Evan G., Jeff K.

Jeff and I got to talking about the problematic 1 Hz comb (and associates) below 100 Hz, and he thought maybe we could have a look at the timing system because there are certainly a lot of 1 PPS signals running around. Our goal was to get a sense of the system and to see where we might start looking for anything broken or misbehaving (not that there is an obvious problem, but it is a place to start).

Summary:

We looked at channels on the timing comparitors to check out timing difference between the GPS signal from the master/fanout with comparitors. The timing fanouts looks very stable aside from a small (~40 ns) shift at EY compared to the EY Symmetricom GPS antenna after a power outage. Another comparitor, the Time Code Converter (TCT), shows a constant, consistent drift at CS, EX, and EY. The timing difference currently for the TCT is around -1.6 us for CS, EX, and EY.

Details:

From the Timing MEDM screens we looked at the comparitor signals to understand the time difference. We had to verify where the cables were plugged in because it is not obvious from the MEDM screen. We used T070173 as a reference for the timing system. We made 60-day trends of the mean values for the different comparison values. Our legends are labeled as follows:

H1:SYS-TIMING_C_MA_A_PORT_2_SLAVE_CFC_TIMEDIFF_1 = "Timing solutions flywheel vs timing master"
H1:SYS-TIMING_C_MA_A_PORT_2_SLAVE_CFC_TIMEDIFF_2 = "Atomic clock? vs timing master"
H1:SYS-TIMING_C_MA_A_PORT_2_SLAVE_CFC_TIMEDIFF_3 = "Symmetricom GPS Antenna vs timing master"
H1:SYS-TIMING_X_FO_A_PORT_9_SLAVE_CFC_TIMEDIFF_1 = "EX Time Code Converter (TCT) vs EX Timing Fanout"
H1:SYS-TIMING_X_FO_A_PORT_9_SLAVE_CFC_TIMEDIFF_3 = "EX Symmetricom GPS Antenna vs EX Timing Fanout"
H1:SYS-TIMING_Y_FO_A_PORT_9_SLAVE_CFC_TIMEDIFF_1 = "EY Time Code Converter (TCT) vs EY Timing Fanout"
H1:SYS-TIMING_Y_FO_A_PORT_9_SLAVE_CFC_TIMEDIFF_3 = "EY Symmetricom GPS Antenna vs EY Timing Fanout"

It appears that things are ok, but we are not sure at what values "we should get worried about this." The only other notable issue was looking at the MEDM screen, the channel H1:SYS-TIMING_C_FO_A_PORT_11_SLAVE_CFC_FREQUENCY_4 would periodically drop to zero and oscillate much more than any of the other channels. We do not know if this is a problem.