Hinds Instruments EXICOR 150AT, User Manual, Page: 48 / 95

Chapter 4: Software Interface
38 Exicor 150AT User Manual
Number of Measurement Averages
A larger number of measurement averages will result in less noise in the
measurement. However a smaller number of measurement averages will decrease
the amount of time required for the scan. If desired, enter a new number into the
Averages field.
Note: Measurement averages is set to 1 (no averaging) automatically
in High Speed mode.
Sensitivity
This control sets the voltage range that is used by the lock-in amplifier for acquiring
the detector signals. In general, low birefringence samples result in small signals on
the lock-in amplifiers and high birefringence samples result in large signals. Using a
lower sensitivity range allows the lock-in to acquire smaller signals with finer
resolution. Using a higher sensitivity range allows the lock-in to measure larger
birefringence.
For low retardation samples, more repeatable measurements can usually be
obtained by setting the sensitivity to
Input V Low . In general, the Input V Low
setting will work well for samples up to 30 nm. If the sample birefringence creates a
signal that is out of the range of the lock-in sensitivity, an error message will be
displayed in the Retardation field of the main window. If this occurs, set the LIA
sensitivity to
Input V High.
Time Constant
The time constant is the internal averaging time that the Signaloc™ lock-in amplifiers
use when acquiring the detector signal. In general, a higher time constant will result
in less noisy measurements but a longer overall measurement time. The opposite is
true for lower time constants. The appropriate value has been set at the factory prior
to shipment and should not need to be changed by the user. If the time constant
must be changed, choose a new value using the drop-down menu and click
Apply .
The time constant is automatically set to the minimum value when High Speed is
active.
Auto-Calibration Settings
The Auto-Calibration feature is used to perform measurement offsets automatically
before and during a sample scan. In order to use auto-calibration, the system needs
to have access to a “no sample” location even while the sample is loaded. This
location should have no sample material or any other obstructions. To access the
Auto-Calibration settings, select
Configuration Auto-Calibration Settings from
the menu bar.