Clock offsets and Delays

The fmset program can be used to confirm that the Field system time agrees with the station time. Open a terminal on pcfs[hb|ke|yg], and type

fmset

The Field System and Computer times should agree. Press the <esc> key to exit fmset. Don't leave fmset running for too long!

If fmset if not successful (persistent clock differences), it might be worthwhile to (a) reboot the Mk5, (b) check the DBBC and/or reconfigure/reboot the DBBC.

Now check the maser-GPS and delay through the DBBC and Mark5 (Formatter minus GPS) with the

maserdelay

and

clkoff

commands respectively which read the Agilent counters. Log these values in the checklist. They should be the same to within 0.5 microsec. The Log Monitor should report the difference which should be less than +/- 0.5 us.

Issue the maserdelay and clkoff commands a few times to check that they aren't drifting. A drift in the formatter-GPS time is usually an indication of a DBBC problem, usually requiring a reconfig to fix.

If one or both counters are not responding to these commands, you will see an error message like this

ERROR sp   -4 GPIB Device time-out on response c2

To fix this, try re-setting the counters. In the Operator Input window, type

counter

and try the maserdelay and clkoff commands again.

Be sure that mk5=dot? returns FHG_off before you run fmset. Sometimes if a power glitch occurs while the Mark5 is recording, it can get stuck. If FHG_on, end with disk_record=off and then run fmset again

During the observation, it is useful to monitor the delay difference on a plot. to do it, you can start a terminal on ops8 (or ops1hb at MtPleasant) and run

there is now a live update available (no need to export and re-plot the data). From this, open a terminal on ops8 and type

delaylive hb (ke, yg, ho)

This will pop up a live plot of the delay difference based on readings from the FS log at each site.

If the GPIB has been restarted (via the PDU internet power switch, or a power outage) a field system restart is probably required to re-establish communications with the counters connected to the GPIB. Symptomatic is fmset working OK, sync_error=0, but counter, clkoff, maserdelay commands not working; the ddiff counter showing random large offsets and/or changing rapidly. Restarting the field system should bring the ddiff counter back to a steady several microseconds and enable GPIB comms.