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APPENDIX D
107
A
PPENDIX
D
C
ALIBRATION
O
VERVIEW
In order to ensure the measurement accuracy, the analog gain and offset must be regularly calibrated.
This is especially true when significant temperature changes occurred since the last time the
instruments was calibrated. With the EMX-4250/51, EMX-4350, and EMX-4380, the user can
perform calibration using internal reference signal. This is called self-calibration. For self-
calibration to work properly, the reference calibration signal should be calibrated annually. This is
called factory-calibration.
S
ELF
-C
ALIBRATION
Self-calibration can be performed without any external equipment or special cabling. It is performed
by the Digitizer or DSA driver’s
Calibration.Self
interface. During the self-calibration, the internal
reference signal is automatically routed to the analog front end and the complete signal path is
calibrated. Once the self-calibration is performed, the calibration constants (
Adjustments
) are
generated in volatile memory and automatically applied during the data acquisition. Self-calibration
constants can be saved or restored to the non-volatile memory using the
SaveAdjustments
and
LoadAdjustments
methods. Otherwise, this information is lost after the instrument is turned off.
Self-calibration is primarily used to calibrate drift due to temperature variations. Self-calibration
can be done with users signal connected to the input connectors.
Analog
AAF
ADC
Gain & Offset
Calibration
Self Calibration
Reference DAC
FIFO
Analog
Input
Range
Selection
Decimation
Filters
Figure D-8-1: Self-Calibration
F
ACTORY
C
ALIBRATION
Factory calibration calibrates the reference signal as well as IEPE current source and charge
amplifier (EMX-4380). Factory calibration constants are stored in non-volatile memory when the
instrument is shipped from VTI or re-calibrated at authorized facilities. Factory calibration constants
are password protected to avoid their being accidental overwritten. These constants are
automatically loaded and applied to the calibration reference signal during the self-calibration.
Optionally, the factory calibration constants can be copied, modified, and stored into a separate non-
volatile memory. It is called full calibration. When the
Full.LoadByDefault
property is set to true,
the full calibration constants are used instead of the factory calibration constants. Calibration
