Continous cal is a way of constantly measuring system temperature (Tsys). It is achieved by continuously modulating a noise diode via a 80 Hz square-wave signal from the DBBC. The DBBC detects the return signal, demodulates it, and uses the on/off values to measure Tsys.
The current setup will measure Tsys every 30 seconds during a scan. Output is not shown by default in the scrolling log, but it does go to the log file on the Field System PC, and monit3 will update the values as they are measured.
Note that in continuous cal mode, broadband Tsys values are not reported, just the narrow-band values.
Continuous cal is also used in pointing observations (i.e.
fivept) and SEFD measurements (
It is possible to measure Tsys at any time with the command
This will report Tsys to the scrolling log and update the monit3 display.
Continuous cal is controlled through a daemon called
tpicd and it produces output to the log file when a scan is being recorded (it starts and stops according to the
data_valid command issues from the schedule). You can force tpicd to show individual power measurements in the scrolling log by typing
and turn it off again with
If you have display on and there is a scan being recorded but Tsys is not updating every 30s, then tpicd is NOT running. To make it work, try this:
and wait for the next scan to start.
Here's a copy of the documentation on tpicd
tpicd - tpi (LBA4, Mark III/IV, VLBA, VLBA4, DBBC racks) Syntax: tpicd=cont,cycle tpicd tpicd=stop tpicd=tsys tpicd=display_on tpicd=display_off tpicd=? Response: tpicd/cont,cycle tpicd/detector list Settable parameters: cont Whether to sample continuously or not: no (default) or yes. If no, samplng is stopped and started by the data_valid=... command. cycle Number of centiseconds per cycle, 0 disables sampling. Monitor-only parameters: detector list List of detectors to be sampled, grouped by IF channel as in the tpi, tpical, tpzero, tpgain,and tsys commands. The list is constructed from the VCs selected by the formatter and the IFs that feed them when the tpicd=... command is issued. Comments: The form "tpicd" is used to start the extraction. The form "tpicd=stop" is used to halt it. The form "tpicd=?" returns the current set-up information. If tpicd is being controlled by the data_valid command, it begins and stops sampling and recording data within one second of a request to do so. In other words within one second of the execution of a "data_valid=..." command. The form "tpicd=tsys" can be used only if continuous cal is selected. It will cause the tsys to be calculated from the next set of samples. The number of samples is specified by the cont_cal command. This does not disturb the behavior otherwise. This command controls the tpicd TPI measurement daemon. The remaining comments describe the daemon. The daemon measures the TPI values (Mark III/IV, LBA4, and DBBC racks) and BBC channels gains and IF channel TPI values (VLBA/4 racks). For Mark III/IV, LBA4, and DBBC racks the values appear in the log as "#tpicd#tpi/" entries. For VLBA/4 racks the values appear in the log as "#tpicd#tpgain/" entries. IF TPI values for the VLBA/4 racks are reported in the tpgain records even though they are not gains. If there is a continuous calibration system (cont_cal=on,...), the raw values are reported in "#tpicd#tpcont/" entries and the derived Tsys values are reported in "#tpicd#tsys/" entires every time the number of samples as specified by the cont_cal command has been collected (these Tsys values are only informational and are used internally by the FS for display of Tsys). None of these are normally displayed to the operator; they only go in the log. There are two exceptions to the tpicd output log entries not being displayed to the operator. The first is that if the command "tpicd=display_on" is given, the entries will be displayed until there a "tpicd=display_off" command is given. The second is that continuous calibration is in use, and the "tpicd=tsys" command is given, then averaged tpi, averaged tpical, noise diode temperatures, and derived tsys are all displayed (and logged), respectively, as "tpi/" and "tpical/", "caltemps/", and "tsys/" records (in all cases without "#tpicd#" appended). For IF channels, data is included only in the average "tpi/" records, even though the values are not strictly TPI. The tpicd daemon results the raw and derived results are returned grouped in pairs of: detector mnemonic, value For #tpicd#tpcont/ they are triples: detector mnemonic, tpi, tpical (except for IF detectors which don't have tpical values). The output is collected into lines by IF channel. Detectors that have no IF assigned are displayed first followed by IFs 1-3 (Mark III/IV or LBA4), 1-4 (LBA), and a-d (VLBA/4, DBBC). If the output for an IF would make a long output line, the output is split into more than one line. A time-out or other error on one more devices for a Mark III/IV, LBA, VLBA/4, or DBBC detector will not prevent results from other detectors from being displayed. A negative integer will be shown for each channel that had an error that prevented an actual measurement from being displayed. An overflow value, 65535, is displayed as dollar signs, $$$$$, (for gains an overflow is 255). For Mark III/IV and LBA4 racks the detector mnemonics for the VCs are displayed as hs, where h is the VC number as hex and s is for the detector is use: d (dual for upper/lower), u (upper), l (lower), a digit 3-7 for other detectors or 'x' for unknown.