3.
Write a new value for the oscillator DAC value. The range of oscillator control voltage
values is 0 to 65535, with frequency increasing as the value increases. Use a DAC value
of 32768, which is in the middle of the valid range, as a starting point.
a.
Using the same resource handle, set the
DacValue
property to the new DAC value.
b.
Call Save Changes to commit these changes to hardware.
4.
Measure the OCXO frequency following the steps in
Verifying the OCXO Frequency
Accuracy
.
5.
Compare the measured frequency to the target frequency and repeat steps 3 and 4,
adjusting the oscillator DAC value up to increase the frequency and down to decrease the
frequency.
Note
NI recommends that you implement a binary search to determine the
optimal DAC value. This requires going through 16 iterations, with
confirmation that the final DAC value measured crosses over the target
frequency when the DAC value is changed by 1 bit.
6.
Compare the final measured frequency to the specified limits in
Table 3.
on page 3 to
confirm adjustment completed successfully.
7.
If adjustment was successful, commit the calibration values to device memory. If
adjustment was unsuccessful, cancel the external adjustment action; the chassis may be in
need of repair.
a.
Using the resource handle obtained in step 1c, set the
CalExtAction
property to
Commit (or Cancel if adjustment was unsuccessful).
b.
Call Save Changes to commit these changes to hardware.
Reverification
Repeat the
Verification
section to determine the as-left status of the device. If the measured
value is within the low-limit and high-limit range listed in
Table 3.
on page 3, the chassis is
considered to be calibrated and no further adjustment is needed.
Note
If any test fails reverification after performing an adjustment, verify that you
have met the
Test Conditions
before returning your device to NI. Refer to
Where to
Go for Support
for information about support resources or service requests.
Where to Go for Support
The National Instruments website is your complete resource for technical support. At
ni.com/
support
you have access to everything from troubleshooting and application development self-
help resources to email and phone assistance from NI Application Engineers.
National Instruments corporate headquarters is located at 11500 North Mopac Expressway,
Austin, Texas, 78759-3504. National Instruments also has offices located around the world to
help address your support needs. For telephone support in the United States, create your
service request at
ni.com/support
and follow the calling instructions or dial 512 795 8248. For
PXIe-1095 Calibration Procedure
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© National Instruments
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