National Instruments NI PXIe-6672 - Manual (Page 34)

© National Instruments Corporation 4-1 NI PXIe-6672 User Manual
4
Calibration
This chapter discusses the calibration of the NI PXIe-6672.
Calibration consists of verifying the measurement accuracy of a device
and correcting for any measurement error. The NI PXIe-6672 is factory
calibrated before shipment at approximately 25 °C to the levels indicated
in Appendix A,
Specifications . The associated calibration constants—the
corrections that were needed to meet specifications—are stored in the
onboard nonvolatile memory (EEPROM). The driver software uses these
stored values.
Factory Calibration
The factory calibration of the NI PXIe-6672 involves calculating and
storing four calibration constants. These values control the accuracy of
four features of the device, which are discussed in the following sections.
TCXO Frequency
The TCXO frequency can be varied over a small range. The output
frequency of the TCXO is adjusted using this constant to meet the
specification listed in Appendix A,
Specifications . This calibration
applies only to the NI PXIe-6672.
PXI_CLK10 Phase
When using the PLL to lock PXI_CLK10 to an external reference clock, the
phase between the clocks can be adjusted. The time between rising edges
of PXI_CLK10 and the input clock is minimized using this constant.
DDS Start Trigger Phase
To start the DDS reliably, the DDS start trigger must arrive within a certain
window of time. The phase of the DDS start trigger is controlled by this
constant to meet the setup and hold-time requirements of the DDS.