Symmetricom 5115A, Руководство по эксплуатации и обслуживанию

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72 8: Optional Functionality
8.1 5120A-01 Internal Reference
The 5120A-01 features two internal reference oscillators that can be used instead of an external
reference signal when such a signal is not available or required for accuracy. The 5120A-01
automatically switches to internal reference mode when an external reference signal is absent.
8.1.1 5120A-01 Internal Reference Calibration
The 5120A-01 is calibrated before it is shipped from the factory. The frequency of the internal
oscillators must be measured and calibration values entered annually. See section 8.2.1.1 for
details on performing the calibration.
Internal reference calibration must also be performed in the unlikely event of calibration data
corruption. Corrupt calibration data is reflected as an
UNCALIBRATED reference frequency on
the frequency counter screen (when internal reference mode is used), and not calibrated in the
Current Calibration frame of the Internal Reference ( Figure 18 ).
Internal reference calibration can be done on-site provided a calibration lab quality 10 MHz signal
is available. To perform calibration, this signal is attached to Input port on the front panel. Data is
collected in internal reference mode until the 1000 second frequency average has been computed
by the frequency counter. The frequency average is then used to calculate the internal oscillators'
frequencies. For calibration purposes the function of the Input port is thus reversed - it actually
serves as a reference signal used to measure the internal reference oscillators' frequencies.
Upon calibration, the newly determined frequencies are used immediately, even during the data
collection used to perform calibration in the first place. Frequency averages presented by the
frequency counter can be re-examined (without stopping data collection) to study the impact of
calibration.
8.1.1.1 Calibrating 5120A-01 Internal Reference
Internal reference calibration is performed using the Internal Reference screen shown in Figure 18 .
Figure 18: Example Internal Reference Option Screen
Calibration data from
previous, active calibration
Press to calibrate internal
references, once
Pending
Calibration frame indicates
internal reference frequencies
can be calculated.
Displays calibration data to
be stored when
Calibrate soft
key is pressed, or reason why
internal reference frequencies
cannot be calibrated at this
time.