cutoff tutorial for more information

9 NOVA technical note #8 9 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. 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 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 instrument, 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 E in on the back panel of the instrument. Load the procedure Cutoff in FRA special.nox provided with this technical note. This procedure is identical to the procedure detailed in this case study. However, an additional Autolab Control command has been added to the Timed procedure (see Figure 12). This command is used to set the DAC164 value to 1 V. An Increment parameter command has been added to the FRA frequency scan to decrement the value of the DAC voltage by 50 mv after each repetition. Figure 12 The modified procedure used in to simulate the cutoff condition

10 NOVA technical note #8 10 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 During the measurement, the Autolab display will show values for the impedance measurement and for the DC measurement (see Figure 13). Figure 13 During the measurement, the Autolab display shows values for the impedance measurement and for the DC measurement Since the value of the DAC164 decreases with 50 mv after each frequency, the cutoff condition will be automatically triggered after the 10 th frequency (see Figure 14).

11 NOVA technical note #8 11 During the measurement, the Autolab display will show values for the impedance measurement and for the DC measurement (see Figure 13). Figure 14 The cutoff condition is met after the 10 th frequency in the scan When the cutoff condition is met, the measurement is immediately stopped and a message will be displayed in User log (see Figure 15). Figure 15 A message is displayed in the user log when the cutoff condition is met

12 NOVA technical note #8 12 Tip: in the procedure illustrated in this technical note, the cutoff condition is tested after each frequency. It is possible to move the Timed procedure before the FRA single frequency in the FRA frequency scan to test the cutoff condition before each frequency (see Figure 16). Figure 16 Placing the Timed procedure before the FRA single frequency command changes the sequence of events