NI PXI-6653, Руководство пользователя

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© National Instruments Corporation 4-1 NI PXI-6653 User Manual
4
Calibration
This chapter discusses the calibration of the NI 6653.
Calibration consists of verifying the measurement accuracy of a device and
correcting for any measurement error. The NI 6653 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 6653 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,
Specifications .
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
In order 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.