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 (onoff).

It is possible to measure Tsys at any time with the command

systemp12

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

tpicd=display_on

and turn it off again with

tpicd=display_off

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:

tpicd

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.