Abstract:

I modified LSC_LOCK guardian and OMC_LSC guardian to speed up OMC lock with sideband and TEM00.
I tested new guardian code several times and the modified guardian seems to work well.

Detail:

Recently, it sometimes takes a long to to lock OMC with sideband and carrier.
The reason is following.
1. Sideband power is sometimes lower than the threshould even if upper sideband is resonating to OMC.
2. Transmission power of carrier is sometimes lower than the threshould of OMC lock trigger.
3. Transmission power of carrier changes a lot in time and sometimes becomes lower than the threshould during the power check.
To avoid unnecessary retry of the scan, I modified the gurdian as follows.

LSC_LOCK guardian (LOCKING_OMC_FOR_IAL_WITH_RF state):

The reason why the sideband power at AS was reduced is reduction of sideband buildup inside the PRC, so I normalized threshould by POP90 signals.
In addition, IMC output power also scales sideband power, so I added normalization by IMC output.
Figure 1 shows the modified guardian script.

OMC_LSC guardian (FIND_RESONANCE_FOR_10W):

First, current threshould for OMC lock during OMC scan is 10mW, which is to high for finding TEM00 mode.
So, I reduced the value from 10 to 6 as shown in fig2.

For identifying locked TEM00 is carrier or not, we used the instantanuous value of OMC transmission.
In that case, the process sometimes fails due to the accidential drop of the OMC transmission.
So, I modified the guardian to check the maximum value of OMC trans for 5 seconds and compare it with the threshould.
In addition, carrier power at AS changes in time while the sideband power is relatively stable, so I also implemented the function to check the PV value of OMC transmission power.
Figure 3 and 4 show the guardian script after modification.