Analog Devices EVAL-AD5934EB Preliminary Technical Data page 12

EVAL-AD5934EB
Now that the frequency sweep parameters and gain settings are
programmed, the next step is to calibrate the AD5934 system by
calculating the gain factor.
The gain factor, which is calculated once at system calibration,
must be calibrated correctly for a particular impedance range
before any subsequent impedance measurement is valid (refer
to the AD5934 data sheet for a more detailed explanation of
gain factor).
The evaluation software can evaluate either a single midpoint
frequency gain factor or multipoint frequency gain factors (that
is, a gain factor for each point in the programmed sweep); see
Arrow 3. The midpoint gain factor is determined at the midpoint
of the programmed sweep; the multipoint gain factors are deter-
mined at each point in the programmed frequency sweep. After
you click Calculate Gain Factor, the software automatically
calculates the gain factor(s) for the subsequent sweep.
Once the midpoint gain factor or the multipoint gain factors
have been calculated, a message is returned to the main dialog
box of the evaluation software (see Figure 15). The gain factor(s)
returned to the evaluation software are subsequently used for
the sweep across the impedance being tested.
Figure 15. Confirmation of a Midpoint Gain Factor Calculation or a
Multipoint Gain Factors Calculation
After the system interface software calculates the gain factor(s)
for the programmed sweep parameters, this value appears in the
Calculated Gain Factor section in the main dialog box of the
evaluation software.
However, it is important to note that if you change any of the
system gain settings (for example, if you change the output
excitation range, PGA gain, etc.) after the system has been
calibrated (that is, after the gain factor(s) have been calculated),
it is necessary to recalculate the gain factor(s) in order to sub-
sequently obtain accurate impedance measurement results. The
gain factor(s) calculated in software are not programmed into the
AD5934 RAM and are only valid when the evaluation software
program is open and running. The gain factor(s) are not retained
in the evaluation software after the software program is closed.
To begin the sweep, click Start Sweep (see Arrow 4). Once the
evaluation software completes the sweep, it automatically returns
both a plot of impedance vs. frequency and a plot of phase vs.
frequency for the impedance being tested (see Figure 14). The
progress of the sweep is outlined with a progress bar, as shown
in Figure 16.
To download the frequency sweep data (that is, frequency,
impedance, phase, real, imaginary, and magnitude data) from
the DFT of the sweep, click Download Impedance Data. The
common dialog box shown in Figure 17 now appears. Choose a
file name in the directory of choice and click Save (see Figure 17).
Note that the default is to save the file in a .csv format.
This saves the sweep data as a comma separated variable file
(.csv) located in the directory of your choice.
You can access this file content by using Notepad or Excel to
plot the data. Each file contains a single column of data. The
format of the downloaded data is shown in Figure 18
Each data entry corresponds to a single measurement (frequency)
point. Therefore, if you program 511 points as the value for the
number of increments, the array contains a single column of
Rev. PrC | Page 12 of 32
Preliminary Technical Data
Figure 16. Sweep Progress Bar (Blue)
1: CHOOSE DIRECTORY
2: CHOOSE FILE NAME
Figure 17. Saving the Sweep Data
Figure 18. Opening the Sweep Data in Excel
3: SAVE THE FILE