© National Instruments
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4-1
4
Calibration
This chapter discusses the calibration of the NI PXI-665
x
.
Calibration consists of verifying the measurement accuracy of a device and correcting for any
measurement error. The NI PXI-665
x
is factory calibrated before shipment at approximately
25 °C to the levels indicated in Appendix A,
. 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 PXI-665
x
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.
OCXO Frequency
The OCXO frequency can be varied over a small range. The output frequency of the OCXO is
adjusted using this constant to meet the specification listed in Appendix A,
. This
calibration applies only to the NI PXI-6653.
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,
. This
calibration applies only to the NI PXI-6652.
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.
