Latest update: 2006/01/19

NOTE: For database update info/version number, see section near the end.

General explanation, regular limits

  • On the strings, there are mnemonics called e.g. LIMIT_SWITCH, CDS_SWITCH, UVCS_SWITCH, etc, in addition to the normal housekeeping mnemonics. The value of these mnemonics (which can be thought of as global variables) are used to determine which limit definitions are to be applied at any given time. In the database, each limit defined includes the name of a Switch Mnemonic, and a range for that mnemonic.


    CDS_SWITCH equal to 1 on the string means the string is supposed to use all mnemonic limits defined with Switch Mnemonic "CDS_SWITCH" and a range that includes 1. In general: A LIMIT DEFINITION IS IN EFFECT IF AND ONLY IF THE STRING'S VALUE FOR THE SWITCH MNEMONIC IS WITHIN THE SWITCH MNEMONIC RANGE.

  • The Switch Mnemonic column contains either LIMIT_SWITCH, [INSTRUMENT]_SWITCH, or a housekeeping mnemonic. There is a range column where (typically) both numbers are the same for low and high - either 1 or 2 or 3. This is referred to as the "SWITCH MNEMONIC RANGE".

    LIMIT_SWITCH with a range of 1 to 1 means nominal limits for the team.

    LIMIT_SWITCH with a range of 2 to 2 is never used - these limtis were defined early in the mission and aren't used because it is an all-or-nothing thing. Instead, the [INSTRUMENT]_SWITCH was created.

    [INSTRUMENT]_SWITCH with a range of 1 to 1 are nominal limits for that instrument.

    [INSTRUMENT]_SWITCH with a range of 2 to 2 are ESR limits. If we go into ESR, the FOT switch to ESR limits for CDS, LASCO, UVCS (only if they are on the ESR warning flag receipt list) in the ESR Initial Operations Script CS-06B. SWAN will soon have ESR limits as well.

    [INSTRUMENT]_SWITCH with a range of 3 to 3 are door closed limits.

  • In the future, there may be definitions with ranges covering more than one value (e.g. limits to be used when doors are closed *and* during ESRs).
  • There should never be an [INSTRUMENT]_SWITCH with a range of 1 and 1 and also a LIMIT_SWITCH with a range of 1 and 1 for the same mnemonic - that would mean two limits are defined for the nominal situation. However, an instrument can have some mnemonics be LIMIT_SWITCH with a range of 1 and 1 and others [INSTRUMENT]_SWITCH with a range of 1 and 1 and both are used for nominal limits.
  • Sometimes (SUMER for example), limits are automatically switched by the ranges of a housekeeping mnemonic - this is by instrument design and the FOT have nothing to do with this (they cannot control which limits are in effect).


  • Let's say we have the following limit definitions (abbreviated form of the table, actual limits taken out) for the imaginary instrument "INS":

    ------------Switch----Switch Mnem.

    Mnemonic---Mnemonic---Range Lo/Hi---Limits

    IIVMCPPP---INS_SWITCH ----1/1-------[IIVMCP nominal limits]

    IIVMCP-----INS_SWITCH-----2/2-------[IIVMCP ESR limits]

    IIVMCP-----INS_SWITCH-----3/3-------[IIVMCP Door Closed limits]

    IIVMCP-----INS_SWITCH-----4/4-------[IIVMCP Special Limits 1]

    IIP--------INS_SWITCH-----1/1-------[IIP nominal limits]

    IXMP-------LIMIT_SWITCH---1/1-------[IXMP nominal limits]

    IXMP-------LIMIT_SWITCH---2/2-------[IXMP never used limits]

    IISSMP-----IXSTAT---------0/100-----[IISSMP limits for 0 < IXSTAT < 100]

    IISSMP-----IXSTAT---------101/255---[IISSMP limits for 101 < IXSTAT < 255]

  • So if INS_SWITCH has a value of 1, LIMIT_SWITCH has a value of 1, and IXSTAT (a housekeeping mnemonic defined in telemetry from INS) has a value of 50, the following limits are checked by the string:

    IIVMCP---INS_SWITCH-----1/1-----[IIVMCP nominal limits]

    IIP------INS_SWITCH-----1/1-----[IIP nominal limits]

    IXMP-----LIMIT_SWITCH---1/1-----[IXMP nominal limits]

    IISSMP---IXSTAT---------0/100---[IISSMP limits for 0 < IXSTAT < 100]

  • If the value of INS_SWITCH on the string is changed by the FOT to 3, the following limits will be checked:

    IIVMCP---INS_SWITCH-----3/3-----[IIVMCP Door Closed limits]

    IXMP-----LIMIT_SWITCH---1/1-----[IXMP nominal limits]

    IISSMP---IXSTAT---------0/100---[IISSMP limits for 0 < IXSTAT < 100]

    NOTE: that IIP has no limits defined for any other values of INS_SWITCH than 1, which is perfectly ok as long as the instrument team is aware that the mnemonic is not monitored at all if a non-nominal limit set is applied

  • If the housekeeping mnemonic IXSTAT then changes to a value of 200, the following limits will be applied:

    IIVMCP---INS_SWITCH-----3/3-------[IIVMCP Door Closed limits]

    IXMP-----LIMIT_SWITCH---1/1-------[IXMP nominal limits]

    IISSMP---IXSTAT---------101/255---[IISSMP limits for 101 < IXSTAT < 255]

    NOTE:The last two limit sets can both be referred to as "Door Closed limit sets". Note also that "Door Closed limit sets" do include limit definitions that are "nominal", when the limit sets are defined this way.

    Delta limits

  • Delta limits are defined for some mnemonics. The exact same rules regarding the Switch Mnemonic applies to them. The delta limits also specify a Yellow and Red delta value, and a "trigger count" value. BUT NOTE THIS: For a delta limit to flag, the mnemonic in question has to change from one format to the next, by an amount exceeding the yellow or red delta limit, [trigger count] number of times in succession (each time exceeding the delta limit). They do *not* trigger if a change of twice the yellow or red limit occurs from one format to the next and the mnemonic then stays put (unless [trigger count] is 1)! And as a special bonus, the [trigger count] value from the database is ignored - the default value of 2 is used instead, except for a few select spacecraft mnemonics where the default is changed on the strings after startup.

  • In other words, the overwhelming majority of instrument delta limits are quite useless. This explains why all the delta limit violations on record (per December 2005) seem to have been either "unexplained", resulted in a limit change or halting monitoring for the mnemonic, or due to bad telemetry!

    Database update/version info

  • We are currently using Database 25 as of January 9 2006. The FOT updates the database infrequently, so for all limit changes, they update a file called x_lim_db25_ch.prc to temporarily update the limits for the database.

  • When we turn in an OCD with limit changes and the FOT makes the change, they should give us a new version of x_lim_db25_ch.prc. We then use that to update our copy of the database.

  • The database is stored electronically in /u/ecs/soc/limits. The limits are stored individually per instrument as text files and are called [instrument].limits. The original Excel files are in excel_orig25 directory. The limits are printed out and put in the front of the limits binder. Thermal_limits.limits are the QT* mnemonics.

  • The delta limits are in /u/ecs/soc/limits and are called [instrument]_delta.limits.

  • Any changes to the limits should be made on both the electronic and paper copies.
  • Location: /u/ecs/soc/info/limit_database_explanation_info.html