When you compare "H1 SNSW EFFECTIVE RANGE (MPC) (TSeries)" data in DMT SenseMonitor_CAL_H1 with its copy in EPICS (H1:CDS-SENSEMON_CAL_SNSW_EFFECTIVE_RANGE_MPC), you will find that the EPICS data is "delayed" from the DMT data by about 109 seconds (109.375 sec in this example, I don't know if it varies with time significantly).
In the attached, vertical lines are minute markers where GPS second is divisible by 60. Bottom is the DMT trend, top is its EPICS copy. In the second attachment you see that this results in the minute trend of this EPICS range data becoming a mixture of DMT trend from 1 minute and 2 minutes ago.
This is harmless most of the time, but if you want to see if e.g. a particular glitch caused the inspiral range to drop, you need to do either a mental math or a real math.
(Out of this 109 seconds, 60 should come from the fact that DMT takes 60 seconds of data to calculate one data point and puts the start time of this 1 min window as the time stamp. Note that this start time is always at the minute boundary where GPS second is divisible by 60. Remaining 49 seconds should be the sum of various latencies on DMT end as well as on the copying mechanism.)
The 109s delay is a little higher than expected, but not to strange. I'm not sure where DMT marks the time, as the start/mid/end of the minute it outputs.
| Start Time | Max End Time | Stage |
| 0 | 60 | Data being calculated in the DMT. |
| 60 | 90 | The DMT to EPICS IOC queries the DMT every 30s. |
| 90 | 91 |
The EDCU should sample it at 16Hz and send to the frame writter. |
The 30s sample rate of the DMT to EPICS IOC is configurable, but was chosen as a good sample rate for a data source that produces data every 60 seconds.
It should also be noted that at least at LHO we do not make an effort to coordinate the sampling time (as far as which seconds in the minute) that happen with the DMT. So the actual delay time may change if the IOC gets restarted.
EDITED TO ADD:
Also, for this channel we record the GPS time that DMT asserts is associated with each sample. That way you should be able to get the offset.
The value is available in H1:CDS-SENSMON_CAL_SNSW_EFFECTIVE_RANGE_MPC_GPS