Whilst an AC Impedance test is running the time constant of the instrument is altered by switching the potentiostat into a faster mode more suited to an AC Impedance test.
For normal testing Spaced readings should be set on Logarithmic (where the same number of points are collected across each decade) also the Start Frequency should be higher than the Finish Frequency this enables the initial count resistor to be found more quickly.
The Amplitude used for the AC signal plays an important role in obtaining the best possible results always use the highest amplitude possible a test at 30mV AC will yield better results than a test at 4mV AC.
The cell potential applied to the cell is affected by two options firstly is the option Offset test to the rest potential that biases the test around the rest potential if checked the second option allows a DC Offset to be applied (with respect to RE). An example of both options a cell has a rest potential of 133mV if Offset test to the rest potential is checked and there is a DC Offset of 200mV to be applied then the test would be done at 333mV.
Advanced Settings
Each instrument undergoes a very extensive calibration procedure over a series of 8 decades of cell load 10 amplitudes and the full range of frequencies to produce a calibration matrix we call the P.A.I.R. table (Phase and Impedance Reduction). This is then applied to the raw data to reduce cable and instrument induced errors. The PAIR option is on by default it can be accessed on the Advanced options page.
Averaging over a number of points can improve AC Impedance results the averaging options are advanced in that a time penalty of unnecessary averaging is avoided. There are two averaging options which complement each other - Integration factor and Maximum Integration Cycles. Starting with Maximum Integration Cycles this controls the maximum number of averages allowed. The other option Integration factor specifies the percentage error until the result can be passed. For example with a 5% error setting the averaging will continue until the averaged result drift from averaging drift is less than 5%. Low Medium and High translate into 8% 0.75% and 0.25% respectively.
The lower the frequency the longer each point will take to collect at high frequencies many averages can be done in the blink of an eye but at very slow frequencies data collection will slow down dramatically. To speed up a test at these lower frequencies Single Integration Factor below 1 Hz can be checked it effectively turns off averaging below 1 Hz.
Less lower frequency readings can also speed up a test by collecting less points below a certain frequency a percentage of the normal number of points can be set.
