A userentered estimate of the cell's impedance. It is used to limit the number of trials required before acquiring the first data point in an impedance spectrum. Before taking the first data point, the EIS software sets up the potentiostat and FRA to measure an impedance equal to Estimated Z and tries to measure the cell's impedance. If the estimate is fairly accurate, the first (or second) attempt to measure the impedance succeeds. If the estimate is poor, the system may take up to five trial readings before it finds the correct settings. It is generally sufficient if Estimated Z is within a factor of 5 of the cell's impedance.
After the first data point, the last measured impedance is used to calculate new measurement settings, so the entered Estimated Z becomes unimportant.
An accurate Estimated Z is more valuable when the initial frequency is low. Remember, 1 mHz is 1000 seconds per cycle. Each impedance reading requires at least three cycles at a given frequency, so five readings to find a range at 1 mHz will take over 4 hours!
The units for Estimated Z are ohms. There is no reason to enter values larger than 1 TΩW (10^{12}Ω or smaller than 0.01 Ω, because these values drive the system settings to their most sensitive and least sensitive settings, respectively.
