© 2012 Jackson Labs Technologies, Inc. 35
LC_XO GPSDO User Manual
4.5.7 SYNChronization:FEEstimate?
This query returns the Frequency Error Estimate, similar to the Allan Variance using a 1000s
measurement interval and comparing the internal 1PPS to GPS 1PPS offset.
Values less than 1E-012 are below the noise floor, and are not significant.
4.5.8 SYNChronization:LOCKed?
This query returns the lock state (0=OFF, 1=ON) of the PLL controlling the OCXO.
4.5.9 SYNChronization:health?
The SYNChronization:health? query returns a hexadecimal number indicating the system’s
health-status. Error flags are encoded in a binary fashion so that each flag occupies one single bit of
the binary equivalent of the hexadecimal health-status flag.
The following system parameters are monitored and indicated through the health-status indicator.
Individual parameters are ‘ored’ together which results in a single hexadecimal value encoding the
following system status information:
As an example, if the unit is in GPS holdover, and the UTC phase offset is > 250ns then the following
errors would be indicated:
1) UTC phase > 250ns: 0x4
2) GPS in holdover: 0x10
‘Oring’ these values together results in:
0x10 | 0x4 = 0x14
The unit would thus indicate: HEALTH STATUS: 0x14
If the OCXO coarse-DAC is maxed-out at 255 HEALTH STATUS |= 0x1;
If the OCXO coarse-DAC is mined-out at 0 HEALTH STATUS |= 0x2;
If the phase offset to UTC is >250ns HEALTH STATUS |= 0x4;
If the run-time is < 300 seconds HEALTH STATUS |= 0x8;
If the GPS is in holdover > 60s HEALTH STATUS |= 0x10;
If the Frequency Estimate is out of bounds HEALTH STATUS |= 0x20;
If the short-term-drift (ADEV @ 100s) > 100ns HEALTH STATUS |= 0x100;
For the first 3 minutes after a phase-reset, or a coarsedac change: HEALTH STATUS |= 0x200;
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